Arsenical pesticides: A symposium sponsored by the Division of Pesticide Chemistry at the 168th meeting of the American Chemical Society, Atlantic City, N.J., Sept. 9, 1974 (ACS symposium series ; 7)

Arsenical Pesticides Ε. A . Woolson, Editor

A symposium sponsored by the D i v i s i o n of Pesticide Chemistry at the 168th M e e t i n g of the American Chemical Society, Atlantic City, N. J., Sept. 9, 1 9 7 4 .

ACS

SYMPOSIUM

SERIES

7

AMERICAN CHEMICAL SOCIETY WASHINGTON,

D. C.

1975

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

Library of Congress CIP Data Arsenical pesticides. ( A C S symposium series; 7) Includes bibliographical references and index. 1. Pesticides—Environmental aspects—Congresses. 2. Arsenic compounds—Environmental aspects—Congresses. I. Woolson, Ε. Α., 1 9 4 1 - ed. II. American Chemical Society. III. American Chemical Society. Division of Pesticide Chemistry. I V . Series: American Chemical Society. A C S symposium series; 7. [DNLM: 1. Arsenicals—Congresses. 2. Pesticides—Congresses. QV294 A 5 1 2 1974] QH545.P4A77 I S B N 0-8412-0243-5

Copyright ©

574.5'222 74-31378 A C S M C 8 7 1-176 (1975)

1975

American Chemical Society All Rights Reserved

PRINTED IN THE UNITED STATES OF AMERICA

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

A C S Symposium Series Robert F. Gould,

Series Editor

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

FOREWORD The

A C S S Y M P O S I U M SERIE

a m e d i u m for publishing symposia q u i c k l y i n book form.

The

f o r m a t of the S E R I E S parallels that of its predecessor, A D V A N C E S I N C H E M I S T R Y S E R I E S , except that i n order to save t i m e the papers are not typeset b u t are r e p r o d u c e d as they are subm i t t e d b y the authors i n c a m e r a - r e a d y

form.

As a further

means of s a v i n g t i m e , the papers are not e d i t e d or r e v i e w e d except b y the s y m p o s i u m c h a i r m a n , w h o becomes e d i t o r of the book.

Papers p u b l i s h e d i n the A C S S Y M P O S I U M

SERIES

are o r i g i n a l c o n t r i b u t i o n s not p u b l i s h e d elsewhere i n w h o l e or major p a r t a n d i n c l u d e reports of research as w e l l as r e v i e w s since s y m p o s i a m a y e m b r a c e b o t h types of presentation.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

PREFACE A r s e n i c is a n e n v i r o n m e n t a l l y u b i q u i t o u s G r o u p V a element. A l t h o u g h it has a m e t a l l i c a l l o t r o p i c f o r m l i k e the t w o h i g h e r G r o u p V a elements,

a n t i m o n y a n d b i s m u t h , arsenic's

s i m i l a r to p h o s p h o r u s .

c h e m i c a l b e h a v i o r is q u i t e

It has f o u r valence states, —3, 0, + 3 ,

and

+5.

A r s i n e a n d methylarsines are characteristic of A s i n the —3 valence state a n d are generally unstable i n air. A r s e n i c m e t a l is f o r m e d b y r e d u c t i o n of arsenic oxides a n d is a glossy b l a c k m a t e r i a l .

A r s e n i c t r i o x i d e is a

p r o d u c t of s m e l t i n g operations, a n d it is the starting m a t e r i a l for synt h e s i z i n g most arsenica b a c t e r i a to arsenic p e n t o x i d e or orthoarsenic a c i d ( H A s 0 ) . 3

4

Arsines

a n d arsenites are generally m o r e toxic t h a n arsenates. I n the n a t u r a l e n v i r o n m e n t , most arsenicals d e g r a d e or w e a t h e r to f o r m arsenate, a l t h o u g h u n d e r anaerobic c o n d i t i o n s arsenite m a y f o r m . B i o t r a n s f o r m a t i o n s m a y o c c u r w h i c h result i n v o l a t i l e arsenicals.

These,

i n t u r n , are r e t u r n e d to the l a n d w h e r e soil a d s o r p t i o n , p l a n t u p t a k e , erosion, l e a c h i n g , r e d u c t i o n to arsines, or other processes occur.

This

n a t u r a l arsenic c y c l e reflects a constant s h i f t i n g of arsenic into the various environmental compartments. T h i s s y m p o s i u m was a r r a n g e d because of current c o n c e r n a n d interest i n the q u a l i t y of o u r e n v i r o n m e n t , p a r t i c u l a r l y as it pertains to trace h e a v y metals. W h i l e arsenic is not a h e a v y m e t a l , it is a m e t a l l o i d w h i c h has a l w a y s generated m u c h interest a n d controversy because m a n y of its c o m p o u n d s have toxic properties.

T h i s s y m p o s i u m , then, was i n t e n d e d

to examine the analysis, soil b e h a v i o r , biotransformations, a c c u m u l a t i o n s , c y c l i n g , a n d m o d e l i n g of arsenate a n d arsenical pesticides i n nature. E.

Beltsville,

A.

WOOLSON

Md.

N o v e m b e r 1,

1974

vii

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1 Review of Arsenical Pesticides S. A. PEOPLES School of Veterinary Medicine, University of California, Davis, Calif. 95616

It is not the purpos tive usefulness of various arsenic compounds as herbicides and insecticides. It is rather to present information which is needed to form the basis for evaluating the effects of such usage on the ecosphere and the p o s s i b i l i t y of adverse effects on animals and man. Arsenic has had such a bad name as to be nearly synonymous with the word "poison" and I think it would be worth putting it in i t s proper place. It is a relatively common element, present in a i r , water, s o i l , plants and animals, and the pharmacology of chemical compounds depends on the dose given; no action, useful and toxic. Considering that arsenic compounds have been known since 250C B.C. and used in medicine since the time of Hippocrates since 400 B.C. (1), one would expect that information would be available as to the chemical nature of arsenic compounds in nature and their biochemical effects and metabolic fate in plants and animals. Such is not the case, however, due in large part to the failure to develop analytical procedures for specific compounds. A l l samples were wet or dry ashed to inorganic arsenic, reduced to arsine with zinc and hydrochloric acid which was then quantitated by some modification of the Gutzeit method. The results were usually expressed as arsenic trioxide, a practice which has lead many to the conclusion that the arsenic in the sample was indeed trivalent arsenic and worse yet, toxicologists frequently use the term "toxicity of arsenic for animals" as synonymous with the toxicity of arsenic trioxide for animals (2). Recently, an analytical method has been developed in my laboratory which w i l l separately quantitate the inorganic and methylated arsenic in water, grass and urine (3) and is now being modified for s o i l samples. A method using a helium plasma has been introduced by Braman which w i l l separate trivalent and pentavalent inorganic arsenic and methyl and dimethyl arsonic acids (4). The use of these methods in combination with such isolation technics such as thin layer and column chromatography w i l l hopefully yield as much information about the biochemistry 1

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2 of

ARSENICAL

a r s e n i c as i s now

PESTICIDES

known about phosphorus.

Chemistry A r s e n i c occurs i n nature as s u l f i d e s such as orpiment and as complex s u l f i d e s or i r o n , n i c k e l and c o b a l t . I t has valences of 3 , 5 and i n o r g a n i c and o r g a n i c compounds o f both are known. A valence o f -3 i s a l s o known where a r s e n i c i s combined with hydrogen i n compounds known as the a r s i n e s . Since the s y n t h e s i s o f s a l v a r s a n by E h r l i c h i n 1905, l i t e r a l l y hundreds o f organic a r s e n i c a l s have been synthesized f o r use i n medicine and i n d u s t r y . Except f o r the treatment o f such p a r a s i t i c diseases such as trypanosomiasis, amebiasis and f i l a r i a s i s , the advent o f the a n t i b i o t i c s rendered most o f the m e d i c i n a l products obsolete but i t i s i n t e r e s t i n have found new uses unde tive. The information i n Table 1, taken from pharmacology textbooks used i n the 1930 s shows some o f these compounds and the therapeut i c dose l e v e l s should be o f p a r t i c u l a r i n t e r e s t to those concerned with t h e i r r e s i d u e l e v e l s i n food (5) (6). For example, i t would be necessary t o eat 10 kg o f food c o n t a i n i n g 5 ppm of c a c o d y l i c a c i d t o o b t a i n a t h e r a p e u t i c dose. +

+

f

D i s t r i b u t i o n of A r s e n i c i n Nature A r s e n i c i s a ubiquitous element present i n a i r , water, s o i l and a l l l i v i n g t i s s u e s . The f i n d i n g o f a r s e n i c i n any sample i s t h e r e f o r e not s i g n i f i c a n t unless compared t o the c o n c e n t r a t i o n normally expected. The range o f these values i s given i n Table 2 (7). I t must be p o i n t e d out that these values are given as t o t a l a r s e n i c and t h e i r chemical nature i s unknown. That high values occur i n sea food has been known s i n c e 1935 when Coulson reported i t i n shrimp and found i t to be nontoxic t o r a t s (18). I t i s c l e a r that animals and man r e c e i v e a d a i l y i n t a k e o f a r s e n i c which v a r i e s with geographical l o c a t i o n and type o f d i e t . Once again i t should be noted that the chemical nature o f the a r s e n i c i n these sources i s l a r g e l y unknown and t h e r e f o r e the f a t e and e f f e c t i n animals and man cannot be p r e d i c t e d . For example Lakso (3) found that most o f the background a r s e n i c i n Johnson grass was a methylated a r s o n i c a c i d , probably MSMA, a compound o f low t o x i c i t y . Absorption, D i s t r i b u t i o n and E x c r e t i o n A r s e n i c compounds can be absorbed by any route although the usual entry i s by i n g e s t i o n . There i s a common b e l i e f that a r s e n i c i s a cumulative poison which i s l a r g e l y based on i t s tendency t o accumulate i n high concentrations i n the h a i r and n a i I s , which are a c t u a l l y e x c r e t o r y products and not i n e q u i l i b rium with the l i v i n g body. A second b a s i s f o r t h i s b e l i e f i s the

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

PEOPLES

Review

TABLE 1 Arsenical Drugs Used in Treating Human Disease Drug Fowler's Solution

Dose grams

Use

Formula

.005 CH

Pearson's Solution

,005

Arrhenal

.05

3

NaOAs = 0 CH CH Na OAs = 0 CH / H Na OAs^O CH As = As

Tonic

X

3

3

Tonic

X

Sodium Cacodylate Arsphenamine

3

3

.05

Tonic

3

.3-6

Syphilis

ONH

ONHO

2

OH 0 Atoxyl

. 0 2 - 2 0 Trypanosomiasis

OH

Na OAs

(~}NH

2

OH 0 Tryparsamide

2.0

Trypanosomiasis

Carbarsone

.75

Amebiasis

Melarsoprol

.18

Trypanosomiasis

0

Na OAs ( )NH-CH -C-NH OH 0 0 II = , li NaOAs { >NH-C — N H OH 2

2

/

2

NH >~ 2

N

\ s — CH — C H 0 H

Pharmacotherapeutics A Manual o f Pharmacology

2

(5) (6)

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4

ARSENICAL

PESTICIDES

T a b l e II Concentration

Substance

o f A r s e n i c i n Nature

Concentration ppm

Water Soil

1.0

- 500.0

Grass

.1

1.6

Ferns

.2

3.64

Vegetables

.00 -

2.9

Grains

.11

Corn o i l

.00

Fish

o i l (ocean)

.16

-

1.0

5.0

Fish

2.0

9.0

Shellfish

1.6

-

2.9

Shrimp,

1.5

-

100.0

lobster

Meat

.06

1.07

Milk

.01

.05

J . Chronic Diseases (7)

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

PEOPLES

Review

5

use o f the r a t as an experimental animal i n a r s e n i c s t u d i e s , an animal which i s unique i n i t s a b i l i t y to s t o r e a r s e n i c i n i t s red blood c e l l s . Table 3 (9) shows the normal values i n the t i s s u e s o f common experimental animals and t h e i r response to the feeding o f a r s e n i c . I f man were i n c l u d e d i n the t a b l e he would have values s i m i l a r to those o f the r a b b i t with values o f a l l t i s s u e s v a r y i n g between .05 and .30 ppm. Milk i s e x c e p t i o n a l l y low i n a l l animals, being .01 - .03 ppm. H a i r and n a i l s normally have 1.0 - 5.0 ppm but due to the f a c t that they r e a d i l y p i c k up a r s e n i c from the environment, such values are o f u n c e r t a i n value i n r e f l e c t i n g p o i s o n i n g . Blood values are u s e f u l i n measuring the body burden and r a t e o f change i n the body as shown i F i g 1 (10) Th clearanc rate clearl i l l u s t r a t e the d i f f e r e n c e l y slow r a t e i n the r a t The route o f e x c r e t i o n i s i n the u r i n e and feces and the shape o f the e x c r e t i o n curve i n the r a t e as shown i n F i g . 2 (11), showing that there i s a f a s t phase followed by a slow one, i n d i c a t i n g that there are two storage p o o l s . The a r s e n i c l e v e l i n the milk o f cows does not increase with the blood concentration when fed i n o r g a n i c a r s e n i c , methyl a r s o n i c a c i d or c a c o d y l i c a c i d as i l l u s t r a t e d i n F i g . 3 (12). This may mean that there i s an a c t i v e t r a n s f e r o f a r s e n i c i n the mammary gland which i s saturated at a l l times. From a residue p o i n t o f view, the presence o f even t o x i c amounts o f a r s e n i c i n animal feed w i l l not e f f e c t the s a f e t y o f milk. The u r i n a r y e x c r e t i o n o f a r s e n i c i n u r i n e has been suggested as a measure o f exposure but i t i s of no value unless the d i e t i s known. Schrenk (13) found that the e a t i n g o f sea food, p a r t i c u l a r l y Crustacea, r a i s e d the u r i n a r y a r s e n i c l e v e l s by as much as 10-fold, r e t u r n i n g to normal i n 20 - 40 hours as shown i n F i g . 4. T h i s i s due t o the compound known as Coulsons "Shrimp A s e n i c " and i l l u s t r a t e s i t s r a p i d abs o r p t i o n and e x c r e t i o n . Metabolism of A r s e n i c The preceeding studies on the d i s t r i b u t i o n and e x c r e t i o n o f a r s e n i c are based on t o t a l a r s e n i c determinations and say nothing of the chemical changes that might occur. Gosio (14) noted i n 1893 that c e r t a i n molds growing on wallpaper c o n t a i n i n g a r s e n i c a l pigments produced a t o x i c gas which was i d e n t i f i e d by Challenger (15) i n 1931 as t r i m e t h y l a r s i n e and could a l s o be produced from sodium a r s e n i t e and c a c o d y l i c a c i d . Recently McBride (16) r e ported that a methanobacterium could methylate i n o r g a n i c asenic to form dimethyl a r s o n i c a c i d and dimethyl a r s i n e under anaeorbic c o n d i t i o n s . T h i s f i n d i n g suggested t o us that the methyl a r s o n i c a c i d we had found i n bovine u r i n e (17) need not e n t i r e l y come from grass which contains methylated a r s e n i c (3) but could have been produced by the anaerobic b a c t e r i a i n the rumen. Preliminary

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.0

0.0

Fed

Control

15.0

0.0

Control

Fed

1.0

0.0

20.0

0.0

Fed

Control

Fed

Control

Liver

* F o u r in each group.

Hamster

Rabbit

Pig

Guinea

Rat

Animal*

7.0

0.0

0.2

0.0

20.0

0.0

43.0

3.3

Heart

5.0

0.0

1.5

0.0

1.0

0.0

25.0

1.5

2.0

0.0

0.2

0.0

15.0

0.0

60.0

0.67

Kidney Spleen

0.7

0.0

0.2

0.0

0.8

0.0

12.0

0.6

Fat

2.5

1.8

0.2

0.0

2.0

0.0

3.0

0.7

Muscle

30.0

1.5

1.5

0.1

2.0

1.0

15.0

0.6

38.0

0.0

2.5

0.0

—

0.0

27.0

0.6

Skin

2.5

0.0

1.5

0.1

4.0

0.0

125.0

15.0

Blood

Ann. N. Y. Acad. Science (9)

1.0

0.0

0.0

0.0

0.0

0.0

3.8

0.5

Brain

Tissue concentration of arsenic ppm G.I. tract

D A Y S OF F E E D I N G A D I E T

CONTAINING 50 PPM ARSENIC TRIOXIDE

T H E ARSENIC CONCENTRATION IN TISSUES A F T E R 21

TABLE 3

1.

PEOPLES

Review

7

Concentration of arsenic per gram of blood at a particular time is expressed as per cent of the administered dose per gram of body weight (10). 76

University of California Publications in Pharmacology

TIME

IN

HOURS

Figure 2. Total fecal and urinary elimination of carrier-free As by rats (11) 74

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL

8

5

10

15

PESTICIDES

20

DAY OF FEEDING TRIAL - HOLSTEIN COW Figure 3.

2.o r

T i m e , H o u r s , After Eating American Industrial Hygiene Association Journal

Figure

4.

Concentration

of arsenic in urine following

the eating of

lobster

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

PEOPLES

9

Review

experiments have shown that the feeding of e i t h e r sodium a r s i n a t e or sodium a r s i n i t e r e s u l t s i n a great increase i n methyl a r s o n i c acids i n the u r i n e , a f i n d i n g which seemed t o confirm t h i s hypothe s i s . To show that the rumen was necessary f o r t h i s methylation the same experiments have been repeated i n dogs, and i f confirmed by f u r t h e r experiments, the c a r n i v o r e can methylate i n o r g a n i c a r s e n i c as w e l l as the ruminant. Experiments are now under way to f i n d the r o l e , i f any, o f the rumen, and the biochemical mechanism of the methylation o f a r s e n i c i n the dog. The o r i g i n o f methyl a r s o n i c a c i d i n normal p l a n t s i s s t i l l to be explored, but one could p o s t u l a t e that i t could be o f animal o r i g i n . The work o f Braman (4) i n d i c a t e d that methylated a r s e n i c compounds are probably q u i t e common i n man and nature and only a small beginning has bee I t should be pointe causes a great r e d u c t i o n i n t o x i c i t y and i s a true d e t o x i c a t i o n process. Toxic E f f e c t s o f A r s e n i c The t o x i c i t y o f t r i v a l e n t i n o r g a n i c a r s e n i c f o r l i v i n g organisms v a r i e s widely as shown i n Table 4. Table 4 Item Bacteria Algae Yeast Daphnia

Arsenite 290

magna

Flatworms Minnows Minnows Minnows Rats and mice, 96 hr LD50 o r a l MLD, i n t r a p e r i t o n e a l

Arsenate > 10,000 > 1,000 300

5.2

12.5

40 20 17.8 11.6 11.2 5.8 J . Chronic

361 250 234 60 112 21 Diseases

(7)

The t o x i c dose f o r r a t s o f a r s e n i c a l h e r b i c i d e s i s shown i n Table 5, which are average values from a v a r i e t y o f sources. The mechanism o f t o x i c i t y i s considered to be due to the binding o f - SH groups o f l i p o i c a c i d by t r i v a l e n t a r s e n i c . However, pentavalent a r s e n i c compounds behave l i k e phosphate i n biochemical r e a c t i o n s yet symptoms o f poisoning are s i m i l a r f o r a l l a r s e n i c compounds. I t may be found that they can be reduced t o t r i v a l e n t a r s e n i c by mechanisms p r e s e n t l y unknown. The f a c t

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

10

ARSENICAL

PESTICIDES

Table 5 T o x i c i t y o f A r s e n i c a l H e r b i c i d e s f o r Rats Compounds Sodium A r s e n i t e Sodium Arsenate Sodium Methyl Arsenate (MSMA) Sodium Cacodylate

T o x i c Dose mg/kg 20 80 1200

60 120 1600

1200

1600

that BAL, 2,3 dimercaptopropanol, i s used with some success i n a l l forms o f a r s e n i c p o i s o n i n Acute t o x i c i t y i s the usua ment o f acute e n t e r i t i , there i s extensive l i v e r and kidney damage as w e l l . The p o s s i b i l i t y o f c h r o n i c a r s e n i c p o i s o n i n g from continuous i n g e s t i o n o f small doses i s r a r e , due t o the d e t o x i c a t i o n and e x c r e t i o n being f a i r l y rapid. A r s i n e i s a gas formed i n the presence o f a c i d and hydrogen and i s t o x i c i n very low cencentrations i n i n h a l e d a i r . I t causes hemolysis o f the r e d c e l l s , r e s u l t i n g i n anemia, hemog l o b i n u r i a with r e s u l t i n g r e n a l damage. I t i s r a p i d l y f a t a l and there i s no known a n t i d o t e . As p r e v i o u s l y noted, McBride (16) has shown that dimethyl a r s i n e can be produced i n the b a c t e r i a found i n the mud o f waterways and suggested i t could cause t o x i c i t y . T h i s p o s s i b i l i t y seems remote since dimethyl a r s i n e bums spontaneously i n a i r . The q u e s t i o n o f a r s e n i c as a cause o f cancer has been s t u d i e d f o r a century without a c l e a r d e c i s i o n . When a r s e n i c t r i o x i d e i s a p p l i e d t o the s k i n o r taken o r a l l y i n l a r g e doses h y p e r k e r a t o t i c l e s i o n s appear on the s k i n with a delay o f many years i n some cases. These l e s i o n s are precancerous but they can a l s o be caused by s u n l i g h t , x-ray and thermal burns. Cancer has not been produced i n experimental animals by any a r s e n i c compound. The incidence o f cancer i n a r s e n i c i n d u s t r i e s i s e q u i v o c a l i s s p i t e of c o n t i n u i n g s t u d i e s (18). Conclusion The use o f new a n a l y t i c a l methods w i l l h o p e f u l l y e l u c i d a t e the r o l e o f a r s e n i c i n the ecosphere and may even demonstrate that i t i s e s s e n t i a l i n l i v i n g t i s s u e . The high l e v e l s i n sea animals which are constant i n value and not r e l a t e d t o i n d u s t r i a l o r a g r i c u l t u r a l p o l l u t i o n , suggest t h i s p o s s i b i l i t y . While much research needs t o be done, enough i s known about the u s e f u l and t o x i c e f f e c t s o f a r s e n i c compounds so that t h e i r use as p e s t i c i d e s and feed a d d i t i v e s can be c a r r i e d out with s a f e t y .

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.

PEOPLES

Review

Literature Cited 1.

Vallee, B . L . , Ulmer, D.D., and Wacker, W.E.C. "Arch. of Industrial Health." Arsenic Toxicology and Biochemistry 21:132-151, (1960).

2.

Luh, M.D., Baker, R.A., and Henley, D.E. "Arsenic Analysis and Toxicity - A Review." Science of the Total Environ. 2:1-12, (1973).

3.

Lakso, J . U . , Peoples, S.A., and Bayer, D.E. "The Simultaneous Determinations of MSMA and Arsenic Acid i n Plants." Weed Science 21:166-169, (1973).

4.

Braham, R.S., and Arsenic in the Environment."

5.

S. Soles-Cohen and T.S. Githens, Pharmacotherapeutics, D. Appleton, New York, (1928).

6.

T. Sollman, A manual of Pharmacology, 7th E d . , W.B. Saunders, Philadelphia, (1948).

7.

Schroeder, H . A . , and Balassa, J.B. "Abnormal Trace Elements in Man:Arsenic." J . Chronic Diseases 19:85-106, (1966).

8.

Coulson, E . V . , Remington, R . E . , and Lynch, K.M. "Metabolism i n the Rat of the Naturally Occurring Arsenic of Shrimp as Compared with Arsenic Trioxide." J . Nutr. 10:255-270, (1935).

9.

Peoples, S.A. "Arsenic Toxicity i n C a t t l e . " Acad. Science 111:644-649, (1964).

10.

Ducoff, H.S., Neal, W.B., Straub, R . L . , Jackson, L . O . , and Brues, A.M. "Biological Studies with Arsenic II Excretion and Tissue Localization." Proc. Soc. Exper. Biol. Med. 69:548-554, (1948).

11.

Lanz, H . , Jr., Wallace, P.W., and Hamilton G. "The Metabolism of Arsenic in Laboratory Animals Using 74 As as a Tracer. Univ. of C a l i f . Pub. in Pharmacol. 2:263-282, (1950).

12.

Peoples, S.A., Unpublished.

Science 182:1247-1249, (1973).

Ann. N. Y.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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ARSENICAL PESTICIDES

13.

Schrenk, H.H., and Schreibeis, L., Jr. "Urinary Arsenic Levels as an Index of Industrial Exposure." Am. Ind. Hyg. Assoc. J. 19:225-228, (1958).

14.

Gosio, B.

15.

Challenger, F. Biological Methylation. 315-361, (1945).

16.

McBride, R.C., and Wolfe, R.S. "Biosynthesis of Dimethyl Arsine by Methanobacterium." Biochem. 10:4313-4317, (1971).

17.

Peoples, S.A., Lakso, J., and Lais, T. "The Simultaneous Determination of Methylarsonic Acid and Inorganic Arsenic in the Urine." Proc (1971).

18.

E. Browning, Toxicity of Industrial Metals, AppletonCentury-Crofts, New York, (1969).

Arch Ital. Biol.

18:253-298, (1893). Chem. Rev. 36:

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2

T h e Determination of Traces of Arsenic: A Review* YAIR TALMI and CYRUS FELDMAN Oak Ridge National Laboratory, Oak Ridge, Tenn. 37830**

This review is organize characterizing a l l trac analysis sampl pretreatmen solution, solution stability, preconcentration, isolation and determination. The options now existing in each step have been presented, but no attempt is made to mention every investigation in which each has been used. It is hoped that this treatment will make i t easier for the analyst to assemble a procedure suited to the needs of a particular case. Pretreatment and Dissolution of the Sample If total arsenic is to be determined, the sample must be mineralized at least to the degree necessary to convert a l l arsenic present to inorganic forms. The treatment chosen should be the mildest treatment which will accomplish this conversion, so that losses and contamination will be minimized. Several approaches are possible:*** 1.Wet Ashing. According to Portmann and Riley1, prolonged digestion with nitric acid, followed by evaporation to dryness (hot-plate surface temperature ~180 ) will give no losses of arsenic, even i f several mg of chloride were originally present. This type of attack could be used for materials such as vegetation * Research supported by the National Science Foundation—RANN (Environmental Aspects of Trace Contaminants) Program under NSF interagency agreement No.389 with the U.S. Atomic Energy Commission. **Operated for the U.S. Atomic Energy Commission by Union Carbide Corporation under Contract No. W-7405-Cong.-26. *** A general and more detailed treatment of this subject is given in T.T. Gorsuch's book "The Destruction of Organic Matter", Pergamon, NYC (1970). º

13 In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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ARSENICAL PESTICIDES

and animal muscle. Stronger treatment i s u s u a l l y advocated f o r other organic m a t e r i a l s , e s p e c i a l l y those high i n l i p i d s ; however, Kingsley and S c h a f f e r t ^ s t a t e that a l l of the a r s e n i c present i n l i v e r , kidney o r muscle can be recovered merely by d i g e s t i n g the b l e n d e r i z e d t i s s u e f o r 30 minutes i n ^4N HC1. The d i g e s t i o n must be open to the atmosphere, so that s u l f i d e s and mercaptans (which may i n t e r f e r e w i t h subsequent determination of As) w i l l be e l i m i nated. S i m i l a r l y , R.F. Abernethy and F.H. Gibson** s t a t e that e s s e n t i a l l y 100% o f the a r s e n i c a l species i n c o a l can be e x t r a c t e d by b o i l i n g the powdered c o a l gently i n a 1:7 mixture of HNO3 and H 0. The HNO3 may then be e l i m i n a t e d , i f d e s i r e d , by adding 1:1 H2SO4 and evaporating the s o l u t i o n to fumes. According to R.B. B a i r d , S. Pourian and S.M. G a b r i e l i a n , raw sewage and primary and secondary e f f l u e n t s can be m i n e r a l i z e d by r e f l u x i n g with 4% HNO3 + 1% H2O2, followed by evaporatio Cacodylates sprayed on shaking w i t h a mixture o f strong H2SO4 and HC1 p l u s d e c o l o r i z i n g carbon. Hamme, Young and Hunter-* s t a t e that recovery by t h i s r a p i d method averages 93%. Other treatments have a l s o been advocated which do not necess a r i l y m i n e r a l i z e b i o l o g i c a l samples completely, but l i b e r a t e their metals to a degree s u f f i c i e n t f o r some types of a n a l y s i s . W. J . A d r i a n , f o l l o w i n g G.W. Gordon, l e f t the sample overnight, w i t h HNO3 and HCIO4, i n a t i g h t l y sealed polyethylene b o t t l e . The b o t t l e was then placed i n hot running water f o r 2-3 hours, cooled and opened. Rapid d i s s o l u t i o n of t i s s u e s was a l s o achieved by A. Bouc h a r d using coned. H2SO4, Cr03 and red fuming HNO3 ( p o s s i b l e contamination from reagents must be considered i n t h i s case). Many t i s s u e s can a l s o be transformed i n t o c l e a r s o l u t i o n s with the a i d of tetramethylammonium hydroxide, e i t h e r i n s o l i d o r aqueous s o l u t i o n form** or as a s o l u t i o n i n toluene^. Heating a t 60°C may be r e q u i r e d . Many o f these milder procedures do not a t t a c k f a t t y and h i g h - l i p i d t i s s u e s or bone and tooth specimens. When stronger treatment i s needed, some combination of n i t r i c , s u l f u r i c and p e r c h l o r i c acids i s u s u a l l y used. In a t y p i c a l p r o cedure of t h i s type, Chu, Barron, and Baumgarner^ a l t e r n a t e l y heat the sample i n a mixture of s u l f u r i c and n i t r i c acids u n t i l the s o l u t i o n darkens, then add more HNO3, and repeat the process u n t i l darkening no longer occurs; they complete the o x i d a t i o n by heating with HCIO4. S a n d e l l recommends the use of r e f l u x i n g with such procedures i n order to prevent the l o s s of AS2O3 and/or ASCI3. I f the a r s e n i c i s e v e n t u a l l y to be reduced to A s 3 f o r determination, the excess HNO3 remaining a f t e r wet-ashing can be destroyed by t r e a t i n g the mixture with a few ml o f saturated ammonium oxalate and warming. G.I. S p i e l h o l t z , G.C. T o r a l b a l l a , and R.J. S t e i n b e r g - ^ r a p i d l y (and s a f e l y ) m i n e r a l i z e d powdered c o a l by r e f l u x i n g i t w i t h a mixture of 68-70% HCIO4 and para-HI04. P. Schramel-^*-^ showed that reagent blanks i n the d i s s o l u t i o n of 150 mg t i s s u e samples can be minimized by warming the samp l e with 100 y l coned. H S0^ and adding 50% H 02 s o l u t i o n dropwise. 2

6

7

1 1

+

2

2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2. TALMI AND FELDMAN

15

Traces of Arsenic

1

T h i s i s a refinement of W. Migault's "Caro's a c i d " procedure -*. * Dry Ashing. Various procedures i n v o l v i n g MgO/Mg(1*03)2 a d d i t i o n have been recommended f o r dry-ashing vegetable and animal t i s s u e s . One r e c e n t , widely a p p l i c a b l e procedure suggested by George, Frahn and McDonald ** i n v o l v e s p r e l i m i n a r y b l e n d e r i z i n g o f the t i s s u e , treatment with MgO and c e l l u l o s e powder and an i n i t i a l cautious c h a r r i n g i n a p o r c e l a i n c r u c i b l e . When c o o l , the crucible i s t r e a t e d w i t h Mg(N03)2 • 6H2O and placed i n a c o l d muffle f u r nace. The temperature o f the furnace i s slowly r a i s e d t o 555°, and kept there f o r 2 hours. Good recovery was obtained f o r 1-2 ppm spikes added to samples. R.F. Abernethy and F.H. Gibson** obtained q u a n t i t a t i v e recovery o f As from c o a l by i g n i t i n g i t w i t h MgO a t 650°C; the residue was d i s s o l v e d i n 7N R^SO,. 3. Oxygen Combustion The Schoniger combustion method * (Ignition o f a sample i bing s o l u t i o n ) was use They obtained q u a n t i t a t i v e recovery o f As on 0.5 g d r i e d specimens with a 750 ml f l a s k c o n t a i n i n g 0 and 5 ml o f 3N HC1. I g n i t i o n i n a metal bomb c o n t a i n i n g Oo was a l s o found s a t i s f a c t o r y by H.S. S a t e r l e e and G. B l o d g e t t * . According to C.E. G l e i t and W.D. H o l l a n d , b i o l o g i c a l t i s s u e s , as w e l l as other substances can be m i n e r a l i z e d a t a low temperature by using e l e c t r i c a l l y e x c i t e d oxygen. Complete recovery o f As i s obtained from blood t r e a t e d with HAs0 . 4. Fusion. Minerals are u s u a l l y fused with NaOH i n a s i l v e r or n i c k e l c r u c i b l e ; e.g., by H. O n i s h i and E.B. S a n d e l l . These authors s t a t e that l o s s e s of As are 0.5%; e s s e n t i a l l y a l l of the As i s recovered i n the l e a c h liquid*«even when a r e s i d u e i s p r e sent. J.A. James and D.H. Richards have a l s o a p p l i e d t h i s f u s i o n to the determination of As i n elemental S i . 2

1

1

7

l

g

2

2

2 1

2

2 2

S t a b i l i t y o f Sample S o l u t i o n s During

Storage

T h i s d i s c u s s i o n p e r t a i n s mainly to n a t u r a l water samples and standards, s i n c e the sample s o l u t i o n s produced by any o f the above methods are normally analyzed soon a f t e r p r e p a r a t i o n . To t e s t the s t a b i l i t y of As a t low concentrations i n sea water, J.E. Portmann and J.P. R i l e y f i l t e r e d each sample through a 0.5u M i l l i p o r e f i l t e r , and t r e a t e d the f i l t r a t e with 5 C i o f c a r r i e r - f r e e ^As. Samples i n soda-glass b o t t l e s l e v e l l e d o f f a t 16% l o s s a f t e r 16 days; samples i n polyethylene and b o r o s i l i c a t e g l a s s l e v e l l e d o f f a t 6% l o s s a f t e r 10 days. These authors advise storage o f such samples i n frozen form i n polyethylene c o n t a i n e r s . G.C. Whitnack and R.G. Brophy ^ made small a d d i t i o n s of Na3As03 s o l u t i o n t o well-water samples, and s t o r e d them i n 25 ml p o l y s t y rene v i a l s with polyethylene caps. No l o s s of A s ( I I I ) from these s o l u t i o n s was d e t e c t a b l e a f t e r one week. A.S. A l - S i b b a i and A.G. F o g g ^ measured the s t a b i l i t y o f s o l u t i o n s o f both As (III) and As (V) i n v a r i o u s containers a t the 4-20 ug/ml l e v e l . Samples of AS2O3 were d i s s o l v e d i n NaOH s o l u t i o n and the s o l u t i o n n e u t r a l i z e d . T h i s s o l u t i o n kept i t s f u l l t i t e r f o r 56 days i n b o r o s i l i c a t e glass, soda g l a s s and polyethylene c o n t a i n e r s , i n both l i g h t and dark 1

7

2

2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL PESTICIDES

16

storage areas. S o l u t i o n s of NaHAsC>4 • 7H2O i n water d i d the same for 100 days under the same c o n d i t i o n s . R.S. Braman notes that very low concentrations of As species tend to disappear r a p i d l y from n a t u r a l water samples. In our l a b o r a t o r y , however, no l o s s e s of ^As(V) were experienced i n d i s t i l l e d water (polyethylene and s o f t g l a s s containers) 15% HNO3 or 5% HCIO4 s o l u t i o n (soft g l a s s containers) over a p e r i o d of 3 weeks. 26

2 7

7

Preconcentration and I s o l a t i o n of As Species The methods described i n t h i s s e c t i o n are o r i e n t e d toward the eventual determination of t o t a l (inorganic) As, r e g a r d l e s s of the o r i g i n a l molecular form i n which the As occurs. The p r i n c i p a l methods which have been used to preconcentrate As species are cop r e c i p i t a t i o n and adsorption, v o l a t i l i z a t i o n and l i q u i d - l i q u i d extraction. 1. C o p r e c i p i t a t i o Adsorption Fe(0H) for some time to be an e f f i c i e n t c o l l e c t o r of arsenate i o n . For example, R. P i e r u c c i n i c o l l e c t e d 100 yg of As(V) from 24 l i t e r s of water (= 4 ng/ml) by using 150 mg o f Fe(0H)3 (the As was then determined s p e c t r o g r a p h i c a l l y ) . J.E. Portmann and J.P. R i l e y , p r e c i p i t a t i n g Fe(0H)~ at pH 7, recovered 99% o f the 2 ug of As(V) present i n a l i t e r or water (2 ng/ml). T h i s procedure has a l s o been used to c o l l e c t As f o r determination by the G u t z e i t ^ and xanthate-^0 e x t r a c t i o n procedures. V . I . P l o t n i k o v and L.P.Usatova31 c a r r i e d out numerous c o p r e c i p i t a t i o n experiments i n 50 ml of s o l u t i o n . They found that at pH 7, As(V) i s q u a n t i t a t i v e l y c a r r i e d down by the hydroxides of Ce, Z r , In, Fe, T i and A l . The y i e l d decreases, e s p e c i a l l y f o r A l a t pH >8. In a l l cases, c o p r e c i p i t a t i o n was more e f f i c i e n t than the a d d i t i o n to the As(V) s o l u t i o n of a prepared hydroxide s l u r r y . For A s ( I I I ) , e f f i c i e n t (-95%) coprec i p i t a t i o n was obtained only with In and Zr hydroxides at pH 8.5. W. R e i c h e l and B. G. B l e a k l e y obtained complete recovery of 0.23.0 mg of As(V) (as w e l l as s i m i l a r amounts of Se, Te, Sb, Sn, B i , Pb and Fe) from 20g o f Cu by c o p r e c i p i t a t i n g with La(OH)3 a t pH 910. P.M. S a n t o l i q u i d o removed c a r r i e r - f r e e ^As(V) q u a n t i t a t i v e l y from a 7N HNO3 s o l u t i o n by passing i t through a 7 x 40 mm c o l umn of hydrated Mn02» The c a p a c i t y of t h i s column f o r As(V) i s greater than 272 yg As(V)/g MnOo. Z.G. H a n n a used Mg(0H) as a c o p r e c i p i t a n t : 0.3 yg As(V) i n 10 ml was treated with MgC^ + NB^Cl, and then with NH4OH. The p r e c i p i t a t e obtained was d r i e d , and i g n i t e d a t 600°C. No As was l o s t . 2 8

1

2

3 2

3 3

7c

34

2

T h i o n a l i d e i s s o l u b l e i n acetone, but i n s o l u b l e i n water. J.E. Portmann and J.P. R i l e y , making use of t h i s f a c t , added an acetone s o l u t i o n of t h i o n a l i d e to a 0.5N H2SO4 s o l u t i o n of 50 ng A s ( I I I ) + t r a c e r i n 1 l i t e r of sea water. The s o l u t i o n was s t i r r e d , b o i l e d 30 min. to remove acetone, and allowed to stand overnight. The p r e c i p i t a t e , c o n s i s t i n g almost e n t i r e l y of t h i o n a l i d e i t s e l f , was wet-ashed with concentrated HNO3. Recovery of As was 95%. Talmi, et a l . found that the high s a l t content of the sample sol u t i o n seems to be necessary to insure complete p r e c i p i t a t i o n ; 1

2 7

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TALMI AND FELDMAN

17

Traces of Arsenic

however, overnight storage i s unnecessary i f the p r e c i p i t a t i o n i s performed a t M)°C. Small amounts of A s ( I I I ) (reduced from As(V) i f necessary with KI) were c o l l e c t e d by a s u l f i d e procedure by V.V. Sergeeva, I.S. L e v i n , L . I . Tishchenko and V.S. Dankova ^. I n t e r f e r i n g elements were f i r s t removed by cupferron p r e c i p i t a t i o n and f i l t r a t i o n . Thioacetamide was added to the f i l t r a t e , and h y d r o l i z e d by heating the s o l u t i o n . The r e s u l t i n g AS2S3 p r e c i p i t a t e was c o l l e c t e d by c e n t r i f u g a t i o n ; the y i e l d was 85%. 3

3 6 , 3 7

2. L i q u i d - L i q u i d E x t r a c t i o n . A.K. K l e i n and F.A. V o r k e s were among the f i r s t to use xanthates to e x t r a c t A s ( I I I ) from food and biochemical t i s s u e s . In t h i s case, the f i r s t c o l l e c t i o n was done w i t h F e ^ H ) ^ ; the f i n a l determination, with arsenomolybdate. P.F. Wyatt 8,39 j diethylammoniu CHCI3 t o i s o l a t e As. Sinc s e v e r a l p o t e n t i a l l y i n t e r f e r i n g metals were removed i n i t i a l l y by f i r s t performing t h i s e x t r a c t i o n with As i n the pentavalent s t a t e . As was then reduced to A s ( I I I ) , and e x t r a c t e d from 1-10N ^ S O ^ s o lutions. Some p o t e n t i a l i n t e r f e r e n c e s not e l i m i n a t e d i n t h i s way [Cu, B i , S b ( I I I ) ] can be removed by a p r e l i m i n a r y e x t r a c t i o n w i t h cupferron. According to T.J. V e l e k e r ^ , t h i s reagent can be used to e x t r a c t A s ( I I I ) away from Ge, Sb and B i i n 6N HC1. H. M a l i s s a and E. Schoffmanual found that A s ( I I I ) could be p r e c i p i t a t e d by ammonium p y r r o l i d i n e dithiocarbamate (APDC), as w e l l as by other dithiocarbamates a t pH 2-6. C.E. M u l f o r d used a methyl i s o b u t y l ketone s o l u t i o n o f APDC to e x t r a c t A s ( I I I ) f o r determination by atomic absorption. V.V. Sergeeva, I.S. L e v i n , L . I . Tishchenko and V.S. D a n k o v a , using an 0.5N s o l u t i o n of d i - 2 - e t h y l h e x y l d i t h i o phosphoric a c i d i n decane and organic/aqueous volume r a t i o s of 1:1 to 1:30, e x t r a c t e d t r a c e s o f A s ( I I I ) from 0.5N a c i d aqueous s o l u t i o n s . The As was recovered from the organic phase by shaking with bromine water. A . I . Busev and M.I. I v a n i u t i n found that a s i m i l a r reagent, d i e t h y l d i t h i o p h o s p h o r i c a c i d , used s i m i l a r l y , e x t r a c ted A s ( I I I ) from e i t h e r weakly or s t r o n g l y a c i d i c aqueous solutions. Perhaps the simplest of the procedures f o r segregating As i s E. G a g l i a r d i and H.P. W o s s ' s ^ e x t r a c t i o n of A s C l from 6-7N HC1 i n t o a mixture of 2 volumes of CCI4 w i t h 3 volumes of 2-butanone, 2-pentanone or 2-heptanone. As with other e x t r a c t a n t s , p o t e n t i a l l y i n t e r f e r i n g elements can be e l i m i n a t e d by conducting a p r e l i m i n a r y e x t r a c t i o n w i t h the As i n the pentavalent s t a t e . According to A.R. B y r n e ^ , ASI3 can be e x t r a c t e d with toluene from a s o l u t i o n 12N i n H2SO4 and 0.05 M i n KI. I t can be s t r i p p e d from the toluene with 6N H S 0 + 0 . 0 5 M KI. 3

u s e (

4 2

35

4 3

3

2

4

3. V o l a t i l i z a t i o n . The p r i n c i p a l forms i n which As i s v o l a t i l i z e d f o r a n a l y t i c a l purposes are as a t r i h a l i d e and as a simple or s u b s t i t u t e d t r i h y d r i d e ( a r s i n e ) . A f t e r b i o l o g i c a l m a t e r i a l was decomposed with H S0^ + HNO3, E.B. S a n d e l l d i s t i l l e d AsBr^, using a special s t i l l . Some P and Sn were a l s o d i s t i l l e d . G.R. Kings ley and R.R. S c h a f f e r t noted that a r s e n i c compounds can be leached from t i s s u e homogenates w i t h 1+2 HC1, but that the operation must 1

2

2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

18

ARSENICAL PESTICIDES

be performed i n the open, r a t h e r than under t o t a l r e f l u x i f arseni c i s then to be d i s t i l l e d o f f as A s C l ^ . This p r e c a u t i o n i s taken i n order to expel R^S and mercaptans which would otherwise tend to prevent the d i s t i l l a t i o n of ASCI3. Recent years have seen a r a p i d growth i n the use of a r s i n e e v o l u t i o n as a method of separ a t i n g As from i t s o r i g i n a l matrix. Most authors who have used Zn° i n a c i d to generate AsH^ (e.g. R.E. Madsen , F . J . Fernandez and D.C. M a n n i n g ) have f i r s t reduced the As to A s ( I I I ) w i t h Sn&2 and/or KI. E.N. P o l l o c k and S.J. W e s t used T i C l 3 f o r the p r e l i m i n a r y r e d u c t i o n and Mg° i n a c i d f o r generating AsH^. F.E. Lichte and R.K. Skogerboe ^, however, i n j e c t a small volume of a c i d samp l e s o l u t i o n i n t o a columm of granular Zn°; the sample i s forced through the column by a stream of argon. The AsH^ thus generated passes w i t h the argon i n t o the d e t e c t i o n system R.S Braman L.L. Justen and C.C. F o r e b a c k to ASH3. They f i n d tha A s ( I I I ) by c o n t r o l l i n g the pH of the sample s o l u t i o n : As(V) i s r e duced only i f pH ^1.5. The NaBH^ can be i n j e c t e d as a s o l u t i o n , or by dropping a p e l l e t of the s o l i d reagent i n t o the sample s o l u t i o n by means of an e x t e r n a l l y operated hopper as suggested by F.J. Fernandez . R.N. S a n d e l l , as w e l l as R.S. Braman, L.L. Justen and C.C. Foreback ^ caution that e a s i l y reduced ions such as Cu(II) may i n t e r f e r e w i t h the production of ASH3. A f t e r generation, the ASH3 (b.p.-55°C) may e i t h e r be passed d i r e c t l y i n t o the d e t e c t i o n device or accumulated i n a l i q u i d n i t r o g e n - c o o l e d trap and released to the d e t e c t o r over a very short p e r i o d of time by warming the trap (see below). 47

4 8

4

51

1 1

5

Methods of Determination 1. Molecular Absorption—Spectrophotometry. There are a few reagents which produce i n t e n s e - c o l o r d e r i v a t i v e s w i t h a r s e n i c . However, two of them, s i l v e r - d i e t h y l d i t h i o c a r b a m a t e (Ag-DDC) and ammonium molybdate are u n i v e r s a l l y accepted as most s u i t a b l e f o r spectrophotometric measurements. The Ag-DDC reagent i s u s u a l l y used i n c o n j u n c t i o n with the a r s i n e generation m e t h o d * . A r s i n e i s passed through 0.5% Ag-DDC s o l u t i o n i n p y r i d i n e and the i n t e n s i t y of the red c o l o r i s measured at 533 nm. Beer's law i s obeyed over the 1-20 yg As range and the l i m i t of d e t e c t i o n i s below 0.1 ppm. The arseno-molybdate complex i s considered more s u i t a b l e by many because of i t s s e n s i t i v i t y , r e l i a b i l i t y and general freedom from i n t e r f e r e n c e s . Arseno-molybdic a c i d , formed by the reaction of arsenate with a c i d i f i e d molybdate, i s reduced to the blue comp l e x , the a b s o r p t i o n of which i s measured s p e c t r o p h o t o m e t r i c a l l y . SnCl2 i s used by a few workers f o r r e d u c t i o n ^ " , but produces an unstable c o l o r . Others use hydrazine sulfate 9»60 but r e d u c t i o n i s slow. Portmann and R i l e y found that a s o l u t i o n 0.4N i n H2SO4 and 0.12% i n ammonium molybdate w i l l produce a very s t a b l e complex at room temperature w i t h i n 30 minutes. Absorption i s measured at 866 nm. No i n t e r f e r e n c e s were observed i n the a n a l y s i s of sea water, s i l i c a t e rocks or marine organisms. The a r s e n i c can be separated from the matrix v i a a r s i n e g e n e r a t i o n ^ > ^ , solvent ex52

5 3

5 4

5 5

5

5 8

5

1

1

2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

2.

TALMI AND FELDMAN

19

Traces of Arsenic

2 8

traction63,28,64,65 or c o p r e c i p i t a t i o n with f e r r i c h y d r o x i d e or t h i o n a l i d e ^ . Stara and Stary^b e x t r a c t A s ( I I I ) from s u l f u r i c a c i d s o l u t i o n s f o l l o w i n g conversion to A S I 3 . The compound develops an intense yellow c o l o r when treated w i t h 8-mercaptoquinoline. Procedures were developed to prevent i n t e r f e r e n c e s from the o x i d a t i o n of I to I or from the formation of i n s o l u b l e i o d i d e s . Mankova and Maksiraenko described a method based upon the r e d u c t i o n of AgNO-j to Ag° by AsH . The Ag° exerts a c a t a l y t i c e f f e c t on the f u r t h e r r e d u c t i o n (by F e ) of AgN0 . There i s a r e l a t i o n s h i p between the r e a c t i o n r a t e , measured p h o t o m e t r i c a l l y , and the concent r a t i o n of the c a t a l y s t and thus the c o n c e n t r a t i o n of a r s e n i c . The d e t e c t i o n l i m i t of the r e a c t i o n i s 20 pg/ml. A few workers have developed methods f o r the separate d e t e r mination of a r s e n i t e and arsenate species** »68,62 Spectrophotomeric methods have bee c l u d i n g u r i n e * ^ , blood and atmospheric d u s t . At the present time, spectrophotometry i s s t i l l the most widespread technique f o r the determination of arseni c , mainly because of i t s inherent methodical and t e c h n i c a l simp l i c i t y and i t s low c o s t . 2

67

3

+ 2

3

3

7 2

2.

Radiochemical

Techniques.

A. Among the v a r i o u s radiochemical techniques, neutron a c t i v a t i o n a n a l y s i s (NAA) i s unique i n i t s widespread a p p l i c a b i l i t y to the determination of a r s e n i c . Although, i n p r i n c i p l e , NAA i s a non-destructive a n a l y t i c a l technique, radiochemical s e p a r a t i o n schemes are almost always r e q u i r e d to avoid overlapping of v a r i o u s photo-peaks. Various such schemes "" are based on a combination of two or more s e p a r a t i o n techniques, such as d i s t i l l a t i o n , p r e c i p i t a t i o n , s o l v e n t e x t r a c t i o n or i o n exchange. With the advent of high r e s o l u t i o n s o l i d s t a t e d e t e c t o r s , the d i r e c t instrumental NAA approach has been attempted. Unfortunately, the high a c t i v i t y of N a induced i n many environmentally based samples prevents the determination of a r s e n i c at concentrations below a few ppm, s i n c e the y - a c t i v i t y of these samples w i l l have to decay f o r 4-5 days before measurement. The induced y - a c t i v i t y of i s measured by monit o r i n g the 559 KeV photopeak. T h i s peak w i l l appear, i n many samp l e s , as the middle peak of a t r i p l e t composed of B r ( t / = 35.3h), A s ( t y = 26.5h) and S b ( t , / = 67.2h) r e q u i r i n g the r e s o l u t i o n performance obtained by Ge(Li) d e t e c t o r s . A l s o , s i n c e A s has the s h o r t e s t h a l f - l i f e i n the t r i p l e t , the counting should be done as soon as p o s s i b l e a f t e r i r r a d i a t i o n . NAA i s one of the most s e n s i t i v e techniques with a d e t e c t i o n l i m i t of 0.1 ng using a thermal neutron f l u x of 1 0 ~ neut.-cnT-^-sec" . The method i s u s e f u l at the sub-ppm concentration l e v e l with sample s i z e s s u b s t a n t i a l l y smaller than those r e q u i r e d by the c o l o r i m e t r i c methods. Through the years, NAA has been s u c c e s s f u l l y a p p l i e d to a l a r g e v a r i e t y of samples; b i o l o g i c a l and marine samples' *" , p l a n t t i s s u e s * ^ , water s a m p l e s ^ ^ l ^ i - b o r n e p a r t i c u l a t e m a t t e r ^ , p e s t i c i d e d i s t r i b u t i o n ^ , heavy o i l s p i l l s ^ , g e o l o g i c a l samples >95,96 oal a s h , and many others. P r e c i s i o n and accuracy f o r these samples 73

7

2 4

8 2

1

7 6

2

1 2 2

x

2

2

7

•

•0

*

*

MIXED ACID EXTRACTABLE

•0

• * •

A» to

•

r-0.81 ^-0.66 •

40

QL

Z UJ O

.

0 to

O

cr.

..

-to

"- *

' *

#

*',.

As Soil Science Society of America, Proceedings

Figure 2. A comparison of four methods for the estimation of As availability by a correlation between growth reduction (4-week-old corn) and the log of As concentration in soils (46)

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

44

ARSENICAL PESTICIDES

hot water, IN ammonium c h l o r i d e and 0.5/1? h y d r o c h l o r i c a c i d e x t r a c ted As l e v e l s that were s i g n i f i c a n t l y c o r r e l a t e d with p l a n t growth. Table 3. Levels o f s o i l As a t which s i g n i f i c a n t y i e l d depressions occur. L e v e l o f As a t which Source Crop Soil s i g n i f i c a n t y i e l d deof name type p r e s s i o n s occurred data T o t a l Water A v a i l a b l e As soluble As As - ppm As Colton Blueberry loamy sand Cotton Amarillo f i n —— — _ sandy loam 8 (29) Cotton Houston Black (29) clay 28 Soybean Amarillo f i n e (29) sandy c l a y 3 Soybean Houston Black clay (29) 12 Potatoes, Plainfield — (to) 68 sweet corn loamy sand 22t Snap beans, P l a i n f i e l d — peas loamy sand lot 25 Corn (Avg. o f 13 — 85 soils) 10* 0*6) t E x t r a c t e d with Bray P - l (0.025/7 HCL + 0.3i^ NH F ) # E x t r a c t e d with e i t h e r O.SN NaHC0 o r 0.05/7 HC1 + 0.025/7 ^ S O ^ 3

Table 4. Regression o f a v a i l a b l e a r s e n i c * on t o t a l d r y - p l a n t weight f o r s i x vegetable crops. [Weed Science (32)3 A v a i l a b l e As Regression Correlation at G R * Crop equationt coefficient 50

(r) Green beans y = 77-34 l o g x§ 0.89 0.83 Lima geans y = 107-55 l o g x Spinach y = 88-37 l o g x 0.91 y = 114-38 l o g x 0.80 Cabbage 0.87 Tomato y = 109-42 l o g x 0.81 Radish y = 96-36 l o g x * A v a i l a b l e A s - s o i l extracted with 0.05/7

(ppm) 6.2 10.9 10.6 48.3 25.4 19.0 H SO^ and 0.025/17 HC1

t C a l c u l a t e d by l e a s t squares method 4 GR = a v a i l a b l e s o i l As content necessary t o reduce p l a n t growth t o 50% o f t h a t grown on non-arsenate-treated s o i l § x = a v a i l a b l e s o i l As s

50

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

3. WALSH AND KEENEY

Inorganic Arsenicals in Soil

45

Table 5. C o r r e l a t i o n c o e f f i c i e n t s f o r y i e l d vs. a r s e n i c . [ J o u r n a l o f Environmental Q u a l i t y (29)] Soil

Crop

Amarillo Houston Amarillo Houston

Soybeans Soybeans Cotton Cotton

H0 2

-.943 -.968 -.951 -.954

extractable

Extractant* HCl NH^Cl -.914 -.938 -.960 -.918

-.915 -.931 -.830 -.895

* A l l o f the c o r r e l a t i o n c o e f f i c i e n t s a r e s i g n i f i c a n t a t t h e 0.05 level. Jacobs et_ ajU (40 and the y i e l d s o f s e v e r a P l a i n f i e l d Sand. A l l extractants were n e g a t i v e l y c o r r e l a t e d with crop y i e l d s a t the 0.01 p r o b a b i l i t y l e v e l (Table 6). Total As and ammonium acetate o r Bray P - l e x t r a c t a b l e As were e q u a l l y e f f e c t i v e i n p r e d i c t i n g reduced y i e l d s as l e v e l s o f s o i l As i n creased. Table 6. R e l a t i o n s h i p s between t o t a l o r e x t r a c t a b l e y i e l d o f vegetable crops. [Agronomy J o u r n a l (40)] As fraction

Potatoes

Peas

Crop* Snap beans

s o i l As and

Sweet corn

NH^OAc

-0.91

-0.85

-0.73

-0.91

Bray P - l

-0.91

-0.88

-0.77

-0.93

Total

-0.92

-0.87

-0.76

-0.03

" A l l c o r r e l a t i o n c o e f f i c i e n t s s i g n i f i c a n t a t the 0.01 p r o b a b i l ity level. P r i o r work c l e a r l y i n d i c a t e s that s e v e r a l s o i l t e s t s can be used t o p r e d i c t As p h y t o t o x i c i t y . Even though water s o l u b l e and t o t a l As s a t i s f a c t o r i l y p r e d i c t As p h y t o t o x i c i t y , s o i l t e s t i n g l a b o r a t o r i e s w i l l f i n d i t more convenient t o use Bray P - l , sodium bicarbonate or the mixed a c i d e x t r a c t a n t because these e x t r a c t a n t s a r e now r o u t i n e l y used f o r a v a i l a b l e P. Furthermore, they e x t r a c t more As than water, and e l i m i n a t e the d i g e s t i o n step needed f o r t o t a l As. P l a n t Uptake o f A r s e n i c . A p p l i c a t i o n o f many chemical e l e ments r e s u l t s i n s u b s t a n t i a l increases i n crop a s s i m i l a t i o n o f those elements. In the case o f As such bioaccumulation would be hazardous t o human beings o r animals because o f t o x i c i t y o f As and i t s p o s s i b l e r e l a t i o n s h i p t o cancer, a r t e r e o s c l e r o s i s and c h r o n i c l i v e r diseases (10). F o r t u n a t e l y , the e d i b l e p o r t i o n o f p l a n t s seldom accumulates a hazardous l e v e l o f As, p r i m a r i l y

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

46

ARSENICAL PESTICIDES

because most p l a n t s a r e s e n s i t i v e t o As t o x i c i t y and growth i s u s u a l l y s e v e r e l y reduced b e f o r e a l e v e l o f As hazardous t o man or animals accumulates i n t h e p l a n t . When As poisoning does occur, i t i s u s u a l l y due t o d i r e c t i n g e s t i o n o f a s u r f a c e r e s i d u e o f As or t h e i n g e s t i o n o f s p r i n g water o r muds c o n t a i n i n g abnormally high l e v e l s o f As (50, 51). The e d i b l e p o r t i o n o f most f r u i t s and vegetables grown i n Ast r e a t e d s o i l s c o n t a i n l e s s than the t o l e r a n c e o f 2.6 ppm as a l lowed by the U.S. P u b l i c Health s e r v i c e f o r A s - t r e a t e d f r u i t s and v e g e t a b l e s . The h i g h e s t l e v e l s o f As a r e found i n p l a n t r o o t s , the v e g e t a t i v e top growth i s intermediate, and e d i b l e seeds and f r u i t s c o n t a i n the lowest l e v e l o f As. Jones and Hatch (50) anal y z e d vegetable p l a n t s growing on A s - t r e a t e d s o i l s on s e v e r a l experimental farms i n Oregon and found t h e r o o t s , tops (stems and l e a v e s ) and e d i b l e p o r t i o 1.2 ppm As, r e s p e c t i v e l y (53) observed t h a t vegetables grown on s o i l s t r e a t e d with h i g h l e v e l s o f l e a d arsenate seldom contained more than 1 ppm As i n the e d i b l e p o r t i o n s . A wide range o f forage and vegetable crops were grown by Jones and Hatch (50) on A s - t r e a t e d and adjacent untreated s o i l s i n Oregon. They found the As content i n the e d i b l e p l a n t p a r t s t o be only 1.2 and .41 ppm As i n the t r e a t e d and untreated areas, r e s p e c t i v e l y . On t h e other hand, Small and McCants (3£) found t h a t the c o n c e n t r a t i o n o f As i n f l u e - c u r e d t o bacco v a r i e d from 2 ppm As where no As was a p p l i e d t o 14.3 ppm where 54 kg As/ha or l e a d arsenate had been a p p l i e d t o the s o i l . A r s e n i c l e v e l s o f l e s s than 1.0 ppm were found by Jacobs e t a l . (40) i n potato tubers even where severe As t o x i c i t y occurred. The p e e l i n g , however, contained up t o 48 ppm As where the s o i l had been experimentally t r e a t e d with 720 kg As/ha. The authors suggested the high l e v e l s o f As i n t h e p e e l i n g s was due t o minute q u a n t i t i e s o f As-contaminated s o i l adhering t o the s u r f a c e o f the potato t u b e r , r a t h e r than a s s i m i l a t i o n o f As i n t o the p e e l i n g itself. A survey o f potato grower f i e l d s i n C e n t r a l Wisconsin where 8 t o 65 kg As/ha as sodium a r s e n i t e had been a p p l i e d over a p e r i o d o f s e v e r a l years r e v e a l e d t h a t the potato p e e l i n g s d i d not c o n t a i n more than 2-3 ppm As (54). I t was concluded, thus, t h a t past usage o f sodium a r s e n i t e i n Wisconsin had not caused harmful l e v e l s o f As t o accumulate i n potato tubers. High As l e v e l s have a l s o been observed i n washed, unpeeled r a d i s h e s (32). As with potatoes, p a r t o f the As may have been adsorbed on the s u r f a c e o f the r a d i s h r o o t . Woolson (32) found a s i g n i f i c a n t p o s i t i v e r e l a t i o n s h i p between a v a i l a b l e s o i l As and the c o n c e n t r a t i o n o f As i n the whole p l a n t f o r s i x greenhouse grown vegetable crops (Table 7 ) . Correl a t i o n s between a v a i l a b l e s o i l As and the c o n c e n t r a t i o n o f As i n the e d i b l e p l a n t p a r t s were g e n e r a l l y poorer, e s p e c i a l l y f o r p l a n t s i n which the seed or f r u i t was consumed (32). As p r e v i ously noted, p l a n t s tend t o exclude As from the seeds and f r u i t s . Hence, s o i l t e s t s f o r a v a i l a b l e As would not be a r e l i a b l e

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i n d i c a t o r o f the amount o f As i n the e d i b l e p l a n t t i s s u e . Woolson (32) has pointed out t h a t where the e d i b l e p a r t o f a crop i s not the r o o t or whole p l a n t , i t i s u n l i k e l y t h a t the t o l e r a n c e l e v e l f o r As (2.6 ppm) would be exceeded even where As t o x i c i t y reduced growth by 50%. Table 7. Regression o f a v a i l a b l e s o i l As on the As content i n whole dry p l a n t o r e d i b l e d r y - p l a n t p a r t [Weed S c i . (32] Regression equation

Crop Green bean Lima bean Spinach Cabbage Tomato Radish

y y log y y y log y

= = = = =

Correlation coefficient

0.4 +4.2 l o g x* 0.5 + 1.2 l o -0.12 0. g -0.1 + 3.3 l o g x -0.147 + 1.4 l o g x

(r) 0.93 0.49

(ppm) 3.7t 1.7

0.80 0.88

4.5 43.8

* x = a v a i l a b l e s o i l As t A v a i l a b l e As a t GR_ was used t o c a l c u l a t e As content table 4). n

b

Arsenic a t GR

(see

0

Wherever s o i l s have been t r e a t e d with s u b s t a n t i a l q u a n t i t i e s of As, the surface o f the a e r i a l p o r t i o n o f the p l a n t may be contaminated with dust. The work o f Jacobs e t a l . (40) showed t h a t the concentration o f As i n potato l e a v e s , stems and p e t i o l e s was r e l a t e d t o the surface area o f the p l a n t p a r t s and the p r e v a i l i n g wind i n r e l a t i o n t o p l o t s t r e a t e d with high r a t e s o f As. Plant As c o n c e n t r a t i o n bore l i t t l e r e l a t i o n s h i p t o As treatment; thus, these workers concluded t h a t s u b s t a n t i a l e x t e r n a l contamination of the p l a n t t i s s u e i n the f i e l d had occurred. In l i g h t o f t h i s work, i t appears t h a t some o f the data i n the l i t e r a t u r e on p l a n t uptake o f As would be questionable unless the researcher very c a r e f u l l y washed the p l a n t t i s s u e t o remove adsorbed s o i l p a r t i c l e s . For i n s t a n c e , Jones and Hatch (50) reported t h a t the top growth o f vegetable p l a n t s growing on untreated s o i l adjacent t o As-treated s o i l contained 3.1 ppm As while the r o o t s from these p l a n t s contained only 1.1 ppm As. Since r o o t s normally accumul a t e more As than the top growth, i t appears t h a t the top growth must have been contaminated with s o i l p a r t i c l e s from the adjacent orchard s o i l which had been t r e a t e d with As f o r s e v e r a l years. A l l e v i a t i o n o f As T o x i c i t y Since r e g i s t r a t i o n o f inorganic a r s e n i c a l s f o r use on n e a r l y a l l vegetable and agronomic crops was c a n c e l l e d i n 1968 ( 6 ) , a high p r i o r i t y problem a t the present time i s t o f i n d ways t o r e s t o r e As-contaminated s o i l s t o t h e i r optimal l e v e l o f production (55). Several approaches have been attempted.

American Chemical Society Library In Arsenical Pesticides; Woolson, E.; 1155 16thChemical st. N. Society: w. Washington, DC, 1975. ACS Symposium Series; American l»f_ _L

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.

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ARSENICAL PESTICIDES

Molar P/As Ratio. One approach i s t o add s u f f i c i e n t phosphate t o the system t o depress the uptake o f arsenate by the plant. Hurd-Karrer (37) showed i n s o l u t i o n c u l t u r e work t h a t t h i s hypothesis was v a l i d and that a molar P/As r a t i o o f a t l e a s t 5 was needed t o p r o t e c t against As t o x i c i t y t o wheat. Rumberg et a l . (56) a l s o reported that phosphate w i l l improve growth i n n u t r i e n t s o l u t i o n s containing s u f f i c i e n t arsenate t o be t o x i c . The r e s u l t s with s o i l s systems, however, have been l e s s c l e a r , due i n part t o the d i f f i c u l t y o f evaluating " a v a i l a b l e " P and As. For example, Jacobs and Keeney (35) found that P a d d i t i o n s d i d not i n f l u e n c e As t o x i c i t y on a s i l t loam s o i l . T h i s s o i l had a high P f i x a t i o n c a p a c i t y and a v a i l a b l e P probably d i d not i n crease g r e a t l y . However, with a sandy s o i l , P a c t u a l l y enhanced As t o x i c i t y . The hypothesized t h a t with the sand phosphate may have d i s p l a c e hanced t o x i c i t y . Simila (26) with a sandy loam s o i l . When s u f f i c i e n t phosphate was added to maintain an a v a i l a b l e P/As r a t i o o f about 7, improved y i e l d s r e s u l t e d . T h i s e f f e c t was not c o n s i s t e n t , however, and a t very high l e v e l s o f added As (1,000 ppm), phosphate d i d not overcome As t o x i c i t y even a t a P/As r a t i o o f 10. A d d i t i o n o f Fe o r A l Compounds. Since As i s sorbed by Fe and A l components o f s o i l s , another obvious approach i s t o ammend the s o i l with Fe or A l s a l t s . Large amounts ( 5 t o 10 metric tons/ha) o f f e r r o u s s u l f a t e or f e r r i c s u l f a t e have occas i o n a l l y reduced As t o x i c i t y (57_, 58, 59). Steevens et_ a l . (13) attempted to a l l e v i a t e As t o x i c i t y on a sandy s o i l by a p p l i c a t i o n of 4 metric tons/ha o f f e r r i c s u l f a t e or aluminum s u l f a t e . The Fe treatment had a s l i g h t b e n e f i c i a l e f f e c t while the A l t r e a t ment a c t u a l l y depressed y i e l d s f u r t h e r . Both treatments decreased As uptake by potatoes. C u l t u r a l P r a c t i c e s . Deep plowing t o d i l u t e the As concentrat i o n o f the surface s o i l and expose As t o more s i t e s f o r f i x a t i o n would seem t o be one o f the most economical methods o f decreasing t o x i c i t y . T h i s approach was suggested by McLean e t a l . (53) and A l b e r t (31). Vincent (27) a l s o suggested growing t o l e r a n t cover crops such as r y e or Sudan grass. When plowed under, these crops reduced subsequent As t o x i c i t y . Apparently As t o x i c i t y t o f r u i t t r e e s i s involved with induced Zn d e f i c i e n c y , as f o l i a r a p p l i c a t i o n o f zinc s u l f a t e or Zn chelates w i l l overcome As t o x i c i t y to peach t r e e s (42, 60). Leaching. Woolson et_ a l . (26) pointed out t h a t i n s o i l s i n which added phosphate desorbs arsenate, d e l i b e r a t e leaching o f the s o i l a f t e r a d d i t i o n o f phosphate may be a v i a b l e approach t o removing As from the r o o t zone. This would seem f e a s i b l e s i n c e the l i m i t e d data (13, 26, 35) i n d i c a t e s that phosphate most l i k e l y w i l l desorb arsenate on sandy s o i l s , which a l s o are e a s i e s t

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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to leach since they are very porous. Literature Cited 1.

Kunze, G. W. In "Pesticides and their Effects on Soils and Water," pp. 53-54, ASA Spec. Pub. No. 8, Soil Sci. Amer, Inc., Madison, Wi., 1966.

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Foreback, C. C. "Some Studies on the Detection and Determination of Mercury, Arsenic and Antimony in Gas Discharges," Ph.D. Thesis, Univ. South Florida, 1973.

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In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4 Behavior of Organoarsenicals in Plants and Soils A. E. HILTBOLD Agronomy and Soils Department, Agricultural Experiment Station, Auburn University, Auburn, Ala. 36830

During the past 20 have come into extensive are sodium or ammonium salts of MAA/1 (methanearsonic acid), MSMA (monosodium methanearsonate), DSMA (disodium methanearsonate), and MAMA (monoammonium methanearsonate). The methanearsonates differ from inorganic orthoarsenate in having a methyl substitution of one of the hydroxyl groups linked to the arsenic atom. Replacement of another hydroxyl by a second methyl group produces dimethylarsinic or cacodylic acid (hydroxydimethylarsine oxide). OH OH 0-Na+ i i i 0=As-OH 0=As-CH3 0=As-CH3 &h3 bn3 CH3 MAA Cacodylic acid Na cacodylate OH 0~Na+ OH 0=As-0~Na+ 0=As-0~Na+ 0=As-0"NH4 CH3 CH3 CH3 MSMA DSMA MAMA Figure 1. Formulae of organic arsenical herbicides. Methanearsonic acid is a dibasic acid with pKa values of 3.61 and 8.24 at 18C for dissociation of the first and second OH groups (1). The relative proportion of ionic and molecular forms of methanearsonate is determined by solution pH; Figure 2. At pH 5.93 essentially a l l of the methanearsonate exists as the univalent ion, or in terms of herbicide formulation as MSMA. The undissociated acid (MAA) increases in solution as pH falls below 5.93 and the proportion of univalent ion decreases. Solutions of MAA are acid, about pH 2. With increasing pH from 5.93 the divalent ion (DSMA) increases in proportion. DSMA solutions are aklaline, about pH 10.5. .1/Abbreviations used in the text are the common names of these herbicides accepted by the Weed Science Society of America. 53

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ARSENICAL PESTICIDES

54

Cacodylic a c i d has a s i n g l e a c i d i c OH; pK =6.19 a t 25C (I). The p r o p o r t i o n o f i o n i c form increases from near zero a t pH 4.0 to e s s e n t i a l l y 100% a t pH 8.5, Figure 3. Cacodylic a c i d s o l u t i o n s are m i l d l y a c i d i c while Na cacodylate s o l u t i o n s are m i l d l y a l k a l i n e . While v a r i o u s a c i d or s a l t formulations o f these organoars e n i c a l s may be a p p l i e d , t h e i r chemical form i n s o i l s o l u t i o n i s determined by the e x i s t i n g pH. In most a g r i c u l t u r a l s o i l s with pH values i n the range pH 5.0 t o 7.0 the u n i v a l e n t i o n of methanearsonate predominates almost to the e x c l u s i o n o f the u n d i s s o c i a t e d or d i v a l e n t forms. Both cacodylate i o n and a c i d may occur i n s o i l s , with the a c i d form predominant a t pH6.2. a

H e r b i c i d a l P r o p e r t i e s and Use Patterns MSMA, DSMA, and MAM marketed a l s o as a white, c r y s t a l l i n e powder. Cacodylic a c i d may be obtained i n c r y s t a l l i n e form o r i n mixture with Na cacodylate as a l i q u i d . A l l of these products are h i g h l y s o l u b l e i n water. They are a p p l i e d with s u r f a c t a n t as sprays to the f o l i a g e of weeds. Theyhave no preemergence a c t i v i t y a t r a t e s used f o r weed c o n t r o l . Methanearsonates are used most e x t e n s i v e l y f o r postemergence c o n t r o l o f annual grass weeds i n c o t t o n (Gossypium hirsutum L . ) . A c t i v i t y of the methanearsonates on johnsongrass [(Sorghum h a l e pens e (L.) Pers.)] purple nutsedge (Cyperus rotundus L . ) , and yellow nutsedge (Cyperus esculentus L.) makes these h e r b i c i d e s an important part of the weed c o n t r o l program i n cotton. Substantial c o n t r o l o f these weeds i s provided by the methanearsonates (2), but repeated a p p l i c a t i o n s are u s u a l l y r e q u i r e d . MSMA i s r e g i s tered f o r use i n cotton a t 2.2 to 2.8 kg/ha and DSMA at 2.2 t o 3.4 kg/ha. In order to avoid i n j u r y o f cotton and a r s e n i c (As) r e s i dues i n cottonseed, use i s r e s t r i c t e d to the stage between the time when p l a n t s are about 10 cm t a l l and when they f i r s t bloom (3). Sprays must be d i r e c t e d to cover small weeds i n the d r i l l row but minimize contact with cotton leaves. S e l e c t i v e c o n t r o l of crabgrass ( D i g i t a r i a s a n g u i n a l i s (L.) Scop, and D. ischaemum (Schreb.) Muhl.) and d a l l i s g r a s s (Paspalum d i l a t a t u m P o i r . ) i n e s t a b l i s h e d t u r f i s provided by the methanearsonates with minimal i n j u r y of most t u r f g r a s s s p e c i e s . Nutsedge i s more p e r s i s t e n t but may be e f f e c t i v e l y c o n t r o l l e d with repeated a p p l i c a t i o n s o f 4 kg/ha (4). Methanearsonates are a l s o widely used i n non-crop areas f o r c o n t r o l of johnsongrass and v a r i o u s weeds on rights-of-way, along d i t c h banks, e t c . Cacodylic a c i d and Na cacodylate are n o n - s e l e c t i v e , f o l i a r contact-type h e r b i c i d e s (_5). Use i s r e s t r i c t e d t o non-crop areas where they are u s e f u l i n c o n t r o l l i n g many herbaceous and woody s p e c i e s . Rates r e q u i r e d f o r e f f e c t i v e c o n t r o l range from 3 t o 5 kg/ha and may be repeated as necessary. Tree i n j e c t i o n with cacod y l i c a c i d provides s e l e c t i v e e l i m i n a t i o n of undesirable s p e c i e s i n e s t a b l i s h e d stands. Cacodylic a c i d i s a l s o used i n t u r f g r a s s

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

HILTBOLD

Figure 2.

Organoarsenicals in Plants and Soils

Per cent total methanearsonate as the univalent ion

'4.0

4.5

5.0

5.5

6.0

6.5

7.0

7.5

CH AsO(OH)0~ 3

8.0 8.5

PH Figure 3.

Per cent total cacodylate as the univalent ion (CH. ) AsO {

2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

O'

ARSENICAL PESTICIDES

56

renovation f o r complete k i l l of e x i s t i n g vegetation p r i o r t o r e seeding the d e s i r e d species. The i n a c t i v a t i o n of c a c o d y l i c a c i d i n s o i l and i t s l a c k of r e s i d u a l p h y t o t o x i c i t y are advantages. Behavior of Organoarsenicals

i n Plants

Organic a r s e n i c a l h e r b i c i d e s are intended f o r i n t e r c e p t i o n by weed f o l i a g e r a t h e r than by s o i l as would be the case with a preemergence-type h e r b i c i d e . The f r a c t i o n of the a p p l i e d h e r b i c i d e i n t e r c e p t e d by f o l i a g e v a r i e s widely with weed density and spraying c o n d i t i o n s . The extent to which the i n t e r c e p t e d f r a c t i o n i s absorbed, t r a n s l o c a t e d , and metabolized may i n f l u e n c e the amount and chemical form o f the m a t e r i a l that u l t i m a t e l y reaches the s o i l An understanding o f the f a t e of an h e r b i c i d e i n p l a n t s may provide u s e f u l background f o r i t Absorption. While organoarsenicals may be absorbed by roots of johnsongrass (6), Coastal bermudagrass [Cynodon dactylon (L.) Pers.] (7), and bean (Phaseolus v u l g a r i s L.) (8) i n s o l u t i o n c u l ture, root uptake from s o i l i s d r a s t i c a l l y reduced (7). The p r i mary pathway o f entry i n t o p l a n t s i s through the leaves and stems. Duble, H o l t , and McBee (7) compared uptake of As by Coastal bermudagrass from s e v e r a l sources of a p p l i c a t i o n of DSMA, Figure 4. A p p l i c a t i o n to f o l i a g e was at 4.5 kg/ha, to s o i l a t 17.9 kg/ha, and to roots i n n u t r i e n t s o l u t i o n a t 12 ppm. Absorption u s u a l l y occurs w i t h i n s e v e r a l hours a f t e r a p p l i c a t i o n (9). Keeley and T h u l l e n (10) found that exposure of yellow nutsedge leaves to MSMA and DSMA f o r as l i t t l e as 5 and 15 minutes, r e s p e c t i v e l y , c o n t r o l l e d t h i s weed. However, 24- and 48-hr exposures were required f o r c o n t r o l of purple nutsedge. Surfactants are r o u t i n e l y included i n spray s o l u t i o n s to increase coverage and enhance absorption. McWhorter (11) found that increases i n p h y t o t o x i c i t y of DSMA to johnsongrass r e s u l t i n g from added s u r f a c t a n t were greatest a t low r a t e s o f DSMA near th~ margin f o r weed c o n t r o l . S i m i l a r l y , Keeley and T h u l l e n (10) observed improved c o n t r o l of regrowth of purple nutsedge f o l l o w i n g f o l i a r a p p l i c a t i o n of DSMA with s u r f a c t a n t , Table I. The l a r g e r responses to s u r f a c t a n t were obtained a t the low r a t e of DSMA and at the high temperature. Apparently s u r f a c t a n t s f a c i l i t a t e entry of methanearsonate i n t o the t r e a t e d l e a f ; then, with temperature favorable f o r growth, the h e r b i c i d e i s t r a n s l o c a t e d to c r i t i c a l sites. In cotton, however, severe i n j u r y from t o p i c a l a p p l i c a t i o n of MSMA occurred a t low (13C) temperature but not a t 31C, a more favorable temperature f o r growth. This i n j u r y was aggravated by s u r f a c t a n t (12). There i s evidence of greater absorption of MSMA than o f DSMA. When equal amounts of MAA, MSMA, and DSMA were a p p l i e d to c o t y l e dons of young cotton, Keeley and T h u l l e n (12) found that absorpt i o n of MAA and MSMA was s e v e r a l f o l d greater than that of DSMA. In the f i e l d , t o p i c a l a p p l i c a t i o n s of MSMA were more i n j u r i o u s to

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.68 1.68 3.36 3.36 1.68 1.68 3.36 3.36

DSMA DSMA DSMA DSMA MSMA MSMA MSMA MSMA

Herbicide

Table I .

QO)

none 0.5% none 0.5% none 0.5% none 0.5%

Surfactant

100 99 89 54 12 1 7 0

14 0 0 0 0 0 0 0

66 77 40 21 48 17 6 0

27 16 12 0 4 5 0 0

84 12 77 20 31 32 5 1

Weed Science

0 0 0 0 0 0 0 0

Temperature 13C 20C 29C Purple Yellow Purple Yellow Purple Yellow (Fresh weight as % o f c o n t r o l )

Following a F o l i a r A p p l i c a t i o n of DSMA o r MSMA t o P l a n t s Grown a t Various Temperatures

Regrowth o f Purple and Yellow Nutsedge (% Fresh Shoot Weight o f the C o n t r o l ) 3 Weeks

ARSENICAL PESTICIDES

58

FOLIAGE

REGROWTH

SOLUTION

SOURCE

OF DSMA

SOIL

J o u r n a l of A g r i c u l t u r a l and Food Chemistry Figure 4. D i s t r i b u t i o n o f As i n Coastal bermudagrass 7 days a f t e r f o l i a r , n u t r i e n t s o l u t i o n , and s o i l a p p l i c a t i o n s o f DSMA. Regrowth from a f o l i a r a p p l i c a t i o n represented 3 weeks growth a f t e r c l i p p i n g to ground l e v e l 7 days a f t e r treatment (!>• cotton than equal r a t e s o f DSMA, and the d i f f e r e n c e became more pronounced with higher a p p l i c a t i o n r a t e s and l a t e r stages o f growth (13). Temperature may a l s o i n f l u e n c e the r e l a t i v e absorpt i o n of MSMA and DSMA. In purple nutsedge growing at29C, absorption of MSMA and DSMA d i d not d i f f e r , but a t 13 and 20C absorption o f MSMA exceeded that o f DSMA (10). An explanation o f the d i f f e r e n t i a l absorption o f the methanearsonates may l i e i n the pH o f t h e i r s o l u t i o n s , t h e i r predominant i o n i c or molecular s p e c i e s , and the p e r m e a b i l i t y of l e a f membranes t o these s p e c i e s . The evidence suggests that the u n d i s s o c i a t e d a c i d or u n i v a l e n t i o n penetrates more r e a d i l y than the d i v a l e n t i o n . P l a n t species d i f f e r i n t h e i r s e n s i t i v i t y t o methanearsonates, probably due i n p a r t to d i f f e r e n c e s i n p e r m e a b i l i t y o f l e a f surf a c e s . Leaves of yellow nutsedge have been found to be more permeable t o these h e r b i c i d e s than those o f purple nutsedge (10). The t o l e r a n c e shown by cotton and many t u r f g r a s s e s f o r methanearsonates i s fundamental t o the use of these h e r b i c i d e s f o r s e l e c t i v e weed c o n t r o l . The b a s i s f o r t h i s t o l e r a n c e i s not y e t c l e a r . Tolerance among plant species i s r e l a t i v e , however, as evidenced by severe

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4.

HILTBOLD

Organoarsenicals in Plants and

Soils

i n j u r y of cotton from f o l i a r a p p l i c a t i o n s at bloom stage

59 (3).

T r a n s l o c a t i o n . H e r b i c i d e movement out of the t r e a t e d t i s s u e and i n t o more c r i t i c a l s i t e s of a c t i v i t y i s e s s e n t i a l i f the h e r b i c i d e i s to f u n c t i o n more than as a desiccant. The s u p e r i o r i t y of methanearsonates over contact type h e r b i c i d e s such as Na a r s e n i t e i s due i n part to t h e i r more extensive t r a n s l o c a t i o n (8, 9). Compared to amounts that may be present i n t r e a t e d t i s s u e , however, r e l a t i v e l y small amounts are t r a n s l o c a t e d to other p l a n t p a r t s . In soybean [Glycine max (L.) Merr.] and crabgrass, Rumber& Engel, and Meggitt (9) found that l e s s than 2% of the DSMA recovered 6 hr a f t e r a p p l i c a t i o n to the leaves was t r a n s l o c a t e d i n t o other p l a n t p a r t s . Sachs and Michael (8) reported that 6% of the MSMA absorbed i n t r e a t e d leaves of bean was t r a n s l o c a t e d during a 3-day p e r i o d . In purpl DSMA was moved out of th C o a s t a l bermudagrass, 24% of the a p p l i e d DSMA was t r a n s l o c a t e d from t r e a t e d leaves to other plant parts i n a 5-day p e r i o d (7). D i f f i c u l t y of o b t a i n i n g adequate t r a n s l o c a t i o n of methanearsonates to johiBongrass rhizomes (11) and nutsedge tubers (14, 15) makes repeated a p p l i c a t i o n s necessary. Increasing temperature w i t h i n the range favorable f o r growth g e n e r a l l y a c c e l e r a t e s t r a n s l o c a t i o n of methanearsonate. Rumberg et a l . (9) reported more r a p i d t r a n s l o c a t i o n of DSMA at 30C than at 15C i n soybean and crabgrass. The increased t r a n s l o c a t i o n was a l s o a s s o c i a t e d with increased p h y t o t o x i c i t y of DSMA to crabgrass. S i m i l a r l y , movement of methanearsonate from t r e a t e d nutsedge p l a n t s i n t o daughter p l a n t s was found to be greater at 29C than at 13C (10). In cotton, contact i n j u r y of cotyledons by MSMA may preclude t r a n s l o c a t i o n to the leaves and terminal bud, sparing the plant severe i n j u r y . At low temperature (13C), however, cont a c t i n j u r y was n e g l i g i b l e and MSMA t r a n s l o c a t i o n exceeded that at 31C, r e s u l t i n g i n s t u n t i n g or death of the p l a n t (12). Both a c r o p e t a l and b a s i p e t a l t r a n s l o c a t i o n moves methanearsonate out of t r e a t e d leaves of johnsongrass (6), nutsedge (10, 14), bean (8), Coastal bermudagrass (7), soybean and crabgrass (9). S c k e r l and Frans (6) observed very l i t t l e b a s i p e t a l movement of methanearsonate i n cotton, although f o l i a r and stem a p p l i c a t i o n moved a c r o p e t a l l y . B a s i p e t a l movement of methanearsonate to rhizomes and tubers i s c r i t i c a l to the c o n t r o l of hardy p e r e n n i a l s such as johnsongrass and nutsedge. Methanearsonate a p p l i e d to nutsedge shoots i s t r a n s l o c a t e d to newly developing rhizomes, shoots, and tubers as i n d i c a t e d by phytotoxic r e a c t i o n and As determination (14, 16). Accumulation of As i n these a c t i v e growth s i t e s suggests that meristematic t i s s u e s are the major p o i n t s of herbicidal activity. Metabolism. There i s no evidence of s u b s t a n t i a l degradation of rupture of the C-As bond of organoarsenicals i n p l a n t s . MSMAderived CO2 i n the r e s p i r a t o r y CO2 of t r e a t e d Coastal bermudagrass

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL PESTICIDES

60

and purple nutsedge leaves amounts to a small f r a c t i o n o f the h e r b i c i d e i n the t i s s u e (7, 14)• Cacodylic a c i d i s apparently a very s t a b l e compound i n bean p l a n t s ; chromatographic a n a l y s i s showed l i t t l e i f any As a s s o c i a t e d with any f r a c t i o n other than c a c o d y l i c a c i d i t s e l f (8). E x t r a c t s o f MSMA-treated bean, however, revealed two As-containing f r a c t i o n s : parent MSMA and an u n i d e n t i f i e d complex of MSMA with some plant component (8). Simil a r complexes have been observed i n johnsongrass a f t e r treatment with MAA (6) and C o a s t a l bermudagrass a f t e r a p p l i c a t i o n o f DSMA (7). Radioassay and As a n a l y s i s o f the DSMA complex v e r i f i e d the p e r s i s t e n c e of the C-As bond (7). The mechanism o f p h y t o t o x i c i t y of the organoarsenicals i s not known. C r i t i c a l l e v e l s o f As r e q u i r e d f o r c o n t r o l o f regenerative p a r t s such as nutsedge tubers have not been e s t a b l i s h e d (16). Behavior o f Organoarsenical Much of the spray t;hat i s not i n t e r c e p t e d by f o l i a g e i s deposited d i r e c t l y on the s o i l . In a d d i t i o n , much o f that which i s i n t e r c e p t e d by weeds reaches the s o i l i n d i r e c t l y when r a i n washes l e a f surfaces o r k i l l e d v e g e t a t i o n decays. While methanearsonate or cacodylate may be a p p l i e d i n a c i d o r s a l t form, once i n the s o i l the predominant i o n i c o r molecular form i s determined by s o i l s o l u t i o n pH. In most s o i l s (pH 5 to 7) the u n i v a l e n t i o n of methanearsonate i s the dominant form. Cacodylate e x i s t s i n approximately equal concentrations o f u n d i s s o c i a t e d a c i d and cacod y l a t e i o n i n moderately a c i d s o i l s . Adsorption. Much o f the r e d u c t i o n i n a c t i v i t y o f organoarsen i c a l s upon reaching the s o i l i s a t t r i b u t a b l e to adsorption by s o i l c o l l o i d s . When s o l u t i o n s o f DSMA, Na cacodylate, arsenate, and phosphate were e q u i l i b r a t e d with 16 s o i l s , Wauchope (17) found that adsorption by i n d i v i d u a l s o i l s increased i n the order: phosphate Na2HAs04, DSMA, Na cacodylate, and Na propylarsonate. Trimethylarsine [(CH3)3As] was the most common gaseous product. I n a l l cases, As was reduced to the t r i v a l e n t s t a t e and a l l s u b s t i tuent oxygen atoms replaced by methyl groups. With methanearsonate, cacodylate, and propylarsonate, the evolved a r s i n e contained the o r i g i n a l a l k y l i n t a c t : t r i m e t h y l a r s i n e and dimethy1-n-prop y l a r s i n e . The mechanism proposed by Challenger (27) was a stepwise r e d u c t i o n and methylation of arsenate through a r s e n i t e , methanearsonate, and cacodylate to the completely reduced and methylated t r i m e t h y l a r s i n e . Recently, Cox and Alexander (28) i s o l a t e d species o f Candida, Gliocladium, and P e n i c i l l i u m producing t r i m e t h y l a r s i n e from a r s e n i c a l s i n c l u d i n g MAA and c a c o d y l i c a c i d . The only evidence of b a c t e r i a methylating As i s that o f McBride and Wolfe (29), r e p o r t i n g the synthesis o f dimethylarsine by the anaerobe Methanobacterium. I n t h i s mechanism the i n t e r mediate c a c o d y l i c a c i d was reduced d i r e c t l y to dimethylarsine without the f i n a l methylation. The extensive v o l a t i l i z a t i o n of As from c a c o d y l i c a c i d - t r e a t e d s o i l s (20) when incubated anaerobic a l l y would n e c e s s a r i l y i m p l i c a t e b a c t e r i a such as Methanobacterium. Under aerobic c o n d i t i o n s , f u n g i appear to be the a c t i v e microorganisms. As

Persistence. Loss o f p h y t o t o x i c i t y with time a f t e r a p p l i c a t i o n o f organoarsenicals to s o i l may be viewed as a measure of p e r s i s t e n c e . Results of Schweizer (22) and Ehman (23) i n d i c a t e

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4. HILTBOLD

Organoarsenicals in Plants and Soils

65

extensive i n a c t i v a t i o n and d i m i n i s h i n g e f f e c t s on subsequent crops. Y i e l d s o f a v a r i e t y o f f i e l d crops were u n a f f e c t e d by r e s i d u e s o f methanearsonate equivalent t o 68 kg As/ha a p p l i e d during the previous 4 years (24). S i m i l a r l y , y i e l d s o f cotton were u n a f f e c t e d by 6 annual p r e p l a n t a p p l i c a t i o n s o f MSMA at 10, 20, and 40 kg/ha (19). On the other hand, Singh and Campbell (30) found that both DSMA and MAMA, when a p p l i e d to t u r f a t r a t e s o f 5.0 and 4.5 kg/ha, r e s p e c t i v e l y , twice annually f o r 2 years, pers i s t e d i n the upper 5 cm of a s i l t loam s o i l i n amounts s u f f i c i e n t to i n j u r e oats (Avena s a t i v a L.) and soybeans, as shown by b i o assay o f s o i l 9 months a f t e r the l a s t a p p l i c a t i o n . Estimates of the r a t e of methanearsonate o x i d a t i o n t o CO2 and i n o r g a n i c arsenate are provided by s o i l incubations with 1Rel a b e l e d methanearsonate (JJS, 25) I n l i g h t t e x t u r e s o i l s of low organic matter content estimate of o x i d a t i o n and l a r g e r m i c r o b i a l p o p u l a t i o n s , about 10% per month may be o x i d i z e d . I f these r a t e s remain constant, as would be the case i n a f i r s t - o r d e r r e a c t i o n , the amount o f r e s i d u a l methanearsonate at any time a f t e r a p p l i c a t i o n may be c a l c u l a t e d . A f i r s t - o r d e r f u n c t i o n appears to be the simplest and most r e a l i s t i c representat i o n o f methanearsonate metabolism i n s o i l . T h i s i s supported by the o b s e r v a t i o n o f equal percentage l o s s e s among widely d i f f e r i n g r a t e s o f a p p l i c a t i o n (20, 25). Moreover, the general l a c k o f m i c r o b i a l response to added methanearsonate (18, 25) suggests a p a s s i v e degradation dependent p r i m a r i l y upon c o n c e n t r a t i o n . T h i s c o n t r a s t s with the degradation o f the phenoxyalkanoic acid h e r b i c i d e s , f o r example. With these, m i c r o b i o l o g i c a l adaptation occurs, r e s u l t i n g i n r a p i d l y a c c e l e r a t e d decomposition, e l i m i n a t i o n o f the l a g p e r i o d , and development o f the enrichment e f f e c t (31). The f i r s t - o r d e r r a t e law may be expressed k

=

^

l

o

g

as f o l l o w s :

^ and ^ = ^ 9 3

where:

k = r a t e constant t = time C = i n i t i a l concentration C = c o n c e n t r a t i o n a t time t tjg = h a l f - l i f e o f decomposition S u b s t i t u t i n g and s o l v i n g f o r 2 and 10% decomposition per month y i e l d s values o f 0.7847 and 0.2827, r e s p e c t i v e l y , f o r conc e n t r a t i o n s remaining 1 year a f t e r a p p l i c a t i o n o f u n i t concentrat i o n of methanearsonate. H a l f - l i v e s corresponding t o 2 and 10% per month l o s s r a t e s are 34.31 and 6.58 months, r e s p e c t i v e l y . The r e s i d u e o f N annual a d d i t i o n s i s given by the equation (32): Q

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

66

ARSENICAL PESTICIDES

r = 1+ f

+ fj 2 + f 3 +

l

x

Co \C J°>

l -

0

f

l

where:

f i = f r a c t i o n l e f t a f t e r one year r * accumulated r e s i d u e , immediately a f t e r a d d i t i o n of annual increment/ % The l i m i t of the maximum amount of r e s i d u e s — J i s given by the expression J _ . The r e s i d u e p a t t e r n f o r annual a d d i t i o n s o f i 1 ppm MSMA-As i s given i n Figure 6, assuming f i r s t - o r d e r decompos i t i o n to i n o r g a n i c arsenate a t 10% per month (above) and 2% per month (below). No l o s s e s o f As from the s o i l a r e considered Annual a p p l i c a t i o n o f mately that provided b at 2.5 kg/ha each. At the higher decomposition r a t e the maximum amount of r e s i d u a l MSMA i s 1.39 ppm and i s approached a f t e r sever a l a p p l i c a t i o n s . Residual MSMA i n t h i s s i t u a t i o n remains a t very low l e v e l s and the p r i n c i p a l product accumulating i s a r s e nate. At the low r a t e of decomposition the maximum amount of r e s i d u a l MSMA i s 4.64 ppm and i s approached a f t e r 30 annual a d d i t i o n s . At t h i s time the s o i l residues would be 15% as MSMA and 85% as arsenate. The foregoing estimates o f residue accumulation do not take i n t o account l o s s e s of As from the s o i l . F i e l d experiments (19, 24) i n d i c a t e l o s s o f As from s o i l during periods o f repeated a p p l i c a t i o n o f methanearsonate. In s i t u a t i o n s where l o s s of As i n s o i l e r o s i o n and crop removal were n i l , approximately 40 to 60% of the As a p p l i e d as methanearsonate was unaccounted f o r i n t o t a l As determinations of the s o i l . These r e s u l t s suggest a gaseous l o s s process of considerable important with regard to r e s i d u e accumulation. P r e f e r e n t i a l methylation and v o l a t i l i z a t i o n of methanearsonate would f u r t h e r reduce r e s i d u a l concentrat i o n s and a l t e r the p r o p o r t i o n of methanearsonate and arsenate. 00

f

l

Uptake o f As by Crops. The l i t e r a t u r e d e a l i n g with i n o r g a n i c As i n s o i l s and crops shows that p l a n t s g e n e r a l l y absorb and t r a n s l o c a t e r e l a t i v e l y s m a l l amounts of As. L i t t l e i n f o r m a t i o n i s a v a i l a b l e on the appearance of As residues i n crops r e s u l t i n g from root a b s o r p t i o n of methanearsonate or methanearsonate-der i v e d As. Ehman (23) reported s i g n i f i c a n t l e v e l s o f As i n s e v e r a l f i e l d crops planted immediately a f t e r a p p l i c a t i o n of DSMA to s o i l , but r a t e s of 35 kg/ha o r more were r e q u i r e d . Johnson and H i l t b o l d (24) reported As residues i n f i e l d crops grown on p l o t s r e c e i v i n g methanearsonate a p p l i c a t i o n s during the previous 4 years. Cottonseed and soybeans contained higher l e v e l s of As than corn (Zea mays L.) g r a i n o r v e g e t a t i v e m a t e r i a l o f sorghumsudan h y b r i d (Sorghum vulgare Pers. X Sudanense (Piper) Stapf.). Cool-season forages accumulated l e s s As than summer crops.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

HILTBOLD

Organoarsenicals in Plants and Soils

Figure 6. Residue pattern for annual additions of 1 ppm MSMA-As first-order half-life of 6.58 mo (top) and 34.31 mo (bottom)

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

and

68

ARSENICAL PESTICIDES

Later experiments (19) with soil applications of MSMA at elevated rates preplant to cotton over a 6-year period failed to show As residues in cottonseed grown on 3 soil types. Sustained used of methanearsonates at rates recommended for weed control does not appear to result in hazardous accumulation of As in harvested crops. Methanearsonates are extensively adsorbed in soil and subject to l i t t l e movement in leaching. Loss from treated fields may occur where erosion is severe. Volatilization of methylated As appears to be a significant loss process that limits As accumulation in soil and probably accounts for the ubiquitous occurrence of As in soils generally. The organoarsenicals are oxidized microbiologically producing arsenate. While arsenate is subject to methylation and volatile loss, much of the residual As in soil reverts to progressively less soluble forms with aluminum and iron compounds. Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20.

Sillen, L. G., Martell, A. E . , "Stability Constants of Metal-Ion Complexes" Second Edition, P. 206. Chemical Society, London, 1964. Widiger, R. E., Proc. S. Weed Conf. (1966) 19, 51-56. Baker, R. S., Arle, H. F., Miller, J. H., Holstun, J. T. Jr., Weed Sci. (1969) 17, 37-40. Long, J. A., Allen, W. W., Holt, E. C., Weeds (1962) 10, 285-287. Stevens, G. D., Proc. S. Weed Conf. (1966) 19, 545-549. Sckerl, M. M., Frans, R. E . , Weed Sci. (1969) 17, 421-427. Duble, R. L., Holt, E. C., McBee, G. G., J. Agr. Food Chem. (1969) 17, 1247-1250. Sachs, R. M., Michael, J. L., Weed Sci. (1971) 19, 558564. Rumburg, C. B., Engel, R. E . , Meggitt, W. F., Weeds (1960) 8, 582-588. Keeley, P. E . , Thullen, R. J., Weed Sci. (1971) 19, 601606. McWhorter, C. G., Weeds (1966) 14, 191-194. Keeley, P. E . , Thullen, R. J., Weed Sci. (1971) 19, 297300. Arle, H. F., Hamilton, K. C., Weed Sci. (1971) 19,545-547. Duble, R. L . , Holt, E. C., McBee, G. G., Weed Sci. (1968) 16, 421-424. Hamilton, K. C., Weed Sci. (1971) 19, 675-677. Holt, E. C., Faubion, J. L . , Allen, W. W., McBee, G. G., Weeds (1967) 15, 13-15. Wauchope, R. D., Proc. S. Weed Sci. Soc. (1974) 27, 389. Dickens, Ray, Hiltbold, A. E . , Weeds (1967) 15, 299-304. Hiltbold, A. E., Hajek, B. F., Buchanan, G. A . , Weed Sci. (1974) 22, 272-275. Woolson, E. A . , Kearney, P. C., Environ. Sci. Technol.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

4.

HILTBOLD

21. 22. 23. 24. 25. 26. 27. 28. 29. 30. 31. 32.

Organoarsenicals in Plants and Soils

69

(1973) 7, 47-50. Jacobs, L. W., Syers, J. K., Keeney, D. R., Soil Sci. Soc. Amer. Proc. (1970) 34, 750-754. Schweizer, E. E . , Weeds (1967) 15, 72-76. Ehman, P. J., Proc. S. Weed Conf. (1965) 18, 685-687. Johnson, L. R., Hiltbold, A. E. Soil Sci. Soc. Amer. Proc. (1969) 33, 279-282. Von Endt, D. W., Kearney, P. C., Kaufman, D. D., J. Agr. Food Chem. (1968) 16,17-20. Thom, C., Raper, K. B., Science (1932) 76, 548-550. Challenger, F., Chem. Rev. (1945) 36, 315-361. Cox, D. P., Alexander M., Bull. Env. Cont. Tox. (1973) 9, 84-88. McBride, B., Wolfe, R., Biochem. (1971) 10, 4312-4317. Singh, R. K. N . 171. Audus, L. J., Plant and Soil (1951) 3, 170-192. Hamaker, J. W., Advan. Chem. Ser. (1966) 60, 122-131.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

5 Arsenicals in Animal Feeds and Wastes C. C. CALVERT Biological Waste Management Laboratory, Agricultural Environmental Quality Institute, Agricultural Research Service, Department of Agriculture, Beltsville, Md. 20705 Since arsenic trioxid ing over 4000 years ago of medicinal purposes (1). The modern era of arsenic use in medicine began with the characterization of arsanilic acid by Erlich and Bertheim in 1907 (2) and was extended more recently by the discovery in 1945 by Morehouse and Mayfield (3) that an organic arsenical, 3-nitro-4-hydroxyphenylarsonic acid commonly called (3-nitro), could be used to control coccidiosis and promote growth in chicks. Since that time, other organic arsenicals such as arsenosobenzene, arsanilic acid, 4-nitrophenylarsonic acid and p-ureidobenzenearsonic acid have been shown to have both therapeutic and growth-promotant properties as feed additives for poultry and swine. At the present time, a l l of these compounds, with the exception of arsenosobenzene, are approved by the U.S. Food and Drug Administration for use in poultry and swine feeds but only at levels low enough to preclude residues in edible animal tissue which would be a hazard to human health. The objective of this discussion will be to review briefly the efficacy of these arsenic compounds with respect to animal production, the absorption and excretion of these arsenicals when fed to animals and, finally, the fate of arsenic in animal excreta. Arsenicals in Swine and Poultry Feeds Table 1 shows the chemical structure of 4 arsenicals currently approved for use as growth promotants or therapeutic agents, or both, in poultry and swine feeds. The arsenic in a l l these compounds is pentavalent. Changing the substituents on the ring changes the growth-promoting and anti-parasite effects of the compound. Note that arsanilic acid and 3-nitro are approved for both poultry and swine, whereas 4-nitrophenylarsonic acid and p-ureidobenzenearsonic acid are approved only for turkeys. The use of these compounds in turkeys is limited to feeding for therapeutic purposes and may not be used as growth promotants (4). 70

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

5.

CALVERT

71

Animal Feeds and Wastes

Table 1.

Chemical s t r u c t u r e of a r s e n i c a l s used i n animal feeding As 0 (OH), As 0 (OH),

0

N0 NH.

OH 3-nitro-4-hydroxyphenylarsonic A c i d (Poultry & Swine)

A r s a n i l i c Acid (Poultry & Swine) As 0 ( 0 H )

o

n

As 0 ( 0 H )

o

o

NO,

4-nitrophenylarsonic (Turkeys)

Acid

p-ureidobenzenearsonic A c i d (Turkeys)

The FDA has e s t a b l i s h e d l e v e l s a t which these compounds may be used i n animal feeds, and i t has a l s o determined the maximum l e v e l s of a r s e n i c that may be present i n marketed p o u l t r y and swine. These maximum use l e v e l s and maximum t i s s u e l e v e l s are shown i n Table 2. In order that these t i s s u e l e v e l s may be met, the user of a r s e n i c a l - c o n t a i n i n g feed i s r e q u i r e d by FDA regul a t i o n s to withdraw the a r s e n i c - c o n t a i n i n g feed f o r a t l e a s t 5 days before slaughter. Growth Response from the Use o f A r s e n i c a l s Many experiments have expanded on the o r i g i n a l demonstration of the e f f i c a c y of 3 - n i t r o and other a r s e n i c a l s i n both p o u l t r y and swine r a t i o n s . No attempt w i l l be made i n t h i s d i s c u s s i o n to cover a l l of the research that has been conducted with the a r s e n i c a l s i n feed, but a few examples of the types o f responses obtained w i l l be presented. A number of reviews on t h i s subject are i n the l i t e r a t u r e and should be consulted f o r more d e t a i l e d information (5-9.). Baron (9), a t a symposium i n London i n 1969, presented examples of the type of responses that may be obtained by feeding a r s e n i c a l s to growing chickens. Results of a study i n which 3- n i t r o was f e d i n 15 t r i a l s to a t o t a l of 1148 b i r d s f o r a 4-week p e r i o d are shown i n Table 3. As can be seen i n t h i s t a b l e , the average response i n weight increase due to a r s e n i c i n these s t u d i e s was 4.1%. The response i n feed to gain r a t i o was 1.6%. The r e s u l t s shown i n Table 4 show the average responses from 5 t r i a l s i n v o l v i n g more than 2500 chickens f o r an 8-week feeding p e r i o d . This p e r i o d represents the time needed to b r i n g a

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

InArsenicalPesticides;Woolson,E.; ACSSymposiumSeries;AmericanChemicalSociety:Washington,DC,1975.

21

Turkeys

PoultrySwine

Swine

Poultry-

170g/ton(187 mg/kg)

45g/ton(50 mg/kg) 68g/ton(75 mg/kg)

90g/ton(100 mg/kg)

90g/ton(100 mg/kg)

p-ureidobenzenearsonic acid Turkeys 340g/ton(375 mg/kg) 1/ Source: (4) . 2] B r o i l e r s , l a y i n g hens and turkeys.

4-n i tropheny1arsonic acid

3- n i t r o - 4 hydroxyphenylarsonic acid

Arsanilic acid

~2T

Same as a r s a n i l i c a c i d

Same as a r s a n i l i c a c i d

Same as a r s a n i l i c a c i d Same as a r s a n i l i c a c i d

0.5 mg/kg f r e s h , uncooked muscle 2.0 mg/kg f r e s h , uncooked by-products 0.5 mg/kg f r e s h muscle and by-products other than kidney & l i v e r 2.0 mg/kg f r e s h , uncooked kidney & l i v e r

^, Maximum p e r m i s s i b l e l e v e l s of a r s e n i c a l s i n animal feeds and maximum D e r m i s s i b l e l e v e l s o f a r s e n i c i n animal t i s s u e . — Maximum Maximum Species feed l e v e l tissue arsenic l e v e l Compound

Table 2.

5.

CALVERT

Animal Feeds and

Wastes

73

chicken to market s i z e . In t h i s t e s t , the i n c r e a s e i n weight was not s i g n i f i c a n t , but feed conversion w i t h a r s e n i c supplement was s i g n i f i c a n t l y improved - 1.99 g of feed to produce 1 g of l i v e weight gain with the a r s e n i c a l compared w i t h 2.04 g of feed f o r each gram of g a i n with the c o n t r o l s . Table 3.

Treatment

Summary of t e s t s to show the e f f e c t of feeding 3-nitro-4-hydroxyphenylarsonic a c i d (0.005%) on the weight g a i n and feed e f f i c i e n c y of b r o i l e r c h i c k s during the f i r s t 4 weeks of l i f e . — Average Average feed Average feed conversion Average weight T r i a l s Bird conversio weight (No.) (No. weight)

3-Nitro 15 Nonmedicated controls 15 1/ Source: (9). Table 4.

1148

530

1148

510

4.1

1.70

1.6

1.73

Summary of t e s t s to show the e f f e c t of feeding 3 - n i t r o (0.005%) on the growth and feed e f f i c i e n c y , of b r o i l e r s during the f i r s t 8 weeks of l i f e . Average feed Average Trials conversion weight Birds (No..) (No.) (g feed/g weight) (g) 7

Treatment

3-Nitro 5 Nonmedicated controls 5 11 Source: ( 9 ) .

2568

1448

1.99

2568

1430

2.04

Results of an i n v e s t i g a t i o n by Hansen (10) on the response of growing swine to 3-nitro are shown i n Table 5. The a r s e n i c a l was f e d i n t h i s study f o r the f u l l growing p e r i o d and r e s u l t e d i n a s i g n i f i c a n t improvement i n both average d a i l y g a i n and feed conversion.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL PESTICIDES

74 Table 5.

E f f e c t of 3 - n i t r o on growth r a t e and feed conversion of growing sheep.— Average d a i l y g a i n from weaning Feed conversion to 90.9 kg (kg feed/kg weight) (kg)

3-nitro (40 mg/kg of feed) Nonmedicated c o n t r o l s 1/ Source: (10).

0.79 0.75

3.50 3.56

Reporting these r e s u l t s i s not intended as an endorsement f o r 3 - n i t r o as the a r s e n i c a l of choice i n animal feeding. S i m i l a r responses have been shown w i t h other a r s e n i c a l s such as a r s a n i l i c a c i d f o r chickens experiments reviewed f o a r s e n i c a l a d d i t i v e s were obtained i f supplementation d i d not exceed recommended l e v e l s . There were a few instances reported i n which no improvements i n growth and feed e f f i c e n c y were obtained from the a d d i t i o n of a r s e n i c a l s to swine and p o u l t r y d i e t s , but the high frequency of p o s i t i v e e f f e c t s from a r s e n i c a l s gives the producer that small edge that may w e l l be the d i f f e r e n c e between a p r o f i t and l o s s i n a modern swine and p o u l t r y feeding enterprise. A r s e n i c a l s are a l s o approved f o r feeding i n combination with other feed a d d i t i v e s such as c o c c i d i o s t a t s and a n t i b i o t i c s . There have been many experiments reported i n the l i t e r a t u r e t e s t i n g combinations of the a r s e n i c a l s with the wide v a r i e t y of a n t i b i o t i c s and c o c c i d i o s t a t s used i n p o u l t r y and swine d i e t s . Two reviews of these experiments (5,9) should be consulted f o r more detailed information. In many i n s t a n c e s , a combination of a r s e n i c a l and a n t i b i o t i c has improved growth that i s greater than that obtained w i t h e i t h e r of the a d d i t i v e s fed alone. There i s a t present no explanation as to why one a n t i b i o t i c w i l l respond one way when combined w i t h an a r s e n i c a l and another w i l l respond another way. Mechanism of. A c t i o n A number of t h e o r i e s have been proposed f o r the mechanism of a c t i o n of a r s e n i c a l s i n i n c r e a s i n g growth i n swine and p o u l t r y . Peoples (8) has suggested that the a r s e n i c a l may i n h i b i t those organisms that cause t h i c k e n i n g of the gut w a l l and therefore r e s u l t i n more e f f i c i e n t absorption of n u t r i e n t s . Another theory i s that these compounds a c t l i k e a n t i b i o t i c s and i n h i b i t harmful b a c t e r i a . However, s t u d i e s of the b a c t e r i o s t a t i c value of a r s e n i c a l s by F r o s t and Spruth (6) i n d i c a t e that with c e r t a i n b a c t e r i a , E s c h e r i c h i a c o l i and C l o s t r i d i u m p e r f r i n g e n s , f o r example, the a r s e n i c a l s are much l e s s e f f e c t i v e than conventional a n t i b i o t i c s . Another theory, proposed by Pope and Schaible (11),

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

5.

CALVERT

Animal Feeds and Wastes

75

suggests that a r s e n i c a l s may exert a sparing e f f e c t on p r o t e i n . In t h i s study, egg production i n hens f e d a 13% p r o t e i n d i e t was increased by the a d d i t i o n of a r s a n i l i c a c i d to the d i e t to a l e v e l comparable with the egg production i n hens f e d a 16.5% p r o t e i n r a t i o n . Russo e t a l . (12) a l s o found that a r s a n i l i c a c i d reduced u r i n a r y n i t r o g e n e x c r e t i o n i n swine, and they suggested that a r s e n i c a l s exert a sparing e f f e c t on p r o t e i n by reducing p r o t e i n catabolism. Thus, no one mechanism can l i k e l y e x p l a i n the a c t i o n of an a r s e n i c a l , and probably a combination of f a c t o r s produces the observed responses. Uptake and D e p l e t i o n of A r s e n i c from Tissue A r s e n i c a l s i n an animal' feed w i l l r e s u l t i a r s e n i residues i n t i s s u e s . Dat a r s a n i l i c a c i d a t 0.01 3-nitro-4-hydroxy phenylarsonic a c i d a t 0.005% r e s u l t s i n low l e v e l s of a r s e n i c i n l i v e r t i s s u e . Feeding 10 times the approved l e v e l s of e i t h e r of these a r s e n i c a l s d i d not r e s u l t i n 10 times the l e v e l of a r s e n i c i n the t i s s u e s . The data suggest that i n chicken l i v e r t i s s u e , there i s an upper l i m i t f o r a r s e n i c . These same authors a l s o presented evidence that a r s e n i c i n l i v e r and muscle of c h i c k s q u i c k l y reached a p l a t e a u l e v e l and d i d not i n c r e a s e f u r t h e r when a r s a n i l i c a c i d was f e d continuously a t 0.005% o f the r a t i o n f o r a 9-week p e r i o d . Table 6. Compound and

A r s e n i c found i n l i v e r s of chickens f e d v a r i o u s arsenicals.— A r s e n i c (As^O^) i n -

feed l e v e l

Arsanilic acid: 0.01% 0.1% 3-nitro-4-hydroxyphenylarsonic acid: 0.005% 0.05% Dodecylamine p-chlorphenylarsonate: 0.01% 1/ Source: ( 6 ) .

Feed —:

Fresh ppm

liver

45.4 455

1.2 6.4

18.7 187

2.4 7.5

23^3

2 ^

Evidence f o r the r a p i d i t y with which a r s e n i c i s taken up and e l i m i n a t e d from chicken t i s s u e s i s shown i n Table 7. These data by Baron (9) show that i n the kidney, l i v e r , muscle and s k i n of chicks f e d 0.005% 3 - n i t r o , there i s a l o w - l e v e l uptake of a r s e n i c that plateaus a f t e r 7 days of feeding and i s w e l l below tolerance l e v e l s a f t e r only 1 day of withdrawal o f the a r s e n i c a l .

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL PESTICIDES

76 Table 7. Days On Test On Med. Off Med.

Summation of a r s e n i c l e v e l s (3-nJtro, of the d i e t ) i n chicken t i s s u e s . — 1 1

-

Arsenic Kidney .93 Liver 1.31 Muscle .03 Skin .05 1/ Source: (9).

7 7

-

56 56

70 70

-

-

.005%

71

75

80

84

-1

-5

-10

-14

NonMed.

.22 .69 .03 .08

.10 .43 .01 .02

.09 .32 .02 .03

.08 .19 .02 .03

.05 .08 .02 .02

PPM

.76 2.43 .07 .11

.52 1.26 .05 .06

.64 1.26 .04 .05

Feeding a r s a n i l i c a c i a r s e n i c i n l i v e r , kidne muscle and blood. The method of feeding, and i n p a r t i c u l a r the water i n t a k e , may a l s o i n f l u e n c e the d e p o s i t i o n of t i s s u e a r s e n i c . Vorhies e t a l . (13) reported that a r s e n i c i n l i v e r increased from 1.8 ppm to 3.3 ppm when water intake i n swine was reduced. An e a r l i e r study by Bridges et a l . (14) a l s o showed t h i s e f f e c t . None of the a r s e n i c a l s have been approved by FDA f o r use i n feed f o r ruminant animals (beef c a t t l e , d a i r y cows or sheep). However, the c u r r e n t i n t e r e s t i n the use of animal wastes, p a r t i c u l a r l y d r i e d p o u l t r y excreta, as animal feed supplements has generated i n t e r e s t i n the a r s e n i c content of these wastes and i n the e f f e c t of a r s e n i c on the ruminant. Studies on the uptake of a r s e n i c from a r s e n i c a l s i n sheep have been conducted a t our l a b o r a t o r i e s at B e l t s v i l l e . In these i n v e s t i g a t i o n s , a r s e n i c , as a r s a n i l i c a c i d , has been fed to mature wethers at l e v e l s up to 273 mg/kg of d i e t f o r a p e r i o d of 28 days. The l e v e l s of a r s e n i c found i n various t i s s u e s i s shown i n Table 8. A l l t i s s u e s showed i n c r e a s i n g l e v e l s of a r s e n i c as the d i e t a r y a r s e n i c l e v e l s increased. Table 8. Arsenic fed (mg/kg of diet) 0.0 26.8 144.4 273.3

A r s e n i c l e v e l s i n t i s s u e s of wethers fed a r s a n i l i c a c i d f o r 28 days. Whole blood Liver Kidney Muscle mg/kg dry t i s s u e AsO, /ml by resting cells incubated with various concentrations of selenate, selenite, and sulfate t

Figure 7. Trimethylarsine production by a growing culture of Candida humicola in the presence of either 100 fig Na Se0 , 10 mg Na,SeO or 1.0 mg Na TeO,,/ml 2

h

3

2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

6. cox

91

Methylation of Arsenic

Figure 8. NaH AsOt 2

Selenite inhibition of trimethylarsine formation from by resting cells of Candida humicola. The concentrations shown are the levels of Na SeO . 2

a

% 5

I

I

250

Figure 9.

,

500 CONCENTRATION,

I

750

-

-L.

1000

>JG/ML

The effect of concentration of several compounds on the rate of dimethylselenide production by Candida humicola

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

92

ARSENICAL PESTICIDES

e i t h e r s e l e n i t e , arsenate or i n absence of both. The arsenate-grown c e l l s were then incubated i n presence of e i t h e r arsenate or s e l e n i t e and the time was measured f o r the formation of the appropriate gas. The same was done with the selenite-grown and the un-induced c e l l s . The l a g periods f o r trimethylarsine production from selenite-grown, arsenate-grown and un-induced c e l l s were measured and compared. As i s evident i n Figure 10, the arsenate-induced c e l l s produced trimethylarsine sooner than the s e l e n i t e induced c e l l s which i n turn were more rapid than the un-induced c e l l s . Likewise, the selenite-induced c e l l s produced dimethylselenide sooner than the arsenate-induced or the un-induced c e l l s . One might conclude that the methylatio separate enzymatic needed. As stated e a r l i e r , trimethylarsine production i s i n h i b i t e d by selenate and s e l e n i t e as well as phosphate however, the addition of these compounds did not only i n h i b i t trimethylarsine production but a c t u a l l y appeared to remove trimethylarsine from a growing c u l t u r e i n a closed system as indicated i n Figure 11. This was supported by demonstrating a l o s s of a known amount of authentic trimethylarsine placed i n a closed system with s e l e n i t e (17). A l o s s of the gas did not occur i n presence of phosphate or arsenate or i n absence of c e l l s (Figure 12). Previous work describing a chemical complex which can form between selenium metal (18) and trimethylarsine may explain the phenomemon since C. humicola suspensions containing s e l e n i t e produce an orange c o l l o i d a l material, i d e n t i f i e d as selenium metal (17), i n addition to dimethylselenide. No chemical evidence f o r such a trimethylarsine-selenium compound was found but i f formed, could account f o r the severe i n h i b i t i o n of the arsenic-methylating system. From an e c o l o g i c a l standpoint, studies are needed to determine i f v o l a t i l e forms can be assimilated and stored by higher animals. An arsenic analysis on a species of marine kelp found that t h i s plant was concentrating the metal one-thousand f o l d (19). In l i g h t of past evidence that methylated metals, namely mercury, can be bio-magnified to toxic l e v e l s by passing through natural food chains (20) studies are needed to determine i f t h i s phenomenon occurs with arsenic. To date one study has been made i n d i c a t i n g that some a r s e n i c a l s may not be as ominous as mercury. A model ecosystem containing four aquatic organisms with dimethylarsinic acid and dimethylarsine did not

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

cox

Methylation of Arsenic

Figure 10. The formation of trimethylarsine (top) and dimethylselenide (bottom) by cell suspensions of Candida humicola grown in the presence of 1.0 mg Na SeO /ml (A), 1.0 mg NaH AsO /ml (B) or neither (C) 2

i

2

h

}

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL PESTICIDES

94

no additions • IOOO jjg/ml KH P0 added 2

4

Figure 11. The effect of the addition of sodium selenate or potassium phosphate on trimethylarsine production by a growing culture of C . humicola

no additions 4CM 3020'

\

20 • 10'

0.5

1.0

1.5

no cells

1

Figure 12. Rate of disappearance of trimethylarsine incubated with and without cell suspensions of Candida humicola and 100 ^g of Na>SeO>, 1.0 mg of KH PO or NaH AsO,,/ml 2

2

h

20

4

3 o \

V

2 10-

^ 40a> 1 30 C (

As0 = 1000 pg/ml

0

05

1.0

1.5

o-o cells plus effector

Se0 =

pq=

100 >ig/ml

1000 jjg / ml

4

\

3Q |,

V

20 10

10 1.0

1.5 O HOURS

0.5

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

1.0

1.5

6. cox

Methylation of Arsenic

95

show s i g n i f i c a n t bio-magnification (21). In summary, evidence for the methylations of arsenic compounds by three mold species from sewage has been presented. The frequent use of arsenic compounds as pesticides provides a p o t e n t i a l hazard i f closed b i o l o g i c a l systems containing populations capable of methylating are exposed to a r s e n i c a l s . One of these three species, a yeast, has been shown to methylate selenium and probably t e l l u r i u m anions as well as arsenic compounds. The methylation mechanisms for selenium and arsenic i n t h i s organism appear to be p a r t i a l l y found i n a common pathway. Despite the widespread usage of arsenic compounds, l i t t l e i s known of the behavior of t h i s element i n natural ecosystems an hazard of arsenic poisoning is self-evident. L i t e r a t u r e Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

Challenger, F. Chem. Rev. (1945) 36:315-361. Gosio, B. Arch. I t a l . B i o l . (1893) 18:253-265. Gosio, B. Arch. I t a l . B i o l . (1901) 35:201-213. Challenger, F. " B i o l o g i c a l M e t h y l a t i o n , " Advances i n Enzymology, pp. 429-491, Interscience Publishers, New York, 1951. Challenger, F . , Higginbottom, C., and Ellis, L. J . Chem. Soc. (1933) 1933:95-101. Thom, C. and Raper, K. Science (1932) 76:548-550. Zussman, R., Vicher, E. and Lyon, I. J . B a c t e r i o l . (1961) 81:157. M e r r i l l , W. and French, D. W. Proc. Minn. Acad. S c i . (1964) 31:105-106. Epps, E. A. and Sturgis, M. B. Proc. S o i l S c i . Soc. Amer. (1939) 4:215-218. Woolson, E. A. and Kearney, P. C. Environ. S c i . Tech. (1973) 7:47-50. McBride, B. C. and Wolfe, R. S. Biochemistry (1971) 10:4312-4317. Wood, J . M . , Kennedy, F. S., and Rosen, C. G. Nature (London) (1968) 220:173-174. Cox, D. P. and Alexander, M. Bull. Environ. Contam. T o x i c o l . (1973) 9:84-88. Cox, D. P. and Alexander, M. Appl. M i c r o b i o l . (1973) 25:408-413. Da Costa, E. W. B. Appl. M i c r o b i o l . (1972) 23:4653. Fleming, R. W. and Alexander, M. Appl. M i c r o b i o l . (1973) 24:424-429.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

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17. Cox, D. P. and Alexander, M. Microbial Ecology (1974) 1 ( i n press). 18. Renshaw, R. R. and Holm, G. E . J. Amer. Chem. Soc. (1920) 42:1468-1471. 19. Gorgy, S., Rakestraw, N. W., and Fox, D. L. J. Marine Res. (1948) 7:22-32. 20. Katz, A. Crit. Rev. Environ. Centr. (1972) 2:517534. 21. Isensee, A. R., Kearney, P. C., Woolson, E. A., Jones, G. E . and Williams, V. P. Environ. S c i . Tech. (1973) 7:841-845.

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

7 Bioaccumulation of Arsenicals E. A. WOOLSON Pesticide Degradation Laboratory, Agricultural Research Service, U.S. Department of Agriculture, Beltsville, Md. 20705

Arsenic, as a natura accumulated by aquatic organisms for arsenic, as used i n this paper, i s defined as the ratio of arsenic concentration in the organism divided by the concentration of arsenic in water. An arsenic content of 2 μg/liter or 2 ppb, an approximate average for sea water, w i l l be assumed for data supplied by authors who did not measure the concentration of arsenic in sea water when analyzing arsenic in marine organisms. Salt water (marine) organisms accumulate much more arsenic than do most fresh water organisms. Furthermore, aquatic plants accumulate much more arsenic than do higher members in the aquatic food chains. In marine plants, BR values of 71,000 have been observed. A.

Arsenic in fresh waters

Arsenic concentrations measured in fresh water bodies are l i s t e d in Table 1. The concentrations reported in a survey of U. S. lakes and rivers ranged from (15) (10) (16)

a/ W SJ _V —f B.

Contains vanadium a l s o Less than 1% exceeded 10 yg/1 Watershed which r e c e i v e d lead arsenate Well dug through area c o n t a i n i n g grasshopper b a i t N a t u r a l l y contaminated a r t e s i a n w e l l water A r s e n i c i n marine waters

Concentrations o f a r s e n i c i n the marine environment g e n e r a l l y range from 0.15 t o 6 y g / l i t e r , with an average value o f ca. 2 yg/1 (Table 3). Areas near the r i v e r outflows tend t o have higher a r s e n i c l e v e l s than the oceans as a whole. The data o f Chapman (17) are 100-fold higher than those reported by other authors. No apparent reason f o r t h i s discrepancy e x i s t s . S c i e n t i s t s disagree as t o the o x i d a t i o n s t a t e o f a r s e n i c i n sea water. Many b e l i e v e that a r s e n i c e x i s t s i n sea water i n the +3 s t a t e ; others b e l i e v e that i t i s predominately i n the +5 s t a t e . Sugawara and Kanamori (18) showed that the +5 A s / t o t a l As r a t i o was c l o s e t o 0.8 i n ocean water. Diagrams o f vs pH f o r sea water i n d i c a t e that a r s e n i c would be i n the +5 s t a t e i n a l l o x i d i z i n g l a y e r s o f the ocean (19). Chemical reduction may take place at lower depths where o x i d a t i o n i s not great o r may be mediated by microorganisms. In any event, an e q u i l i b r i u m between arsenate and a r s e n i t e e x i s t s i n sea water. The same type o f e q u i l i b r i u m probably e x i s t s i n any s t r a t i f i e d lake (19) where p r e c i p i t a t i o n , o x i d a t i o n and r e d u c t i o n , and adsorption, reduction and methylation occur w i t h i n a s i n g l e lake. In the aerobic aqueous l a y e r , reduced forms o f a r s e n i c w i l l be o x i d i z e d to arsenate and both may c o p r e c i p i t a t e with f e r r i c hydroxide. Turbulence and convection t r a n s p o r t arsenate to the oxygen-depleted hypolimnion where i t may be reduced and form a r s e n i t e o r A s S . These reactions depend on s u l f u r concentration and the Eft. C o p r e c i p i t a t i o n , absorption, adsorption, and c r y s t a l 2

In Arsenical Pesticides; Woolson, E.; ACS Symposium Series; American Chemical Society: Washington, DC, 1975.

ARSENICAL PESTICIDES

100

Table 3.

A r s e n i c content o f marine waters

Source

Concentration (ug/As/1)

England England E n g l i s h Channel P a c i f i c coast N. W. P a c i f i c Ocean Indian Ocean S. W. Indian Ocean

106- 760 2> 2- 5 3- 6 0.15- •2.5 1.3- •2.2 1.4-5.0

Reference

(17) (20) (21, 22) ~ ( 6 r (6) (6) (6)

growth may cause arsenat reduction o f f e r r i c arsenat s o l u b i l i z a t i o n as a r s i n e s , s t a b i l i z a t i o n as i n s o l u b l e s u l f i d e s , or r e d u c t i o n t o a r s e n i c metal. M i c r o b i a l methylation and reduct i o n s o l u b i l i z e a r s e n i c , a l s o . Further, d i f f u s i o n through the sediments, or mixing by currents o r burrowing organisms, can cause the a r s e n i c to r e e n t e r the water phase. A r s e n i c i n the water phase i s adsorbed o r i n c o r p o r a t e d i n t o benthic organisms, algae, zooplankton and phytoplankton. T h i s a r s e n i c i s converted to organo-arsenical compounds as w e l l as water-soluble compounds w i t h i n these organisms (23, 24, 25). F i s h consume the algae o r microscopic organisms and f u r t h e r t r a n s form the a r s e n i c a l t o a more complex compound (26). Crustacea and f i l t e r - f e e d i n g s h e l l f i s h may absorb a r s e n i c from the water d i r e c t l y o r from microscopic organisms. C.

A r s e n i c i n f r e s h water organisms

In model ecosystem studies (Table 4 ) , c a t f i s h and Gambusia concentrated a r s e n i c from