SUBSTITUTE CHEMICAL PROGRAM
INITIAL SCIENTIFIC
REVIEW
CACODYLIC ACID
DECEMBER 1975
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF PESTICIDE PROGRAMS
CRITERIA AND EVALUATION DIVISION
WASHINGTON, D.C. 20460
t EPA-540/1-75-021
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This report has been compiled by the
Criteria and Evaluation Division,
Office of Pesticide Programs, EPA, in
conjunction with other sources listed
in the Preface. Mention of trade
names or commercial products does not
constitute endorsement or recommendation
for use.
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PREFACE
The Alternative (Substitute) Chemicals Program was initiated under Public
Law 93-135 of October 24, 1973, to "provide research and testing of substitute
chemicals." The legislative intent is to prevent using substitutes which in
essence are more deleterious to man and his environment than a "problem" pesti-
cide suspected of causing "unreasonable adverse effects to man or his environ-
ment." The major objective of the program is to determine the suitability of
potential substitute chemicals which now or in the future may act as replace-
ments for those uses (major or minor) of pesticides that have been cancelled,
suspended, or are in litigation or under internal review for potential unrea-
sonable adverse effects on man and his environment.
The substitute chemical is reviewed for suitability considering all appli-
cable scientific factors, such as chemistry, toxicology, pharmacology, environ-
mental fate and movement, use patterns and efficacy. EPA recognizes the fact
that even though a compound is registered, it still may not be a practical
substitute for a particular use or uses of a problem pesticide. The utilitarian
value of the "substitute" must be evaluated by reviewing its biological and
economic data. The reviews of substitute chemicals are carried out in two
phases. Phase 1 conducts these reviews based on data bases readily accessible
at the present time. An Initial Scientific Review is conducted to make a
judgment with respect to the "safety and efficacy" of the substitute chemical.
The Phase II Integrated Use Analysis examines the situation resulting from
possible regulatory action against a hazardous pesticide for each of its major
and critical uses. This Phase II analysis considers the suitable substitutes
reviewed during Phase I in conjunction with alternative management practices
to evaluate current and projected environmental, health, and economic impacts
of potential changes in pest management practices.
The report summarizes rather than interprets scientific data reviewed
during the course of the studies. Data is not correlated from different
sources. Opinions are not given on contradictory findings. This report con-
tains the Phase I Initial Scientific Review of Cacodylic Acid. Cacodylic acid
was identified as a registered substitute chemical for certain cancelled and
suspended uses of 2,4,5-T. The report covers all uses of cacodylic acid and
is intended to be adaptable to future needs. Should cacodylic acid be identi-
fied as a substitute for a problem pesticide other than 2,4,5-T, the review
can be updated and made readily available for use. The data contained in this
report was not intended to be complete in all areas. Data searches ended in
March, 1975.
The review was coordinated by a team of EPA scientists in the Criteria
and Evaluation Division of the Office of Pesticide Programs. The responsibil-
ity of the team leader was to provide guidance and direction and technically
review information retrieved during the course of the study. The following
EPA scientists were members of the review team: John Bowser (Team Leader);
Stewart Colten (Chemistry); Merry Lou Alexander (Chemistry); Clinton Fletcher
(Chemistry); Roger Gardner (Pharmacology and Toxicology); John Leitzke (Fate
iii
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and Significance in the Environment); Richard Petrie (Registered Uses);
Jeff Conopask, Ph.D. (Economics).
Data research, abstracting, and collection were primarily performed by
Midwest Research Institute (MRI), Kansas City, Missouri (EPA Contract #68-01-
2448) under the direction of Mr. Thomas L. Ferguson. RvR Consultants, Shawnee
Mission, Kansas, under a subcontract to MRI, assisted in data collection. The
following MRI scientists were principal contributors to the report:
James V. Dilley, Ph.D., David F. Hahlen, Alfred F. Meiners, Ph.D., William J.
Spangler, Ph.D., Frank E. Wells, Ph.D. Rosmarie von Rumker, Ph.D. (RvR Con-
sultants) also contributed to the report.
Draft copies of the report have been reviewed by the scientific staffs of
EPA's National Environmental Research Centers and their associated laboratories.
Comments and supplemental material provided by the following laboratories were
greatly appreciated and have been incorporated into this report: Gulf Breeze
Environmental Research Laboratory, Gulf Breeze, Florida and National Ecological
Research Laboratory, Corvallis, Oregon. The Ansul Company, a manufacturer of
cacodylic acid, reviewed the draft of this report and made certain comments and
additions.
iv
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GENERAL CONTENTS
Page
List of Figures vi
List of Tables vii
Part I. Summary 1
Part II. Initial Scientific Review 9
Subpart A. Chemistry 9
Subpart B. Pharmacology and Toxicology 45
Subpart C. Fate and Significance in the Environment 61
Subpart D. Production and Use 97
Part III. Efficacy and Performance Review 123
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FIGURES
No.
Patented Production Method for Cacodylic Acid.
Page
11
vi
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TABLES
No. Page
1 lonization Constants of Cacodylic Acid 24
2 pH at Which Metal Ions are Precipitated With Cacodylic Acid ... 26
3 Reduction Reactions of Cacodylic Acid 28
4 Reactions of Cacodylic Acid or Sodium Cacodylate 30
5 Arsenic in Total-Diet Samples 36
6 Daily Intake of Arsenic Residues 37
7 Acute Oral Toxicity to Rats 47
8 Dermal Toxicity (Mortality) of a Herbicide (77% Cacodylic Acid)
to Rabbits 50
9 Arsenic in Tissues of Chickens Fed Cacodylic Acid (30 ppm). ... 57
10 Cacodylic Acid (2.48 Lb Acid Equivalent/Gal) Herbicide
Specimen Label 102
11 Cacodylic Acid (3.1 Lb Acid Equivalent/Gal) Cotton Defoliant
Specimen Label 104
12 Cacodylic Acid (6.0 Lb Acid Equivalent/Gal) Tree-Killer
Specimen Label 106
13 Cacodylic Acid - Directions for Bark Beetle Control 108
14 Cacodylic Acid (1.25 Lb Acid Equivalent Plus MSMA 3.0 Lb/Gal)
Herbicide Specimen Label 109
15 Estimated Uses of Cacodylic Acid in the United States by Major
Functions and Areas of Use, 1973 114
16 Cacodylic Acid Uses in California by Major Crops and Other Uses,
1970 to 1973 116
vii
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TABLES (Continued)
No. Page
17 Use of Cacodylic Acid in California in 1972 by Crops and Other
Uses, Applications, Quantities, and Acres Treated 117
18 Use of Sodium Cacodylate in California in 1972 by Crops and Other
Uses, Applications, Quantities, and Acres Treated 118
19 Use of Cacodylic Acid in California in 1973 by Crops and Other
Uses, Applications, Quantities, and Acres Treated 119
20 Use of Sodium Cacodylate in California in 1973 by Crops and
Other Uses, Applications, Quantities, and Acres Treated 120
viii
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PART I. SUMMARY
CONTENTS
Page
Production and Use 2
Toxicity and Physiological Effects. .
*>"
Food Tolerances and Acceptable Intake
Environmental Effects
Efficacy and Performance
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1 lis section contains a summary of the "Initial Scientific Review"
conducted on cacodylic a'cid (dimethylarsinic acid) . The section summarizes
rather than interprets data reviewed.
Production and Use
Cacodylic acid, the common name for dimethylarsinic acid [(0113)2 As(0)OH],
is manufactured in the United States by The Ansul Company, Marinette, Wisconsin,
and Vineland Chemical Company, Inc., Vineland, New Jersey. Both the acid and
its monosodium salt are used for herbicidal purposes.
The sodium salt of the acid (sodium cacodylate or sodium dime thylarsinate)
is manufactured by a synthesis involving 5 reactions.
As203 + 6NaOH
Arsenic
Trioxide
Na~AsO + CH.C1
•j 3 3
3H0
Sodium
Arsenite
;> CH AsO(ONa) + NaCl
(1)
(2)
Methyl
Chloride
CH3AsO(ONa)2 +
CH3AsO + 2NaOH
DSMA
^> CH3As(ONa)2
Sodium
cacodylate
(3)
(4)
CH3As(ONa)2 -1- CH3Cl - — H?° ^v (CH3)2AsO(ONa) + NaCl (5)
Cacodylic acid is then made by acidification of the sodium salt:
(CH3)2AsO(ONa) + HCl
(CH3)2AsO(OH) + NaCl (6)
Cacodylic acid
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Cacodylic acid is a colorless, odorless, crystalline compound. It is
very soluble in water and can be used as a buffer. The cacodylate anion
[(CH3)2As02~] is very stable and easily interchanges cations to form a wide
variety of other salts. Cacodylic acid is very stable toward chemical
oxidation. Cacodylic acid reacts with thiols but the reaction products are
unknown. Cacodylic acid is amphoteric and reacts as a base with stronger
acids.
The technical product is 65% aqueous cacodylic acid, and contains salts,
including sodium chloride. Water is the principal solvent in formulations,
which usually have sodium cacodylate as the principal active ingredient and
cacodylic acid as the minor active ingredient. Generally, the formulations
are 20 to 30% strength (cacodylic acid equivalent), but the tree-killer formu-
lation is 50%, and contains only the acid form. At least two formulations are
available that contain cacodylic acid in combination with monosodium
methanearsonate (MSMA) as active ingredients. No dry powder or granular
formulation of cacodylic acid are available.
Cacodylic acid (and its sodium salt) is a contact herbicide, capable of
defoliating or dessicating a wide variety of plants. It is currently regis-
tered in the United States for general weed control in noncrop areas, for weed
control by directed application* in nonbearing citrus orchards, for lawn
renovation, for defoliation of cotton, and for crown kill of undesired trees.
Cacodylic acid is also used by professional foresters and entomologists
only for the control of bark beetles.
The estimated domestic use of cacodylic acid in 1973 was 1,300,000 to
1,700,000 Ib acid equivalent. About 50% of that quantity was used for nonse-
lective weed control, 40% for cotton defoliation, about 1% for forest management,
with the remainder being used for all other" purposes, including lawn usage.
Toxicity and Physiological Effects
Specific information on acute, subacute, or chronic toxicity of cacodylic
acid to man by oral, dermal, or respiratory routes was not found. A potential
occupational hazard for forestry workers using cacodylic acid in tree-thinning
operations has been suggested, although toxic effects in these workers were not
evident. Exposures were monitored by increases in urinary excretion of arsenic.
In tests on rats, the acute oral toxicity (LDso) reported for cacodylic
acid herbicide formulations ranged from 0.7 to 2.6 g/kg of body weight. Signifi-
cant sex differences were not indicated (LDso °f 1-4 g/kg for males versus 1.28
g/kg for females). When weanling rats were fed at dietary levels equal to 10,
20, and 40% of the estimated oral LDso (0.70 g/kg), little effect was noted on
various tissues examined except for reduced activity of spermatogonia cells at
the 40% treatment level.
"Directed application" means that this herbicide is not allowed to contact
the leaves, stems, or bark of the crop in which weeds are to be controlled.
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Subacute toxicity tests (90 days) indicated that dietary cacodylic acid
was nontoxic at 30 ppm to dogs and at 100 ppm to rats.
Rabbits treated by dermal application of cacodylic acid (77%) exhibited
mortality at lower dose levels when the skin was abraded than when it was
intact. With abraded skin a dose of 1.0 g/kg was lethal for the rabbit, but
with intact skin death did not occur until the dose reached 2.5 g/kg.
Skin and eye irritation tests with rabbits appeared to indicate that
cacodylic acid formulations could be considered essentially nonirritating to
both skin and eyes.
Subacute toxicity was the only area in which reports were found for domestic
animals. Cattle given cacodylic acid (by capsule) at 25 mg/kg for 10 days
exhibited no ill effects. When cacodylic acid was given by drench at 50 mg/kg,
toxic signs appeared after the first dose and death after the seventh. Sheep
treated for 10 days at 50 mg/kg (capsule) exhibited signs of toxicity after the
second dose but did not die after 10 doses. A weight loss of 22% resulted from
the treatment.
Chickens were fed for 10 weeks at dietary levels up to 30 ppm arsenic
(cacodylic acid) without any apparent toxic effects. Eggs from the hens fed
at the 30-ppm level contained 0.22 ppm arsenic after 1 month and 0.23 ppm after
2 months feeding.
In other studies chickens fed 10 daily doses of 100 mg/kg of body weight
exhibited no toxic signs. However, chickens treated at 500 mg/kg had only a
13% weight gain compared to a 53% gain for controls.
Metabolic studies specifically designed to determine mammalian absorption,
distribution, excretion, and residual potential of cacodylic acid are lacking.
One study on absorption was reported on the rat. The mechanism by which caco-
dylic acid was absorbed appeared to be simple diffusion; the absorption half-
time was calculated to be 201 min. In the cow, cacodylic acid was excreted
primarily in the urine and residues were not found in milk. '
Nonavailability of tissue-bound arsenic was shown by studies in which
animal products that contained arsenic were fed to rats, chickens, and man. It
appears that trivalent arsenite is oxidized to pentavalent arsenate in mammals.
Most of the organic arsenicals (the pentavalents) are excreted essentially
unchanged so that their toxic effect is unlikely to be related to conversion to
an inorganic arsenic compound.
Rapid clearing of tissue residues of arsenic after animals are removed
from feeds containing various arsenicals was demonstrated for cattle, chickens,
and swine. Only studies on the mutagenic effects in bacteria have been reported
for cacodylic acid; in this system, a mutagenic potential was not found. Repro-
ductive and teratogenic effects have not been reported for cacodylic acid in any
species. EPA laboratories at Research Triangle Park, North Carolina, are currently
studying the teratogenic effects of cacodylic acid on rats and mice.
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Dietary tests to determine the tumorigenic effect of cacodylic acid in
mice were conducted for 18 months; the treatment did not-cause any increase in
hepatomas, pulmonary tumors, lymphomas, or in total numbers of mice with
tumors over the values found for untreated control animals.
Food Tolerances and Acceptable Intake
Analytical methods which distinguish residues of specific arsenical
compounds in plant materials are not presently being used in the analysis of
food and feed. Rather, samples are analyzed for total arsenic (as As203).
Results, therefore, include naturally occurring arsenic levels in addition to
pesticide residues.
There are currently tolerances for cacodylic acid (calculated as AS203) of
0.7 ppm in cattle (meat, fat, and meat by-products except kidney and liver),
1.4 ppm in beef kidney and liver, and 2.8 ppm in cottonseed.
Investigators who have monitored the levels of arsenic in food and feed for
a 6-yr period have concluded that the dietary intake of arsenic from pesticide
residues is not significant.
An acceptable daily intake (ADI) has not been established for cacodylic
acid.
Environmental Effects
The data available on the toxicity of cacodylic acid to fish is limited
to acute toxicity. The 96-hr TLm of a 23.4% cacodylic acid formulation for
bluegill (Lepomis macrochirus) is reported to be 80 ppm. The 96-hr I^g for
a second formulation (percent cacodylic acid not stated) was reported to be
16 ppm for bluegill.
One field study was made of the effect on fish populations of cacodylic
acid in runoff. Only one of the 20 species monitored was found to decrease
significantly in population between pre- and post-treatment counts. The random
effects on the species and the low levels of arsenic in the runoff water (<.0.05
ppm), however, led the investigators to conclude that variations in populations
were not due to the cacodylic acid. During this study, the population levels
of several benthic organisms were also monitored, including crayfish (Orconectes
species), dragonfly naiad (Gomphus species), freshwater snail (Neritian species),
and an unidentified immature freshwater clam. Observations were also made to
detect possible morphological effects on eelgrass (Vallisneria americana). None
of these organisms exhibited any gross changes in population levels; all remained
abundant throughout the study period.
No effects were noted when pink shrimp (Penaeus duorarum) and longnose
killifish (Fundulus similis) were exposed to 40.0 ppm active ingredient (AI) of
cacodylic acid for 48 hr or in Eastern oyster (Crassostrea virginica) exposed to
1.0 ppm AI for 96 hr.
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Information from controlled studies concerning the effects of cacodylic
acid on wildlife is limited to studies of its oral toxicity to. 3 avian species
and 1 species of deer. The 8-day dietary LC5Q for mallard ducklings (Anas
platyrhynchos) is greater than 5,000 ppm. A material containing 29% sodium
cacodylate and 5% cacodylic acid was also calculated to have an 8-day dietary
LC5Q for bobwhite quail (Colinus virginianus) of greater than 5,000 ppm.
The LDcjQ of a formulation containing 54.3% cacodylic acid for mallard hens
is greater than 2,000 mg/kg and equal to or greater than 2,000 mg/kg for the.
chukar partridge (Alectoris graeca).
Studies have been made of the fate and environmental impact of organic
arsenical herbicides, including cacodylic acid, used in the forest environments
of the Pacific Northwest. More than 400 determinations were made of arsenic
residues in specific tissues and whole body samples from animals trapped at
various intervals after use of the arsenicals. About 50% of the animals cap-
tured between 2 and 30 days following treatment contained arsenic residues be-
tween 0.5 and 9.8 ppm. One animal collected 1 day after treatment contained
arsenic residues ranging from 17 to 30 ppm in various body parts. Few animals
collected more than 30 days after treatment contained detectable arsenic resi-
dues.
Conflicting results have been reported from studies of the toxic effect of
cacodylic acid to honeybees (Apis mellifera). Cacodylic aci
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volatile organoarsenical within 24 weeks and was lost from the soil system;
under aerobic conditions, 35% was converted to volatile organoarsenical com-
pounds .
The effect of repeated applications of cacodylic acid on arsenic residues
in the soil has been evaluated. After 6 annual applications at rates of 2.5
and 7.5 Ib of acid equivalent per acre, statistically significant buildup of
arsenic was detected in the top 6 in of soil for both rates (2.4 to 4.5 ppm
above the average background of 11 ppm). Arsenic concentrations in the 6- to
12-in layer were increased by the higher rate, while the 12- to 18-in layer
was not affected by either rate.
Available data indicates that herbicidally effective concentrations of
cacodylic acid "disappear" rather rapidly from field soils after application.
Microbial activity appears to some extent to contribute to their degradation.
Several different chemical reactions also seem to be involved. A number of
crops have been tested in order to evaluate the effect of cacodylic acid on
their respective arsenic content. Snap beans, potatoes, sweet potatoes, carrots,
Chinese cabbage, field corn, and soybeans were planted in plots which had been
treated with 5 Ib of cacodylic acid per acre. No significant uptake of arsenic
was detected in the edible parts of the crops. In a companion study, no uptake
of arsenic was detected in alfalfa or ryegrass from plots that had been similarly
treated.
Regarding the effects of cacodylic acid in water, one study was reported
in which 5 Ib of cacodylic acid per acre were applied to irrigation canals.
The highest arsenic concentration detected in the water was 0.86 ppm; this level
dropped to less than 0.1 ppm in less than 2 hr.
There were no reports found on the presence, fate, persistence, or signi-
ficance of cacodylic acid in the air. However, some investigators have suggested
that cacodylic acid (and other organic arsenicals) may be reduced and methylated
to form volatile compounds which escape from treated areas into the air.
Studies have been made in a model ecosystem in which mosquitofish (Gambusia
affinis), Daphnia magna, Physa snails, and algae (Oedpgonium cardiacum) were
exposed for 3, 29, 32, and 32 days, respectively, to -^C-labeled cacodylic acid
at a concentration of 11.5 ppb. In this system, algae were found to be the
primary sink in which cacodylic acid residues accumulated. Algae and daphnids
bioaccumulated more cacodylic acid residues than did the two higher food chain
organisms, snails and fish, indicating that cacodylic acid did not biomagnify
between food chain organisms.
Other tests have shown that fish and snails accumulated 2 to 10 times more
cacodylic acid from solution than from consuming cacodylic-treated Daphnia or
algae.
In still another aquatic ecosystem, bottom-feeding organisms (catfish,
Ictalurus punctatus; and crayfish, Procambarus clarki), and duckweed (Lemna
minor) were exposed to 3 soils containing 14c-labeled cacodylic acid. Based
on the results from this study, the investigators concluded that cacodylic
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acid does not bioaccumulate in the aquatic organisms studied. However, cray-
fish did accumulate arsenic, particularly in their soft tissue, in the 3
different tests.
The data regarding the behavior of cacodylic acid in soil and water, al-
though limited, indicates that movement of cacodylic acid from treated land
to water by leaching or surface runoff appears to be minimal.
Efficacy and Performance
Cacodylic acid is a nonselective herbicide used for control of weeds and
grasses along ditch banks and rights-of-way, for cotton defoliation, for con-
trol of hardwood trees, and for suppression of bark beetles.
Cacodylic acid has shown up to 100% crown kill when applied to quaking
aspen, red maple, paper birch, jack pine, and oak. Poor crown kill was
observed on hickory and blackgum. Although it gives good crown kill, most
trees survived when measured over a 2-year period.
Use of the Hypo-Hatchetfiy to apply cacodylic acid does not appear to
increase the rate of tree kill, but it has been shown to be 2 to 3 times as
efficient as other application methods.
Control of the bark beetle in spruce, ponderosa pines, and loblolly pines
can be as high as 99% when these trees are treated with cacodylic acid. The.
use of attractants to lure the insect to the treated tree has been successful
in increasing the number of insects killed. However, some doubts exist if
cacodylic acid is translocated in the southern pine to provide control of the
southern pine beetle.
Although cotton defoliation is a significant use of cacodylic acid, a
search of the literature did not produce any information on its efficacy.
Additional contacts at selected extension agencies also revealed a lack of
this type of information.
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PART II. INITIAL SCIENTIFIC REVIEW
SUSPART A. CHEMISTRY
CONTENTS
Page
Synthesis and Production Technology 10
Physical Properties 16
Analytical Methods 17
Information Sources 18
Multi-Residue Methods 18
Residue Analysis - . . 18
Formulation Analysis 21
Composition and Formulation 22
Chemical Properties, Reactions, and Decomposition Processes 23
Acidic and Chemical Properties 23
Oxidation and Reduction Reactions. 27
Reactions of Cacodylic Acid and Sodium Cacodylate to Form Other
'Salts 27
Other Reactions 27
Occurences of Residues in Food and Feed Commodities 33
Acceptable Daily Intake 34
Tolerances 35
References 38
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This section reviews available data on cacodylic acid's chemistry and
presence in foods. Eight subject areas have been examined: Synthesis and
Production Technology; Physical Properties of Cacodylic Acid; Composition and
Formulation; Analytical Methods; Chemical Properties; Occurrence of Residues
in Food and Feed Commodities; Acceptable Daily Intake; and Tolerances. The
section summarizes rather than interprets scientific data reviewed.
Synthesis and Production Technology
Cacodylic acid, the common name for dimethylarsinic acid [(CH3)2 As(0)OH],
is used in the control of weeds, cotton defoliation, forest management, and
lawn restoration.
It was introduced as a herbicide in 1958 by The Ansul Company, Marinette,
Wisconsin. However, the chemical has been known for over 130 years, Bunsen
(1843) was one of the earliest researchers to work with the compound. The
only known present domestic manufacturers of this compound are The Ansul
Company and Vineland Chemical Company, Inc., Vineland, New Jersey. However,
one patent on a manufacturing process was issued to 0. M. Scott and Sons
Company (Schanhals 1967).
A process flowsheet for cacodylic acid is presented in Figure 1. Cacodylic
acid is manufactured from disodium methanearsonate (DSMA) , CH3AsO (ONa) 2 > which
is also a commercial herbicide. The following equations illustrate that DSMA
is initially synthesized in a two-step reaction sequence:
As203 + 6NaOH > 2Na3As03 + 3H20 (1)
Arsenic Sodium
Trioxide Arsenite
Na3As03 + CH3C1 > CH3AsO(ONa)2 + NaCl (2)
Methyl DSMA
Chloride
Reaction equations for the subsequent manufacture of cacodylic
acid are as follows:
H20
CH3AsO(ONa)2 + S02 > CH3AsO + Na2S04 (3)
DSMA Sulfur Methylarsine
dioxide oxide
10
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As2O3 — **
H2O — *•
NaOH — >
cH3cn *
S02
N2> — *>
NaOH
CH3CIJ
Sodium
Arsenite
Unit
^ Eyases l5U2,iN2f<->2,t~n3V.i;
1 1
Sodi urn
Dimethyl
Arsinate Unit
( Pressure
Reactor )
U/-I Kl_^/~l
1
1 1
c tfi- (CH3)2AsO^ONaJ .....
Settling : .°'r ' Acidification Cooling
and v ^ and _ and
Sol
Reirw
i
Centr
o
Filt
ids j , ^Oxidation ^ Settlinq
.Nda,Na2S04 1 NaU.Naj
and Cn3AsO(ONa)2
. Centrifuge
- * or
ifuge Filter
er
1
H2O CH3OH
t 1
Technical
• Evaporator "^ Cacodylic
Acid
jS04
1e A ii i c •• 1 1
Solid Wastes
Figure 1. Patented production method for cacodylic acid.
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CH3AsO + 2NaOH > CH3As(ONa)2 + H20 (4)
Sodium Disodium
hydroxide methylarsonite
H2°
CH3As(ONa)2 + CH3C1 ^ (CH3)2AsO(ONa) + NaCl (5)
Methyl Sodium
chloride dimethylarsinate
H20
(CH3)2AsO(ONa) + HC1 > (CH3)2AsO(OH) + KaCl (6)
Cacodylic acid
Reaction (3) is very rapid at temperatures below 200°F, and at any
pressure. The reaction is complete in 5 to 15 min (Schanhals 1967).
Reaction (4) is the most critical step in yield efficiency. After
Reaction (3), the excess S02 is purged using a gas which is inert to the
methylarsine oxide. Nitrogen is preferred, but C02 or other inert gases may
be used. Two alternates are: use of the alkylating agent as the purge gas or
evacuation of the oxygen, followed by purging. The evacuation-purge cycle is
repeated several times (Moyerman and Ehman 1965).
A low oxygen content is required in order to prevent the following oxida-
tion reaction from occurring (Schanhals 1967):
2CH3AsO + 02 + 2H20 ——> 2CH3AsO(OH)2
Methylarsonic
acid
Moyerman and Ehman (1965) specify the following conditions related
to oxygen concentration.
Oxygen content of Ratio of oxygen
atmosphere on reaction to CH3AsO
mixture (moles/liter) (moles/mole)
"Should be" less than 300 x 10"5 200 x 10'5
"Preferably" less than 160 x 10'5 125 x 10'5
"Especially good results" 70 x 10'5 55 x 10~5
when less than
12
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A second important condition for Reaction (4) is the pH. Moyerman and
Ehman (1965) report that, above a pH of 10.5, the following side reactions
occur, but may be avoided by excluding air.
3CH3AsO > As203 + (CH3)3As (7)
Trimethyl-
ars ine
4CH3AsO > [(CH3)2As]20 + As203 (8)
Cacodyl
oxide
Noller (1957) reports the following reactions:
[(CH3)2As]2 0 + 2 NaOH -*> H20 + 2 (CH3)2As 0 Na (9)
(CH3)2AsONa + CH3CL -> (CH3)3 As 0 + NaCL (10)
Trimethyl arsine
The formation of trimethylarsine is undesirable because of the resultant
decrease in yield. In addition, (CH3)3As is flammable, toxic and has a
disagreeable odor.
The specific recommendations of Moyerman and Ehman (1965) in regard to pH
are quoted directly from the patent as follows.
In carrying out the reaction, it is desirable that the
aqueous solution of the arsenoso substituted organic compound
(for example, methyl arsineoxide) be maintained at a pH less
than about 10 and preferably less than about 7, until the
oxygen content has been reduced to the desired level. Follow-
ing removal of the oxygen, the pH of the reaction mixture is
adjusted to the alkaline range, as by the addition of an
alkalimetal hydroxide. Preferably, the pH may be regulated
following oxygen removal by adding an alkali metal hydroxide
such as sodium, potassium or lithium hydroxide. Enough of
the alkali metal hydroxide is added to insure a large stoi-
chiometric excess, based upon the arsenoso substituted hydro-
carbon. Because of the large excess of alkali metal hydroxide
employed, the pH of the reaction mixture at the start of
alkylation will ordinarily be about 14. As the alkylation
reaction progresses, the pH gradually falls until the akyla-
tion is complete, at which time the pH is between about 5.5
and 6.5.
13
-------
In Reaction (5) the alkylating agent is usually CH3C1, but Ch3Br, 013!,
or (0113)2804 may be used (Moyerman and Ehman 1965). According to Schanhals
(196."), Reaction (5) is carried out by bringing the disodium methylarsonite
up to reaction temperature (75 to 200 °F) and treating the reaction mixture
with superheated CH3C1. Pressures may range from 40 to 175 psig. The best
temperature and pressure for the reaction are 175°F and 150 psig. The above
3 process reactions are all carried out in the same pressure reactor.
Reaction (5) is the production of the sodium salt of cacodylic acid.
Whether the salt form is to be used directly or converted to the acid, the
following steps are taken, as quoted from Schanhals (1967) :
The products . . . are present in a slurry which is
pumped out of the reactor. The solids are then removed by
conventional methods, preferably by pumping the reaction
products to a settling tank and cooling them. Most of the
Na2S(>4, some NaCl, arid some reaction by-products have pre-
cipitated in the pressure reactor. Residual amounts remain-
ing in solution precipitate out in the settling tank as the
solution cools.- The precipitated solids may then be de-
watered using a filter, centrifuge, or similar unit. The
mother liquor and the liquid phase remaining in the settling
tank are pumped to a second reactor. The liquid phase pumped
into that reactor is a solution of the sodium salt of dimethyl-
arsinic acid (sodium dime thy larsinate) .
According to Ottinger et al. (1973), there is no liquid effluent from this
process because all the liquid streams are recycled for reuse. A number of
multiple effect evaporators are employed in the solution recycling systems.
The process does, however, create a solid waste which is a mixture of sodium
chloride and sodium sulfate containing 1 to 1-1/2% cacodylate contaminants.
If the sodium salt is to be converted into cacodylic acid, Reaction (6) is
a simple addition of hydrochloric acid, done at ambient condition. Sulfuric,
nitric, or phosphoric acids could also be used (Schanhals 1967). Acidification
is not carried to completion.
Schanhals (1967) recommended an additional oxidation step to reduce the
toxicity and odor of the reaction mass. This may be performed on the sodium
salt or cacodylic acid itself. Possible oxidation agents are sodium hypochlor-
ite, hypochlorous acid, hydrogen peroxide, and others. The preferred oxidizing
agent is said to be sodium hypochlorite. Typical reactions which occur in this
oxidation step are as follows:
CH3AsO + H20 + NaOCl - 5> CH3AsO(OH)2 + NaCl (11)
As(ONa)3 + NaOCl - > AsO(ONa)3 + NaCl (12)
As (OH) + NaOCl - > AsO(OH) + NaCl (13)
As0 + NaOCl - > As0 + 2NaCl (14)
14
-------
(CH3)3As + [0] -+ (CH3)3AsO
[(CH3)2As]2 0 + 02 + H20 -» 2(CH3)2 As (0) OH
Ambient conditions are also used for this reaction.
(15)*, **
(16)** See also below
Schanhals (1967) described the manufacturing process as follows:
The arsinic acid or salt solution is pumped to an evapora-
tor or similar device and water . . . removed, precipitating
additional quantities of NaCl and Na2S04- The solids may be
removed from the solution by any conventional means. In the
preferred process, the hot concentrate is first cooled in a
settling tank and the insoluble impurities then removed. Ad-
ditional solution is then removed from the solids by conven-
tional devices such as filters or centrifuges and the mother
liquor added to the solution removed in the settling tank.
An alternate method of production was described by Melnikov (1971) :
dry
4CH3COOK
dist.
[(CH3)2As]20
(17)
Potassium
acetate
(anhydrous )
[(CH3)2As]20
Cacodyl
oxide
2(CH3)2As(0)OH
Cacodylic acid
However, Schanhals (1967) concluded that the method is uneconomical commercially
because of expensive starting materials and a relatively low conversion.
Noller (1957, p. 900) gives:
(CH3As + 02 -> (CH3)AsO:
(15a)
CRC Handbook of Chemistry and Physics (1969) shows:
2C10~ + 2H20 + 4e - 2C1~ + 40H~ 0.90 Volt
40H~ =£• 4e + 02 + 2H20 -.401 Volt, so that overall
2C10- ^= 02 + 2C1- .499 Volt (15b)
At 25° the equilibrium constant of this reaction is log"1 (.499 (4) -r .059)
= log~l(E°nF/RT) or about 10^4. Thus, it may be safely assumed that the
hypochlorite will be releasing substantial free oxygen for reaction (15a) .
** The trimethylarsine and cacodyl oxide for reactions (15) and (17) would be
present, for example, if the by product reactions (7) and (8) could not
be prevented.
15
-------
Laboratory Preparation - Conversion of methylarsine oxide to cacodylic acid,
as reported by Moyerman and Ehman (1965), is 98%.
Physical Properties
Chemical name: Dime thy larsinic acid
Hydroxydimethylarsine oxide
Common name: Cacodylic acid
Derivation of name; Cacodylic acid has been known for many years. The
prefix cac- or caco- comes from the Greek word kakos, meaning bad. The Greek
word kakodes meant ill- smelling. Cacodyl refers to an arsenical radical As (013) 2
whose compounds are noted for their vile smells and poisonous properties, or to
the compound with 2 radicals joined,
Cacodylic acid, (CH3)2As(0) OH, contains the cacodyl radical with a double
bonded oxygen and a hydroxyl group attached to the arsenic atom. The acid
itself is odorless, despite the name.
Other nangs;. Phytar® 138, Chexmate®, Rad-E-Cate®, Silvisar® 510.
Pesticide class: Herbicide, arsenical.
Empirical formula: Cacodylic acid Sodium cacodylate
Structural formula: CH-> 0 CHo 0
- 3^ 4, . J\ 4*
As As
Molecular weight: 137.99 159.98
Analysis Percent Percent
C 17.41 15.01
H 5.11 3.78
As 54.29 46.83
0 23.19 20.00
Na 14.37
Structural data: Cacodylic acid crystals are triclinic, with
unit-cell dimensions of a = 6.53 nm, b = 6,82 nm, c = 6.61 nm, a = 77°30',
0 = 98045', Y = 55°9' (Trotter and Zobel 1965).
16
-------
Smith et al. (1970b) listed different unit-cell dimensions; a - 8.34 nm,
b = 6.82 nm, c = 10.16 nm, a = 59.5°, $ = 89.3°, y = 106.0°.
The configuration is tetrahedral about the arsenic atom; the bond angles
are in the range of 106 to 115° (Trotter and Zobel 1965).
Bond Bond length (nm)
As - C 1.91 ± 0.04
As - O(both) 1.62 ± 0.03
0-H' • -0(hydrogen bond) 2.57
Physical state; Colorless, odorless crystals. Hygroscopic.
Technical product is 65% pure, containing NaCl as an impurity (Martin
1971). The sodium salt is deliquescent.
Density: 1.95 g/ml (Smith et al. 1970b). From unit-cell volume, not
actual measurement.
Melting point (°C): 195-196 (crystals from alcohol ether)
(Merck 1968)
192-198 (Martin 1971)
200 (Weed Society of America 1970)
200 (Frear 1969)
Enthalpy of fusion; 4.96 kcal/mole (Smith et al. 1970a).
Solubility; Very soluble in water, 83 g acid to 100 g water at 22°C.
Solubility in ethyl alcohol, 28.5 g/100 ml at 15°C (Bailey and White 1965),-
20.6 g/100 ml at 20°C (Herbicide Handbook 1970). Soluble in acetic acid, but
not in ethyl ether.
Sodium salt; 82 g of salt is soluble in 100 g of water.
pH; 7.7 to 8.0 (4% solution of sodium cacodylate). (Masucci and Moffat
1923.)
3.1 [1 molar solution of acid, calculated from pKa given by Jacobson et al.
1972].
Corrosivity; Aqueous solution is mildly corrosive.
Analytical Methods
This subsection reviews analytical methods for cacodylic acid. The review
describes (a) multi-residue methods, (b) residue analyses, and (c) formulation
analyses. Information on the sensitivity and selectivity of the methods is also
presented.
17
-------
Information Sources - The primary information sources for the analytical
methods are as follows: (1) The Pesticide Analytical Manual (PAM 1967),
published by the Food and Drug Administration (FDA), is designed to bring
together procedures and methods used by the FDA laboratories to examine food
samples for the presence of pesticide residues. PAM is published in 2
volumes. Volume I contains procedures for multi-residue methods (for samples
of unknown history which may contain more than one pesticide). Volume II
contains analytical methods used for specific pesticide residues and for
specific foods. (2) Official Methods of Analysis of the Association of Official
Analytical Chemists (AOAC 1970) is a methods manual published about every 5 yr.
The reliability of the methods must be demonstrated by a published study show-
ing the reproducibility of the method by professional analysts. Methods and
collaborative studies are published in the Journal of the Association of Official
Analytical Chemists.
Multi-Residue Methods - There are no multi-residue methods which specifically
detect cacodylic acid. The residue analyses performed by FDA do not detect
cacodylic acid as an individual chemical; all forms of arsenic are converted to
arsenic trioxide (AS203).
Residue Analysis - The Diamond Shamrock Chemical Company (1970) explains the
difficulty in detecting residues of arsenical pesticides as follows:
Analytical methods which can distinguish residues of specific
arsenical compounds in plant materials are not available. Gas
chromatography and thin-layer chromatography methods do not
have sufficient sensitivity to quantitatively analyze methane-
arsonate herbicides.
There have been some recent developments which may lead to practical,
specific methods for the determination of cacodylic acid residues. These are
discussed below.
Sachs et al. (1971) developed a paper chromatographic separation method
for cacodylic acid and other arsenicals. Four solvent elution systems were
employed. Aqueous extraction of plant tissues removed essentially all of the
arsenieals applied. The paper chromatographic procedures were followed by
colorimetric determinations of the separated arsenicals. The silver diethyl-
dithiocarbamate colorimetric method was useful for detecting as little as 0.6
to 20 yg of arsenic (the color is caused by the formation of an arsine-silver
diethyldithiocarbamate complex).
Soderquist et al. (1974) have reported a procedure whereby cacodylic acid
and its salts can be determined rapidly with a detectability limit below 0.05
ppm in water and 0.5 ppm in soil. The method, which excludes other arsenicals,
is based upon conversion of cacodylic acid to iododimethylarsine with hydriodic
acid:
HI
18
-------
Added
(ppm)
0.15
0.15
0
1.5
0
Found
(ppm)£/
0.137 (± 0.012)^
0.150 (± 0.004)
< 0.050
1.22 (± 0.11)
< 0.50
Recovery
(%)— '
92.3 (+ 7.4)
100 (± 2.6)
0
81.3 (±5.1)
0
The iododimethylarsine is determined by means of electron-capture
gas chroraatography. Recoveries of cacodylic acid from water and soil
are as follows.
Cacodylic acid
Added Fo
Sample
Distilled water
Rice water
Rice water (blank)
Dinuba soil
Dinuba soil (blank)
a/ Standard deviation from 3 samples.
Interferences in the water analyses were not serious and, according to
the authors, the detectability limit of 0.05 ppm could be lowered
further by using a larger water sample. Attempts failed to lower the
detectability limit in soil (about 0.5 ppm) by prior extraction of the
cacodylic acid with methanol or aqueous methanol probably due to binding
with soil particles.
Braman and Foreback (1973) developed a method for analyzing various
forms of methylated arsenic acids in the environment at low concentra-
tion. This method depends upon reduction of cacodylic acid to dimethyl-
arsine, (CHoJoAsH, by sodium borohydride at pH 1 to 2. This volatile
arsine is then scrubbed out with helium gas and frozen in a liquid
nitrogen trap. The arsine gas is then volatilized from the trap and
a recording is made of the intensity of arsenic emission lines (234.9
run or 228.8 nm) produced by an electrical discharge in the carrier
gas. The limit of detection is very low, 0.5 ng. Braman and Foreback1 s
method is also applicable to arsenite ion, arsenate ion, and MAA.
Since arsine, methylarsine and, dimethylarsine will volatilize
from the trap in the order of their boiling points, the com-
pounds pass through the detector at different times and the analysis
readout is similar in appearance to a gas chromatogram. Thus, the
two methylated arsenic acids can be distinguished from one another
and from inorganic arsenic. The authors applied this method to the
analysis of water samples, bird eggshells, seashells and limestone,
and adapted this method to the analysis of urine samples.
19
-------
Specific residue methods are outlined below:
Gutzeit Method - (Official Final Action) - (For total arsenic) - The sample
is oxidized to AS205 with a sulfuric and nitric acid mixture, then reduced to
AsH3 by Zn-HCl in SnCl2 and KI. A paper strip soaked in HgBr2 and placed in a
narrow tube develops a stain of a length which can be calibrated for As content
in the sample. A preabsorber with lead acetate removes any H2S evolved.
Special separation techniques are needed following the oxidation step where
interfering substances are present (for example, pyridine in tobacco) or where
the As is difficult to convert to As, as in shrimp (AOAC 1970).
Samples of fresh fruits, dried fruit products, vegetables or other
materials, are treated with nitric and sulfuric acids to convert arsenic
compounds to arsenic pentoxide (AS205) . According to PAM (1967), the sensitiv-
ity of the method is 0.01 to 0.03 mg or about 0.1 ppm.
Colorimetric Methods - (Official Final Action) - For each of the 2 colori-
metric methods, the arsenic compound in the sample is converted to arsine (by
reduction with zinc) and the arsine is absorbed in a reagent which produces a
color (AOAC 1970).
Buttrill (1973) described a colorimetric method for determining arsenic
residues that has been adopted by AOAC as "official first action" for arsenic in
meat and poultry. The method uses the molybdenum blue complex for a spectro-
photometric readout and involves ashing with magnesium nitrate at 600°C. Six
groups of 4 samples were analyzed. The average recoveries for 0.28 to 2.41 ppm
arsenic were 87.6 to 109.3%; the standard deviations ranged from 0.037 to 0.225.
The method is based on the work of Kingsley and Schaf fert (1951^ whose glassware
design is used, and on the sample preparation techniques of Evans and Bandemer
(1954) .
Molybdenum Blue Method - (For total arsenic) AsH3, produced as in the
Gutzeit method, is absorbed in NaOBri and mixed with a solution of (Nlfy) 2*1004
and hydracine sulfate. The color produced is determined spectrophotometrically
(at 845 nm) and is compared to a series of blanks prepared similarly. According
to PAM (1967), the molybdenum blue method has a working range between 0.01 and
0.06 mg of arsenic; the sensitivity of the procedure is 0.1 ppm.
Diethyldithiocarbamate Method - (For total arsenic) The arsine is absorbed
in a solution of silver diethyldithiocarbamate. The color intensity is determined
spectrophotometrically (at 52 nm) and the concentration of arsenic is determined
from a standard curve. According to PAM (1967), the silver diethyldithiocarbamate
procedure has a working range of between 1 and 15 yg of As203- The sensitivity of
the method is estimated to be 0.01 ppm As 203.
20
-------
Dry-Ash Methods - Evans and Bandemer (1954) demonstrated that biological
materials with magnesium nitrate can be ashed in an electric furnace without
loss of arsenic. Stone (1967) modified this procedure to allow arsenic
analysis in animal tissues at a sensitivity of less than 0.1 ppm.
Hudley and Underwood (1970) investigated a simple, sensitive, and reproduc-
ible procedure for the determination of total arsenic in composite food samples.
The samples are dry-ashed in the presence of magnesium oxide and magnesium
nitrate. Arsenic is then evolved from an acid solution as its hydride. The
arsine is reacted with silver diethyldithiocarbamate to give a red complex that
is measured spectrophotometrically. The absorbance of this complex is pro-
portional to arsenic over a wide range of concentrations (1 to 20 yg arsenic).
The method is sensitive to 0.05 ppm arsenic. The procedure of Hundley and
Underwood utilized the dry-ash procedure of Stone. According to Hundley and
Underwood, their method was comparable to the wet-ash procedure and colori-
metric determination used as the "official method." However, they noted that
the official method requires an average of 80 hr for the analysis of the 12
food categories specified in the total diet program; the same number of analyses
may be accomplished in 20 to 24 hr using the method of Hundley and Underwood.
Furthermore, a substantial improvement in recovery is obtained by this method.
Atomic Absorption Methods - There have been significant developments in the
analysis of arsenic by atomic absorption methods. The basis of the new method
is the generation of arsine by treatment of the arsenic sample with sodium
borohydride. The arsine generated is introduced directly into the flame. The
method has been recently described by Thompson and Thomerson (1974) and by
Duncan and Parker (undated). The method apparently has not been used yet for
organoarsenic pesticides, but it would appear suitable for both formulation and
specific residue analyses. The organoarsenic pesticides would require initial
conversion into arsenic oxide by conventional wet digestion or dry-ashing
procedures, then reduction to arsine by aqueous sodium borohydride.
Thompson and Thomerson (1974) reported that the detection limit for
arsenic is 0.8 ng/ml. In precision studies, these investigators observed that
a concentration of 100 ng/ml in 10 separate measurements produced a relative
standard deviation of 5.7%.
'. ,
Duncan and Parker (undated) report a sensitivity of 0.1 ng/ml and an
absolute sensitivity of 2 ng. In a check for accuracy, these investigators
used NBS standard reference material SRM 1571 (orchard leaves) which is certi-
fied to contain 14 ± 2 yg/g of arsenic. Their results showed an analysis of
14.9 ±0.4 yg/g with a relative standard deviation (based on 5 determinations)
of 2.6%.
Formulation Analysis - Only limited information is available concerning analysis
of cacodylic acid formulations. However, any of the residue analysis methods
for arsenic could probably be adapted for formulation analyses. They are
summarized below:
21
-------
AOAC Method for Arsenic in Sodium Cacodylate - Official Final Action -
A method for the determination of arsenic in sodium cacodylate is described.
The method involves a digestion of the sodium cacodylate sample with
potassium sulfate, starch and sulfuric acid. The digested material is
subsequently analyzed using the conventional iodometric procedure (AOAC 1970).
Four other methods, with Official Final Action status, provide analysis
for total arsenic in pesticide formulations. However, the methods either
specify that they are used for inorganic arsenate or arsenites, or only mention
inorganic arsenicals. These methods are the hydrazine sulfate distillation
method, the iodometric method, an ion exchange method, and a water-soluble
arsenic method.
Potential Formulation Analysis. Method - Carey (1968) proposed a formula-
tion analysis method involving a fusion procedure in which the arsonate is
decomposed to pentavalent arsenic by a potassium bromate-nitric acid solution.
He tested the method on MSMA (commercial formulation), DSMA (technical grades),
and several other arsenicals, including arsanilic acid, H2NC6H4AsO(OH)2- Thus,
the method appears to be applicable to cacodylic acid. The fusion temperatures
are preferably kept below 300°C. Color in the fusion mass indicated inter-
ferences; these can be removed using an ion exchange procedure. Carey (1968)
presented actual results for each compound, but did not include an overall
accuracy of the method.
Composition and Formulation
Technical grade cacodylic acid is 65% pure and contains sodium chloride
(Martin 1971). Water is the principal solvent in cacodylic acid formulations.
These usually contain; a surfactant. Based upon patented production methods
(Moyerman and Ehman 1965; Schanhals 1967), technical cacodylic acid also contains
sodium sulfate, sodium chloride, methylarsonic acid, and arsenic acid. No in-
formation is available concerning the quantities of these impurities in commer-
cially available formulations. Both the DSMA feed and the final product in the
Ansul process are free of trivalent arsenic and have none of- the garlic odor
characteristic of cacodyl compounds, arsines, and arsine oxides. Analyses of
the process on a bench scale (Ansul 1975) have shown that neither cacodyl
oxide or arsines are present under the reaction conditions used by Ansul. (See
equations 7, 8, 10, and 15, pp. 13, 15.) Field reports refer to garlic odors from
treated forest sites after 48 hr (Wagner and Weswig 1974) but not from the
formulated products themselves. According to Ansul (1975), it is also possible
that reducing conditions at surfaces of metals, such as iron in storage vessels
could produce traces of cacodyl oxide and a garlic odor. (See equation 22 and
35, pp. 27, 28.)
The formulation used as a tree killer is 50% cacodylic acid (6 Ib/gal).
Formulations are also available with sodium cacodylate and cacodylic acid as
the minor herbicidal ingredients. (See subsection on Formulations, p. 110.)
22
-------
Chemical Properties, Reactions, and Decomposition Processes
Acidic and Chemical Properties - Cacodylic acid is normally considered to be an
acid, but it is actually an amphoteric electrolyte. Reported values of the
ionization constant are presented in Table 1. Definitions for the letter desig-
nations are as follows:
pkg Negative log of kfl
ka For the equation Me2AsOOH + H20 > Me2AsOO~ + H30+,
[Me2AsOO-] [H30+]
ka =
[Me2AsOOH]
kb For the equation Me2AsOOH + H30+ > Me2AsOOH-H+ + H20 ,
[Me2AsOOH-H+]
[Me2AsOOH] [H30+]
kh
Kg = — where
k,, = ionization constant of water = 1 x 10"^ at 24°C.
The pka value of Juillard and Simonet (1968) in Table 1 was that
obtained in a series of determinations using water-methanol mixtures.
Other pka values at various methanol concentrations were: 20%, 6.47;
40%, 6.77; 60%, 7.14; and 80%, 7.64.
According to Hantzsch (1904) (cited by Raiziss and Gavron 1923), conduct-
ivity measurements with cacodylic acid show that, when treated with an excess
of caustic alkali, it does not react strictly as a monobasic acid, but partly
as the sodium salt of a tribasic acid. He concluded that in the presence of
one molecule of sodium hydroxide, the acid is monobasic, but with an excess of
alkali it forms the molecular aggregate Me2As(OH)(ONa)2 so that the acid is
capable of functioning in the tribasic form, Me2As(OH)3.
Plumel, (1948) suggested the use of sodium cacodylate as a buffer for the
pH range of 5.2 to 7.2 in experiments where salts of other weak acids cannot
be used.
23
-------
Table 1. IONIZATION CONSTANTS OF CACODYLIC ACID*
pk
6.
6.
*
*a('C)
4.2 x 10-7(25)
6.4 x 10-7(25)
7.5 x 10-7(25)
5.66 x 10-7(30)
5.33 x 10-7(25)
6.2 x 10-7(5)
26 5.5 x 10-7(25)
15 7.1 x 10-7(24)
The ionization constants and
this report.
kb(25°C) KB
3.4 x 1Q- 13** 34
3.2 x HT13** 32
5.1 x 1C' 13** 51
3.73 x 10"13 37.3
related values are defined in the text of
Reference
a/
d/
b/
c/
d/
e/
f/
E/
** Calculated by Midwest Research Institute (Kansas City, Missouri) using
a/
b/
c/
d/
e/
f/
g/
modern value of k_, 1 x 10~
1.2 x 10-14.
Zawidzki (1903).
Holmberg (1910).
Morton (1928).
Kilpatrick (1949).
Dhar (1913).
Juillard and Simonet (1968).
Jacobson et al. (1972). '
•". References cited used a value of
-------
Because it is amphoteric, cacodylic acid will react with some acids; with
hydrochloric acid it will form Me2As02H-HCl. This compound crystallizes into
leaflets which are readily dissociated into their constituents by water (Raiziss
and Gavron 1923). The structure of this product was examined by Simon and
Schumann (1973). With hydrobromic acid the corresponding product is a very
unstable, syrupy mass. The hydrofluoride corresponds to the formula (Me2As02H-
HF)Me2AsF3 (Raiziss and Gavron 1923). Moyermann and Ehman (1965) also reported
that cacodylic acid reacts with nitric and sulfuric acids, but gave no details
concerning reaction products.
Petit (1941) examined the interaction of hot, concentrated sulfuric acid
with cacodylic acid and other arsenical compounds. The reaction of sulfuric
acid with cacodylic acid was studied at temperatures ranging from 190 to 315°C.
The complex reaction is apparently complete within 10 min at 315°C, but is not
complete after 5 hr at 190°C. Petit was primarily interested in the mechanism
of this reaction; he states that the reaction proceeds as shown in the following
equations.
i (OH)2S04H > MeS04H + MeAs(OH)2
MeAs (OH) 2 + H2S04 > MeAsO(OH)2 + S02 + H20
MeAs (OH) 2S04H —> MeS04H + As (OH) 3
Ahrens and Maass (1968) determined the rate constants for proton
transfer between various acceptor ions and donor molecules. For the
reaction:
C2H302 + Me2AsO2H
Acetate Cacodylic ^2 Acetic Cacodylate
acid acid
at an ionic strength of 1 M and 20°C, ^ was 6.2 x 107 Amol~1sec~1 and
was 1.7 x 10° J&mol~^sec~ .
Clifford (1959) determined an electronegativity value for a large
number of ions. For the cacodylate ion, Me2As02, the electronegativity
was 3.15 (relative scale, 0 to 4).
For possible applications in analysis, Pietsch (1958) determined
the pH at which various metal ions began to precipitate with cacodylic
acid at 0.02 molal concentration. The results are shown in Table 2.
25
-------
Table 2. pH AT WHICH METALLIC IONS ARE PRECIPITATED WITH CACODYLIC ACID
£H Ion precipitated
1 Sn+*
2 V02+2, Bi+3
2.5 Fe+3
3 Hg+
* Hg+2
5 ' zr*; Sn+2, Ti*4, Cr+3
6 Pb+2, Be+2, Y+3, La+3, Mn+2, Cu+2, Al+3
6.5 Fe+2> Ni+2s Zn+2
7 Ce+3, Pd44
7.5 co+2, Cd+2, In+3
8 Mg+2, Th44
/
8.5 ca+2
10 Sr+2,.Ba+2
Metal ions not precipitated were: V+5, Cr46, Mo"*"6, W^6, Rv+3, Rh+3,
In44, Pt44, Av+3, Tl+.
Source: Adapted from Pietsch (1958).
26
-------
Oxidation and Reduction Reactions - Cacodylic acid is very stable toward
oxidizing agents. Reports indicate that cacodylic acid is not decomposed by
the action of fuming nitric acid, aqua regia, or potassium permanganate, even
upon heating (LaCoste 1881, cited by Raiziss and Gavron 1923). Cacodylic acid
is not oxidized by bromine water (Braman and Foreback 1973). However, as
discussed in the Analytical Methods subsection of this report, it is oxidized
to As205 by fuming nitric acid in the presence of concentrated sulfuric acid.
When electrolyzed in alkaline solution, cacodylic acid is also oxidized to
arsenic acid [H3As04 or AsO(OH)3] (Fichter and Elkind 1916, cited by Raiziss
and Gavron 1923).
Cacodylic acid is also unaffected by sulfurous acid, oxalic acid, ferrous
sulfate, nascent hydrogen or other milder reducing agents (Raiziss and Gavron
1923). Noller (1957), however, reported that sodium dimethylarsinate is reduced
by sulfurous acid to give cacodyl oxide. The reported reduction reactions of
cacodylic acid are shown (in unbalanced equation form) in Table 3.
Braman and Foreback (1973) reported that cacodylic acid is reduced to
dime thylarsine, Me2AsH, by sodium borohydride at pH 1 to 2. According to the
authors, the pH requirement indicates that the acid must be in the undissociated
form before it can be reduced to the arsine.
Reactions of Cacodylic Acid and Sodium Cacodylate to Form Other Salts - Cacodylic
acid and sodium cacodylate react with many substances to form a variety of salts.
These salts and methods for their preparation are presented in Table 4. Raiziss
and Gavron (1923) also reported that cacodylic acid salts of lithium, barium,
magnesium, iron, strychnine, codeine, and antipyrine have been prepared.
Other Reactions - Jacobson et al. (1972) noted that cacodylic acid is often used
with an appropriate cation to buffer enzyme-catalyzed reactions. They investigated
the interaction of cacodylic acid with thiols, which are commonly used in enzyme-
catalyzed reactions. Although they did not determine the structure of any of
the products formed, they concluded that cacodylic acid and thiols do react.
Compounds studied included 2-mercaptoethanol, cysteine, glutathione and dithio-
threitol. The authors indicated that the reaction was extremely complex, but
concluded that more than one thiol group reacts with each molecule of cacodylic
acid.
Heinemann (1919) reported that, at 120°C, the acid reacts with easily-
meltable condensation products of phenols and formaldehyde, forming resinous
substances in which the arsenic is held in an esterlike combination. These form
water-soluble salts with alkalis, and are soluble in the same solvents as the
parent phenolic condensation compounds, upon which their melting points are also
dependent.
According to Moyermann and Ehman (1965) arsinic acids (which would include
cacodylic acid) form esters with alcohols and organic acid anhydrides. Levskaya
and Kolomiets (1967) also studied the esterification of arsonic acids. When
27
-------
Table 3. REDUCTION REACTIONS OF CACODYLIC ACID
(Equations are not balanced)
Me2As02H + H3P03 A -^ (Me2As)20 (22) Source
Phosphorous Cacodyl a,b/
acid oxide
(23)
Stannous Dimethyl- a»b/
chloride chloroarsine
2N Me2AsAsMe2 + Me2AsH (24)
eectrolysis a,b/
Cacodyl Dimethylarsine
2(CH3)2AsH + 02 _ \ [(CH3)2As]20 + H20 ..... (25)
a,b/
H3P02 -^. (CH3)2AsAs(CH3)2 (26)
HCL ^ a,b/
Cacodyl
Me2As02H (dry) + HI -^ Me2AsI + I2 + H20 + Heat (27)
~• a,b/
Dimethyliodoarsine
Me2As02H (dry) + HBr ^ Me2AsBr + Br2 + H20 + Heat (28)
DimethyIb romoarsine
Me2As02H (dry) + HC1 ^ MeAsCl2 + CH3C1 (29)
Methyldi Methyl ~
chloroarsine chloride
Me2As02H H-;H2S \ (Me2As)2S + S + H20 "(30)
Cacodyl
sulfide
28
-------
Table 3. (Continued)
Me2AsO H + H-jPC^ in HCl
Me2As02H + H3P03 in HBr
Me2As02H + S02 in H2S04
in presence of KI
-> Me
Me2AsBr
(32)
Source
sJ
£/
Me2As02H + S02 + HCl •
2 Me2As02Na + 2 H2S03
KI
;)20 + H20 + 2 NaHS04
(35)
cacodyl oxide
3 Me2AsCl + 3 POC13 (36)
+ H3P02
No atm.
Me2As02H + 2 Zn + 4HC1 * fr0 > Me,AsH + 2 ZnCl2 (37)
4°-45 2+2H20
3 Me2As02H + 4PC13
fj
a/ Fichter and Elkind (1916).
b_/ Raiziss and Gavron (1923).
cj van der Kelen and Herman (1956).
d./ Feltham et al. (1967).
je/ Noller (1957).
f/ Laughlin (1965).
^/ Feltham and Silverthorn (1967).
29
-------
Table 4. REACTIONS OF CACODYLIC ACID OR SODIUM CACODYLATE
U)
O
Product
Me2As02Ag
(Me2As02)2Hg
(Me2As02)2Cu-7CuCl2
(MeAs02)3Bi'8H20
Bismuth cacodylate
^ and
zinc cacodylate
cacodyl oxide
S«CSHC3H5-Me.,As02H
XH2 " '
Thiosinamine cacodylate
Starting materials
Acid and Ag20 or
Acid and freshly precipitated
Hg
Alcoholic solutions of acid
and CuCl2
Strong, hot, saturated solu-
tion of acid with
Acid and Zn
Acid and thiosinaraine
CH?CHCH;,NHCSNH.,
Acifl nnd PCU
Conditions, type of reaction
or nature of product
Dissolve pure oxide or carbonate
in acid; forms long needles
which are soluble in water and
darken in sunlight. Product
reacts with free acid to form
Me2As02Ag • 2Me2As02H
Dissolve HgO in an excess of a
concentrated solution of the
acid. Crystallizes in fine
white needles which yield
mercury when heated.
Mix solutions; shiny green
sediment forms at first
which becomes granular on
boiling. Soluble in water.
Decomposes on heating to
yield cacodyl, copper
chloride, copper arsenite,
arsenic, and carbon.
Product deposits on cooling,
m.p. 82°, 21% soluble in
H20 at 12°, soluble in
alcohol and glycerol-
Product Is a crystalline com-
pound, m.p. 74°; readily
soluble in water or alcohol.
Reference
a.b/
a.b/
a.b/
k/
b/
Cac;xlv) tiiclilnrldv
Me = Methyl group (CH3)
Acfd£= Cacodylic acid = Me2As02H
Salt ° Sodium cacodylate
-------
Table 4. (Continued)
Product
Me2As02Ag
Silver cacodylate
Zn(Me2As02)2-7H20
Zn(Me2A902)2'H20
(Me2As02)2Ca
(Me2As02)2Sr
(Me2As02)Cd'10H20
(Me2As02).,SnMe2
Me2As02PbCl(C6H5)2
Starting materials
Salt and AgN03
Wet Ag20 into 88% aq. acid
Acid, ZnO, and water
Acid and Ca(OH)2
Acid and Sr (OH)2
Acid + Cd(OH)2
Acid + Me2SnCl2
Salt trihydrate +
Sale trihydrate + (C$H5)2PbCl2
Conditions, type of reaction
or nature of product
Double decomposition.
After 12 hr, add 3 vol of
C^OH, filter off first crop
of crystals after 24 hr.
Septahydrate farmed when
evaporated at 15°. '
Monohydrate formed when
crystallized after
evaporating the solution to
half its volume at 50°,
under 70 mm pressure.
Mono- and nona-hydrates, an-
hydrous precipitate.
Mono-, tri-, and •ttitde.cahy- ;:•'-
drates. ''
Fine, silky, colorless crystals
separate. Various hydrated
forms can form under
different conditions of
temperature and pressure.
Product soluble in water and
acids. Decomposes at 330°.
Refluxed in MeOH, 73% yield.
Refluxed in dimethylformamide,
77% yield.
Reference
d/
e/
f/
±/
i/
-------
Table 4. (Continued)
Product
Me3AsS (I), (Me2As)2S (II),
and Me2AsSO (III)
Starting materials
Acid and CS2
Acid + Zn SO/.
Conditions, type of reaction
or nature of product
Heated at 150° for 18 hr. Crys-
tallization from hexane gave
I (11% yield). Removal of
solvent and distillation gave
II (51% yield) and III (25%
yield). fl
••• — i. <»-•'..
Reaction in ethyl alcohol, be-
comes polymerized In C6H6
Reference
I?Bunsen (1843).
b/ Raiziss and Gavron (1923).
cj Clausmann (1923).
&l Zappi and Manini (1929).
B./ Tiollais and Perdreau (1937).
£ ft Tiollais (1936).
Sj Tiollais et al. (1939).
W Chamberland and MacDiarmid (1961).
il Henry (1962).
I/ Reichle (1962).
k/ Ciana (1967).
-------
was heated with butyl alcohol (BuOH) and refluxed in CgHg, the ester,
was formed.
Coates and Mukherjee (1964) treated trimethylgallium (Me~Ga) , with
cacodylic acid dissolved in benzene. The product was dimethylgallium dimethyl-
arsinate, (Me2As02GaMe2)2- The melting point of this product was 144 to 145°C
after sublimation at 110 °C and 0.01 mm pressure.
Occurrences of Residues in Food and Feed Commodities
FDA monitors pesticide residues in the nation's food supply through 2
programs. One program, commonly known as the "total diet program," involves
the examination of food ready to be eaten. This investigation measures the
amount of pesticide chemicals found in a high-consumption varied diet. The
samples are collected in retail markets and prepared for consumption before
analysis. The other program involves the examination of large numbers of
samples, obtained when lots are shipped in interstate commerce, to determine
compliance with tolerances. These analyses are complemented by observation
and investigations in the growing areas to determine the actual practices being.
followed in the use of pesticide chemicals.
A majority of the samples collected in these programs are categorized as
"objective" samples, which are not considered to contain excessive residues or
misused pesticide chemicals. All samples of imported foods and fish are
categorized as "objective" samples even though there may be reason to believe
excessive residues may be found on successive lots of these food categories.
Market-basket samples for the total diet studies are purchased from
retail stores, bimonthly, in 5 regions of the United States. A shopping guide
listing 117 foods for all regions is used, but all foods are represented
differently because of differences in regional dietary patterns. The food
items are separated into 12 classes of similar foods (including dairy
products; meat, fish and poultry; legume vegetables; and garden fruits) for
more reliable analysis and to minimize the dilution factor. Each class in
each sample is a "composite." The food items and the proportion of each used
in the study were developed in cooperation with the Department of Agriculture's
Household Economics Research Division and represents the high consumption
level of a 16- to 19-year old male. Each sample represents a 2-week supply of
food.
33
-------
Surveillance samples are generally collected at major harvesting and
distribution centers throughout the United States and examined in 16 FDA
district laboratories. Some samples may be collected in the fields immediately
prior to harvest. Surveillance samples are not obtained in retail markets.
Samples of imported foods are collected when offered for entry into the United
States.
The residue analysis currently being used by FDA does not detect cacodylic
acid as an individual chemical. Residue analyses are made for total arsenic in
the form of As20~, but the analytical method does not distinguish between
naturally occurring arsenic or arsenic resulting from the presence of any of
the arsenical pesticides.
Table 5 presents the results of total diet program for a 6-yr period. The
number of composites which were found to contain arsenic and the concentration
ranges (ppm) are illustrated. Although the FDA has continued the analytical
program, results have not been reported since the 1969 to 1970 study was
published in 1972.
The information in Table 5 was used to calculate the daily intake of
arsenic shown in Table 6. Duggan and Corneliussen (1972) drew the following
conclusion for the 6-yr period:
The incidence and levels of As00 have remained low during the 6
years of this study. While there is a wide variation in the actual
annual range, the differences generally are due to higher values for
a few samples examined during a particular year. There is a natural
low-level background of arsenic in foods, and the values reported
during this period are within or slightly above the natural background.
The dietary intake of arsenic from pesticide use does not appear to be
significant.
Acceptable Daily Intake
The acceptable daily intake (ADI) is defined as the daily intake which,
during an entire lifetime, appears to be without appreciable risk on the basis
of all known facts at the time of evaluation (Lu 1973). It is expressed in
milligrams of the chemical per kilogram of body weight (mg/kg).
The ADI for pesticides is established jointly by the Food and Agricultural
Organization Committee on Pesticides in Agriculture and the World Health Organi-
zation Expert Committee on Pesticide Residues. However, an ADI for cacodylic
acid (or for arsenic) has not yet been established.
34
-------
Tolerances
Section 408 of the Food, Drug and Cosmetic Act, as amended, gives
procedures for establishing U.S. tolerances for pesticide chemicals on raw
agricultural commodities. Section 409 applies to food additives, including
pesticide chemicals on processed foods. Tolerances for cacodylic acid,
calculated as As203» are publisehd in the Code of Federal Regulations (Section
180.311). They are: 2.8 ppm in or on cottonseed; 1.4 ppm in the kidney and
liver of cattle; and 0.7 ppm in the meat, fat, and meat by-products (except
kidney and liver) of cattle.
35
-------
Table 5. ARSENIC IN TOTAL-DIET SAMPLES^:/
Year of study
Date of study!!/
Number of composites
Dairy products
Meat, fish and poultry
Grain and cereal products
Potatoes
Leafy vegetables
Legume vegetables
Root vegetables
Garden fruits
Fruits
Oils, fats and shortening
Sugar and adjuncts
Beverages
Totals (concentration
1*'
1964-1965
18
1
1
1
1
1
1
6
— —
(0.12)
(0.10)
(4.7)
—
(0.11)
(0.10)
—
(0.18)
—
--
--
(0.1-4.7)
5
1
1
1
1
10
Z£/
1965-1966
28
..
(O.lrO.5)
(0.1)
--
--
—
(0.1)
(0.1)
—
—
(0.1)
--
(0.1-0.5)
9
2
3
3
2
4
33
3d/
1966-1967
30
i/
(0.1-0.5)
i/
—
1
(max. 0.18)
(max. 0.16)
—
(0.1-0.2)
(0.1)
(max. 0.15)
—
(0.1-0.4)
4«/
1967-1968
30
i/
16 (0.1-0.6)
5 (0.1-0.8)
8 (0*1-0.2)
6 (0.1-0.3)
1 (0.2)
2 (0.1)
4 (max. 0.2)
5 (0.1-0.5)
3 (0.1-0.4)
6 (0.1)
5 (0.1-0.2)
65 (0.1-0.8)
15
7
3
4
3
3
4
5
2
5
3
57
5l/
1968-1969
30
i/
(0.1-1.0)
(0.1-0.2)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1)
(0.1-1.0)
6&/
1969-1970
30
i/
14 (0.1-2.
--
2 (0.1)
—
--
1 (0.2)
1 (0.'2)
1 (0.2)
--
—
--
21 (0.1-2.
6)
6)
ranges, ppm)
a/ The values are the number of composites which were found to contain arsenic. The concentration, range or
maximum value of arsenic (in ppm) is given in parenthesis. The absence of a value in parenthesis
indicates that this information was not available. A dash indicates that none of samples contained
arsenic.
b/ Duggan et al. (January 7, 1966).
c/ Duggan et al. (September, 1967).
d/ Martin and Duggin (March 1968).
e/ Corneliussen (March 1969).
fj Corneliussen (December 1970).
Sj Corneliussen (March 1972).
h/ June of first year to April of second year, samples taken bimonthly.
±/ Arsenic was stated to be present, but neither the number of composites nor the concentration range was given.
-------
Table 6. DAILY INTAKE OF ARSENIC RESIDUES^/
to
Date of studyk'
Dairy products
Meat, fish and poultry
Grains and cereals
Potatoes
Leafy vegetables
Legume vegetables
Root vegetables
Garden fruits
Fruits
Oils, fats and shortening
Sugar and adjuncts
Beverages
1964-1965£/
— —
< .001
0.002
0.063
—
0.001
0.001
—
0.002
—
--
—
1965-1966£/
-------
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PART II. INITIAL SCIENTIFIC REVIEW
SUSPART B. PHARMACOLOGY AND TOXICOLOGY
CONTENTS
Page
Acute, Subacute and Chronic Toxicity 46
Toxicity to Laboratory Animals 46
Acute Oral Toxicity - Rats 46
Subacute Oral Toxicity - Rats 47
Subacute (Dietary) Toxicity - Rats 48
Acute Dermal Toxicity - Rabbits 48
Eye Irritation - Rabbits 48
Skin Irritation - Rabbits 49
Primary Skin Irritation - Rabbits 49
Subacute Dermal Toxicity - Rabbits 49
Subacute (Dietary) Toxicity - Dogs 50
Toxicity to Domestic Animals 50
Acute Toxicity - Cattle 50
Subacute Oral Toxicity - Cattle 51
Subacute Oral Toxicity - Sheep . . . ,, 52
Subacute Oral Toxicity - Chickens 52
Toxicity to Man 52
Occupational Hazards 52
Accidents 53
Symptomology and Pathology 53
Animals 53
Man 54
Metabolism 54
Absorption and Excretion 54
Tissue Accumulation 56
Mutagenic Effects 56
Oncogenic Effects 57
Teratogenic Effects 57
References 58
45
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This section reviews data on the acute, subacute and chronic toxicity of
cacodylic acid in laboratory and domestic animals. Symptomology and Pathology
in animals and man is discussed. The metabolism of cacodylic acid is also
reviewed. Mutagenic and oncogenic effects are presented. The section sum-
marizes rather than interprets data reviewed.
Acute, Subacute, and Chronic Toxicity
Toxicity to Laboratory Animals -
Acute Oral Toxicity - Rats - Male albino rats were tested for toxic suscepti-
bility to a herbicide formulation that contained 77% cacodylic acid. The
material was administered by stomach tube to rats that weighed 200 to 300 g.
The animals were observed for 14 days after treatment. An LD5Q of 700 mg/kg
was calculated from the results of this test (Nees 1960).
The toxicity to rat's of a herbicide composed of 61.29% cacodylic acid as
the active ingredient has also been reported. Sprague-Dawley albino rats were
used in this study. Six dose levels were administered to male and female rats
in test groups of 8 animals each (4 males and 4 females for each dose). The
herbicide was given to the rats as a 20% aqueous solution administered directly
to the stomach by a syringe. The animals were observed for 14 days following
treatment. The LDcQ for males was 1.4 g/kg (1.15 to 1.71) and for females
was 1.28 g/kg (0.93 to 1.75).
Within 1 hr, some animals developed diarrhea, which continued for 24 to
48 hr; after 48 hr, survivors were all normal. Death occurred in susceptible
animals within 24 hr. Necropsy did not reveal any gross pathological changes
(Kay 1961).
An approximate LD^Q was determined for a cacodylic acid herbicide (AnsarvS'
160) to rats. The material tested contained 24.78% sodium cacodylate and 8.76%
cacodylic acid (cacodylic acid equivalent = 30.13%). Adult albino rats (200
to 300 g Sprague-Dawley strain) were used in the tests. Their reactions,
following treatment by intubation, were observed for 2 weeks. An approximate
oral LD50 of 3.2 ml/kg was calculated from the mortality data. Two animals
were used at each dose level (Nees 1965).
A herbicide formulation containing 25.1% cacodylic acid was tested for
toxicity to young albino rats (150 g). Four males and 4 females were used in
each group at each dosage level. The material was given by intubation and
the animals were observed for 14 days following treatment. An acute oral
LD50 of 2.6 g/kg (2.1 to 3.2) was calculated from the mortality data. An
LDQ.01 of °-92 g/kg and an LD99.99 of 7'4 g/kg were also reported.
46
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A slight loss of body weight was noted during the surveillance period.
Necropsy of dead animals did not reveal any gross pathological alteration
in any tissue or organ that could be attributed to treatment (Palazzolo
1965).
Charles River strain rats were given doses of a formulation containing
27.38% sodium cacodylate and 4.67% cacodylic acid (32.05% cacodylic acid
equivalents). The LD50 value was found to be 2,480 mg/kg, with standard
deviation of 412.0 mg/kg. Necropsy examination of animals that died showed
hemorrhaging in the gastrointestinal tract. No gross pathology was seen in
animals sacrificed after the 14-day observation period (Industrial Bio-
Test Laboratories 1975).
A summary of the acute oral toxicity data of various cacodylic acid
formulations to rats is given in Table 7.
Table 7. ACUTE ORAL TOXICITY TO RATS
Formulation :
LD5Q (95% CI) LDQ.01 ^099.99
% cacodylic acid Sex
25.1
32.05
30.13
77.0
61.29
61.29
61.29
M and F
M and F
M and F
M
M
F
M and F
(g/kg)
2.6 (2.1-3.2)
2.48 (4.2.0)
approximately
3.2 ml
0.70
1.4 (1.15-1.71)
1.28 (0.93-1.75)
1.35 (1.11-1.64)
(g/kg)
0.92
0.82
0.38
0.48
(g/kg)
7.4
2.41
4.3
3.9
Reference
Palazzolo (1965)
Industrial Bio-
Test Laboratories
(1975)
Nees (1963)
Nees (1960)
Kay (1961)
Kay (1961)
Kay (1961)
Subacute Oral Toxicity - Rats.. - Weanling rats (Sprague-Dawley strain, 40
to 50 g) were fed a basal ration containing a herbicide that consisted of 77%
cacodylic acid. Three groups of 10 rats each were diet-fed cacodylic acid at
levels equal to 40, 20 or 10% of the estimated LD5Q (0.7 g/kg). A control group
was fed only basil ration. Feeding was continued daily for 20 days. At the
end of the feeding period, all animals were sacrificed for histological examina-
tion. The tissues examined were the cerebrum, cerebellum, heart, lungs, liver,
spleen, kidney, adrenals, pancreas, stomach, small bowel, large bowel, testes,
urinary bladder, and bone.
47
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Changes in tissues were not seen in animals fed at the 20% or lower
level or in controls. There was some evidence in animals fed at 40% of the
LD5o of reduced activity of spermatogonia cells and some atrophic changes in
the seminiferous tubules (Nees 1960).
Subacute (Dietary) Toxicity - Rats - Weanling rats (Sprague-Dawley strain)
were given cacodylic acid at dietary levels of 3, 15, 30 and 100 ppm for 30
days. Both male and female rats were treated at each of 6 dietary levels; a
control group fed an untreated diet was also included.
After 90 days of feeding, urinalysis and hematological studies were done
on 5 animals of each group. All animals were sacrificed for gross pathology.
A comparison of the responses of each group of animals indicated that there
were no significant differences in body weight or food consumption between the
controls and the test animals. Variations in the results of the hematological
examinations and the urinalysis could not be attributed to cacodylic acid
treatment. There were no differences between treated and control animals in
organ weights. The histological alterations that were observed were minimal
and were reported to be of a type generally found in laboratory rats of the
age of those tested (Nees 1968).
Acute Dermal Toxicity - Rabbits - A group of 2 male and 2 female albino
rabbits had shaved skin of their backs exposed to 3,000 mg/kg Bolls Eye (32.05%
cacodylic acid) for 24 hr. The animals were wrapped with impervious plastic
and tape to prevent oral ingestion of test material. After 24 hr, the plastic
tape and test material were removed.
An acute dermal LD5Q value of greater than 3000 mg/kg was estimated. All
rabbits lost a slight amount of weight during the first week after exposure,
but they showed normal weight gain during the remainder of the 14-day observa-
tion period. No toxic signs were noted, and skin changes were seen as moderate
edema at 24 hr and slight desquamation at days 7 and 14. With the exception
of skin changes, there were no other pathological changes observed (Industrial
Bio-Test Laboratories 1975).
Eye Irritation - Rabbits - A 0.1 ml amount of undiluted Bolls Eye (32.05%
cacodylic acid equivalent) was instilled into the conjunctive sac of the right
eye of each albino New Zealand strain rabbit tested. The left eye was used
as a scoring control. Injuries and their persistance in the conjunctiva,
cornea, and iris were used to score, with 110 representing maximum irritation
and 0 representing no irritation. Classifications into corrosive, irritating,
and nonirritating were made, and the Bolls Eye formulation was considered
nonirritating (Industrial Bio-Test Laboratories 1975).
In another study, New Zealand albino rabbits were used in eye irritation
tests in which test animals were constrained during the test period so they
could not rub their eyes. A 0.1 ml portion of a formulation which contained
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77% cacodylic acid and 22.8% sodium chloride was placed in one eye of each
test animal. The untreated eye was used as a control. Six rabbits were
treated; 3 had the eye washed with 20 ml of water 2 to 4 hr after introduction
of the herbicide. Under test conditions, the herbicide formulation containing
77% cacodylic acid had an ocular irritation score of 2.0. The author con-
cluded that a score of 2.0 placed the material in the "essentially nonirrita-
ting" category (Nees 1960).
Skin Irritation - Rabbits - In one study, 4 areas were clipped on the
backs of albino rabbits (10 cm apart) and used as test sites for determining
dermal irritation. Two areas on each rabbit were left intact and 2 were
abraded. A formulation containing 77% cacodylic acid was applied to 6
immobilized rabbits, and the treated areas were covered for 24 hr. Under
test conditions, the herbicide had a primary irritation index of 0.3 and, at
this level, was considered "essentially nonirritating" to the skin (Nees 1960).
Primary Skin Irritation - Rabbits - Albino New Zealand strain rabbits
were used to determine the primary skin irritation resulting from exposure
of clipped intact and abraded skin to Bolls Eye (32.05% of cacodylic acid
equivalent). A 0.5 ml amount of undilute Bolls Eye was applied to each test
site, and the site was immediately occluded by a 2 in square gauze patch
secured by masking tape. The rabbit's trunk was then wrapped in plastic. The
tests were observed at 24 and 72 hr. The study demonstrated that Bolls Eye
is nonirritating (Industrail Bio-Test Laboratories 1975).
Subacute Dermal Toxicity - Rabbits - Adult male albino rabbits (2 to 3
kg) were used to test whether or not a cacodylic acid herbicide caused skin
irritation, sensitization, or mortality. Two animals were tested at each
dosage level under 2 conditions: normal skin (clipped) and abraded skin (clip-
ped) . A herbicide formulation containing 77% cacodylic acid was used in the
test, and it was applied to the skin as an aqueous suspension by inunction.
Exposure was continued for 12 hr. Each animal was treated 5 days a week for
3 weeks, and observations were carried out for 2 weeks following the final
treatment.
Sensitization was tested by 1 application of the herbicide to new skin
areas of survivors after 10 to 14 days. Necropsies were performed on all
dead animals. Two tests were run in this series, 1 at dose levels of 3.9, 6.0,
and 9.4 g/kg; and the other at 1.0, 1.6, and 2.5 g/kg.
The clinical signs of intoxication noted were: rapid loss of conditioning,
diarrhea, and mild hyperemia on application areas on intact skin and severe
hyperemia with apparent cyanosis on margins of abrasions.
A summary of the mortality associated with the various doses is shown in
Table 8.
49
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Table 8. DERMAL TOXICITY (MORTALITY) OF A HERBICIDE
(77% CACODYLIC ACID) TO RABBITS
Dose (g/kg)
Condition of skin 1.0 1.6 2.5 3.9 6.0 9.4
Normal O/l3/ 0/l£/ 1/1 (13)>-/ 1/1 (13) 1/1 (5) 1/1 (4)
Abraded 1/1 (5) 1/1 (3) 1/1 (2) 1/1 (9) 1/1 (5) 1/1 (2)
a./ Weight loss noted.
b_/ Figures in parentheses are days of death.
Necropsy indicated that"fluid accumulation in the intestinal tract was
the most commonly found sign of intoxication. The spleen often showed vascular
congestion, and there was distention of the large bowel in many instances.
Animals that died from the heavier dosage had a heavy inflammatory infiltrate
of a mixed type directly beneath the epithelium and parenchymatous degeneration
deep in subcutaneous tissue. No evidence was obtained for sensitization
(Nees 1960).
Subacute (Dietary) Toxicity - Dogs - Thirty-two beagle puppies were
divided into 4 groups of 4 males and 4 females each. One group was used for
controls, and the other 3 were given dietary levels of cacodylic acid (100%)
of 3, 15, or 30 ppm. Body weights were recorded weekly. Kidney and liver
function tests and urinalyses were conducted after 90 days feeding.
Mortality was not noted in any of the test groups. No differences in body
weights at 30 ppm were observed with the exception of a slower weight gain
for females. Hematological differences between treatment and control groups
were not detected, and there were no real differences apparent between control
and treated animals . Some lesions were noted in brain, heart, liver, kidney,
spleen, intestine, and other organs, but the lesions were randomly scattered
in both control and test animals and were not considered to be due to diet
supplementation with cacodylic acid (Derse 1968).
Toxicity to Domestic Animals -
Acute Toxicity - Cattle - Holstein dairy calves were treated with acute oral
doses of Ansar 160 (24.78% sodium cacodylate and 8.76% cacodylic acid) and Ansar
560 (22.73% sodium cacodylate and 3.88% cacodylic acid) to determine minimum
lethal dose or LD5Q values. One animal per dose was used, and treatment levels
were increased until lethal dose was found. Three additional calves were treated
50
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with ..he "minimum lethal dose," and signs of toxicity were noted. Dosages
were determined on the basis of milligram elemental arsenic per kilogram
body 'eight.
The value found for Ansar 160 was 254.0 mg/kg and 200.0 mg/kg for Ansar
560. Treated calves had diarrhea accompanied by general listlessness and
inanition. Signs appeared 24 to 36 hr after treatment and persisted from 4
to 5 days in the surviving animals (The Ansul Company undated).
Subacute Oral Toxicity - Cattle - Two cows were fed for 60 days on cotton-
seed meal ration containing 10 ppm of cacodylic acid. At a feeding rate of
5.4 Ib of cotton seed meal per day, the animals received a daily intake of
24.5 mg cacodylic acid. At this level of intake, mortality did not occur.
When the animals were slaughtered after 60 days feeding, tissue levels of
arsenic were low, with the principal sites of storage being the liver, spleen,
and pancreas. Cacodylic acid residues were not detected in the milk. Ex-
cretion of cacodylic acid was primarily by urine (75 to 80%) and a balance
between intake and output was established after 30 days feeding. (Peoples
1963).
Cattle were also treated by capsule or by drench with a commercial
herbicide formulation (26.5% cacodylic acid) at dosages from 5 to 50 mg/kg
body weight. Doses were given daily up to 10 days. When dosing was done
by capsule, no ill effects were noted up to the maximum dose given (25 mg/
kg). When dosing was accomplished by drench, an irritation effect was
reported for the 10 mg/kg level after the second dose (unrelated to toxicity
action) and a 5% weight loss occurred after 10 doses. At 25 mg/kg, the drench
resulted in apparent poisoning after 8 doses; however, the animal survived
10 doses. Drenching at 50 mg/kg resulted in obvious poisoning after the first
dose, and death occurred 4 days after the seventh dose (U.S. Department of
Agriculture 1972).
In another study, 6 Holstein dairy calves (2 per dose) were fed doses of
200.3, 400.6, and 1201.8 mg/kg Ansar 560 (22.73% sodim cacodylate and 3.88%
cacodylic acid) for 7 days. Dose levels corresponded to 10%, 20%, and 60% of
the estimated LDjQ value and are expressed on the basis of mg of product per
kg of body weight.
All calves fed cacodylic acid showed decreased feed consumption. Calves
given the 10% diet continued eating some of their daily ration throughout the
7 day test. Calves on the 20% diet refused their feed after the fifth day;
those on the 60% diet refused feed after the fourth day. One calf given the
60% diet had diarrhea, and the other in the group died. The authors attributed
the death to "the rapidity of feed consumption." When the calves were returned
to pretreatment diets their feed consumption rapidly returned to a normal daily
rate (The Ansul Company undated).
Another study is considered in the Fate and Significance in the Environment
section on the exposure of cattle grazing in forest areas treated with MSMA and
other arsenical herbicides.
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Subacute Oral Toxicity - Sheep - Mortality or poisoning was not observed
in sheep when dosed from 10 to 25 mg/kg (26.5% cacodylic acid) whether the dose
was given by capsule or drench. Treatment by capsule at 50 mg/kg, however, re-
sulted in an apparent poisoning in one animal after 3 daily doses. The animal
survived 10 doses but exhibited a 21% weight loss. A second sheep dosed at 50
mg/kg by capsule also survived 10 doses but suffered a 22% weight loss. Signs
of poisoning were observed after the second dose (U.S. Department of Agricul-
ture 1972).
Subacute Oral Toxicity - Chickens - Three groups of 23-week-old white leg-
horn chickens (7 females and 3 males per group) were fed cacodylic acid in a
basal diet for 10 weeks. Three levels of cacodylic acid were tested: (a) 0.3
ppm dietary arsenic, (b) 3.0 ppm dietary arsenic, and (c) 30 ppm dietary arsen-
ic. After 1 month of feeding, eggs were collected from each hen for a 3-day
period; after 2 months, additional eggs were gathered. After 10 weeks, 3 fe-
males and 2 males from each group were sacrificed, and selected tissues were
analyzed for arsenic. The animals not sacrificed were then placed on a caco-
dylic-free diet for 7. days; these animals were sacrificed after the 7-day re-
covery period, and selected tissues (fat, abdominal; liver, all; muscle, 50%
white and 50% dark; and kidney) were analyzed for arsenic content. Eggs from
hens fed at 30 ppm dietary arsenic contained 0.22 ppm at 1 month and 0.23 ppm
at the end of the second month (Bodden 1968).
A commercial herbicide containing 26.5% cacodylic acid was administered
(by pipette) to chickens in doses ranging from 50 to 500 mg/kg body weight.
Ten daily doses were given; 5 chickens were used at each dose level. During
the time this experiment was in progress, the untreated controls exhibited a
53% weight gain. The chickens treated with up to 100 mg/kg appeared to match
the- gain of the controls. The 2 groups treated at 175 and 250 mg/kg had a
lowered weight gain (33 and 36%, respectively) and the group treated at 500
mg/kg exhibited the lowest gain of all (13%). While weight gain was affected,
there were no mortalities, even at the highest treatment level (USDA 1972).
Toxicity to Man - No specific information was found on acute, subacute or chron-
ic toxicity of cacodylic acid to man by oral, dermal, or respiratory routes.
Occupational Hazards - The occupational hazard to forestry workers in the
use of cacodylic acid for tree-thinning operations was reported by 2 groups
of investigators. Tarrant and Allard (1972) used 3 tree-thinning crews in one
study to determine the exposure hazard related to the use of cacodylic acid
and another arsenical over a 9-week period. The study was carried out during
the summer. In order to minimize variation in exposure, all subjects in the
study were required to wear similar clothing and to follow recommended safety
practices. Urine samples were collected on Monday mornings before work was
begun, and again on the following Friday afternoon at the end of the working day.
Six men were assigned to each test crew; one did not work with any of the
chemicals and served as a reference. The other 5 crewmen used either cacodylic
52
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acid or another organic arsenical herbicide and applied it by use of an inject-
tor hatchet, an injector tool, or by the hack-squirt method.
There was no statistical significance in differences in urinary levels of
arsenic among crewmen using cacodylic acid, those using another organic arsenical
herbicide, and those using alternative application methods.
The levels of arsenic in the urine of the workers were elevated after 1
week of exposure. The values were higher on Fridays but in most instances
were normal by the following Monday. There was no indication of a continuing
increase over the 9-week study period.
All but one of the 15 men applying the chemicals in this study had urine
arsenic levels in excess of 0.3 ppm at least once during the test. The highest
level recorded was 2.5 ppm. No health problems were observed that could be
related to arsenic poisoning.
Wagner and Weswig (1974) examined forestry workers exposed to cacodylic
acid during tree-thinning operations for evidence of arsenic accumulation in
urine. It appeared that urinary excretions were adequate for use as an index
of exposure, but blood levels correlated poorly with exposure. This study
indicated that workers exposed to organic arsenicals will show positive evidence
of exposure by analysis of the 24-hr urinary excretion during the first week
of exposure. In contrast to the results of Tarrant and Allard (1972), none
of the workers in this study exceeded a urinary concentration of 0.3 ppm.
Accidents - Accidental exposure to cacodylic acid during its use is
apparently quite limited. Data from the EPA Pesticide Episode Review System
(PERS) shows that only one episode, including those involving humans, animals,
and plants as well as episodes involving area contamination, was reported
from 1972 to 1974.
Symptomology and Pathology -
Animals - Some or all of the following signs may be observed in animals
acutely or chronically affected by arsenic compounds: loss of condition
(rough hair coat), loss of body weight, diarrhea, evidence of abdominal pain,
cutaneous hyperemia, increased sensitivity of the skin, teeth grinding,
stiffness of limbs, loss of coordination, posterior paresis, and quadriplegia
(Ledet et al. 1973; Jones 1958; Weaver 1962).
Gross pathological examination of animals may lead to an observation of
liver and kidney alteration with small areas of kidney herrhages evident,
and perhaps some liver degeneration. The heart may be congested. There will
likely be extensive fluid accumulation in the intestinal tract, and this will
probably be the most commonly found condition.
53
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Man - In man, the usual signs of organic arsenic poisoning will probably be
those most often noted in cases of poisoning by inorganic arsenicals. Some of
these are: burning pain in esophagus and stomach, nausea and vomiting, diarrhea
followed by bloody discharges, muscular cramps, vertigo, cold clamy skin and
cold extremities, numbness of feet which may spread to upper limbs, burning
sensation in limbs or other affected areas, tenderness in muscles or lack of
joint sense, pigmentation of skin (raindrop), hyperkerotosis of palms and
soles, stupor, circulatory collapses, convulsions, coma, polyneuropathy (2 to
3 weeks), development of Mee's lines (6 weeks) (Merck 1966; Munasingle et al.
1969).
Metabolism
Most of the studies reporting on the metabolism of arsenic compounds were
concerned with arsenicals other than cacodylic acid. Some of the more pertinent
of these reports have been included in this section because the results may
hold some indirect evidence for the metabolic fate of cacodylic acid.
Absorption and Excretion - The results of a study by Hwang and Schanker (1973)
indicate that cacodylic acid is absorbed from the small intestine of rats at
rates such that 50% of a dose will be absorbed in 1.5 to 3.4 hr.
The mechanism by which cacodylic acid was absorbed appeared to be simple
diffusion. The absorption process did not show evidence of saturation when
the concentrations tested ranged from 1 to 100 mM (100-fold increase).
Absorption rates of cacodylic acid and other organic arsenicals did not appear
to be related to molecular size; therefore, it was unlikely that passage
through membrane pores was an important pathway.
Absorption reportedly takes place by diffusion through lipoid regions of
the intestinal boundary, a pathway reported to be utilized by a great many
drugs and other organic substances. This pathway was suggested because the
absorption process did not show evidence of saturation and the absorption rate
of the arsenicals ranked in the same order as the CHC13 to water partition
coefficients of the compounds. The absorption halftime (minutes) was 201 for
cacodylic acid.
Peoples (1971) reported on older pharmacological literature comparing
cacodylic acid and another arsenical as tonics, in which reference was made
to the disadvantage of .cacodylic acid, namely the foul odor of "cacodyl" on
the breath.
Peoples (1975) and Irgolic (1975) suggested that the odor of cacodyl
may have been confused with that of another arsenical. According to Doak
and Freedman (1971), cacodyl is too unstable in moist air and too toxic to
be the material detected. Peoples (1975) noted that since cacodylic acid
is still used as a popular tonic in some parts of Europe, there is a potential
data source for future study.
54
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Goodman and Gilman (1958) reported that sodium cacodylate is metabolized
to cacodyl oxide and inorganic arsenic. It is also possible that trimethy-
larsine (CtAs is one of the detected materials.
In the cow, excretion of cacodylic acid was found to occur primarily by
urine (75 to 80%) . A balance between intake and output was established after
30 days feeding at 24.5 mg/day (Peoples 1963).
The nonavailability to the rat of arsenic bound in swine liver was
demonstrated by Overby and Frost (1962). Three diets were used. The control
diet was prepared using acetone-dried liver powder. The tissue-arsenic diet
consisted of liver powder obtained from arsanilic-acid-f ed swine, and the
inorganic-arsenic diet consisted of control liver powder plus 3.3 mg of
As203/100 g.
The amounts of elemental arsenic contained in these diets were less than
0.1 ppm for the control, 6.0 ppm for the tissue arsenic, and 6.5 ppm for the
inorganic arsenic diet.
Rats were fed on the 3 (ad libitum) diets in a 7-day cycle. Feeding was
continued with some animals up to 42 days. The diets and daily feces and
urine collections were analyzed for total arsenic.
The metabolic inertness of liver-bound arsenic was demonstrated by the
fact that 97% of the "tissue arsenic was excreted during the feeding period
and the following 7-day control period. However, only about 50% of the inor-
ganic arsenic was excreted during the same period under the same test conditions.
The results of this investigation appear to parallel the results of an
earlier study (Coulson et al. 1935) in which "shrimp arsenic" was reported
to be retained by rats at much lower levels than was inorganic arsenic.
The strength of the tissue-arsenic bond is emphasized by the fact that
liver arsenic was not easily solubilized in vitro by the usual chemical or
biochemical digestion methods. Ashing was necessary to convert tissue arsenic
to a form that could be readily reduced and distilled as arsine.
Calesnick et al. (1966) demonstrated that when the tissues of chickens
which have been fed 7^As-labeled arsanilic acid were eaten by human volun-
teers, there was a rapid excretion of 7*As. Differences between urinary and
fecal recoveries of tissues 74As and pure ^As-labeled arsanilic acid were not
statistically significant. According to the authors, this suggests that the
arsenicals in tissues of chickens fed arsanilic acid is absorbed and excreted
in humans in much the same manner as is pure arsanilic acid.
The excretion and distribution of pentavalent and trivalent arsenicals
were studied in adult male albino rats. Nonfasted and 24-hr fasted animals
were given a single intravenous dose of one of the test materials. Urine
and bile collections were made for 1 hr, and then the liver, kidney, heart,
spleen, and RBC's were removed. Total arsenic was determined on these tissues.
55
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Twenty-one to 64% of the pentavalent arsenicals were excreted in the
urine; only 9 to 24% of one trivalent arsenical was excreted, and this
primarily in bile. Arsenite-injected rats had the highest arsenic accumulation
in the liver. The pentavalent arsenicals tended to accumulate to their higher
levels in the kidney. Differences in accumulation between trivalent arsenic
and pentavalent arsenic were not observed in heart, RBC's, and nonfasted spleen
(Schreiber and Brouwer 1964).
When arsenite was given as an intravenous injection to man, it was
recovered in the urine as a mixture of arsenite and arsenate with the latter
predominating. This suggested in vivo oxidation and preferential excretion
of arsenic in the urine as the arsenate (Mealey et al. 1959).
Tissue Accumulation - In cattle, the principal sites of storage of cacodylic
acid aYsenic were the liver, spleen, and pancreas. However, even in these
principal sites, the tissue"Tevels were low (Peoples 1963).
After 1 week of feeding on a cacodylate-free ration .following 10 weeks
feeding on diets containing the acid, tissue residues of ajrsenic in chickens
were found to have been reduced. Data from this test is shown in,Table 9-.
Ledet et al. (1973) found that arsenic levels decreased rapidly in the
organs and skeletal muscles of pigs after removal of the animals from a diet
containing arsanilic acid. This result indicated that irreversible accumula-
tion of organic arsenic in tissues does not occur. .. . , . .. .
Mutagenic Effects
Histidine-requiring mutants of Salmonella typhimurium;were used by several
investigators to test the mutagenic properties of cacodylic acid as well as
other herbicides. Cacodylic acid was evaluated by measuring its effect,on
bacterial genetics by the induction of reversion to histid^ne independence.
Test results indicated that cacodylic did not possess a mutagenic potential
in this system (Andersen et aL 1972).
56
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Table 9. ARSENIC IN TISSUES OF CHICKENS FED
CACODYLIC ACID (30 ppm)
Sample ppm in Tissues
interval Fat Liver Muscle Kidney
After 10 weeks
30 ppm dietary <0.05 0.23 0.23 0.23
10 weeks dietary at
30 ppm + 7 days
arsenic-free diet <0.05 <0.05 0.082 <0.05
Source: Bodden (1968).
Early studies reported a similarity in the mitotic effects of cacbdylic
acid and colchicine, a cytokinetic agent (Hartwell et al. 1946; King and
Ludford 1950;. Anso 1953). However, Salzgeber (1955) indicated that sodium
cacodylate is less cytoxic in its effects than colchicine.
Oncogenic Effects
Pathogen^free mice were used in studies aimed at determining tumorigenicity
by oral administration of cacodylic acid. A daily dosage of 46.4 mg/kg of
cacodylic acid was given in distilled water from 7 to 28 days. Thereafter,
the test material was incorporated in feed at a level of 121 ppm arid fed ad
libitum for nearly 18 months. The positive controls1 (7 tumorigenic compounds)
and the cacodylic-acid-treated groups were compared with the grouped negative
controls. Analyses were performed with 4 tumor groupings: hepatomas, pulmonary
tumors, lymphomas, and total mice with tumors. Fr'om these tests it was deter-
mined that eaeodylic acid did not cause a significant increase in tumors (Innes
et al. 1969).
A complete review of the relationship of oncogens in all arsenic compounds
is beyond the scope of this review.
Teratogenic Effects
A study of the teratogenic potential of cacodylic acid in the CD rat
and CD-I mouse is now in progress. Groups of rats and mice intubated with
cacodylic acid during the critical period of organogenesis will be evaluated
for. weight gain, liver/body weight ratio, percent mortality, number of insemi-
nations, number of term pregnancies and number of implantations. Litters from
these animals will be examined for defects and will be evaluated with respect
to percent mortality, body weight and lung/body weight ratio. (Chernoff 1975).
57
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References
Andersen, K. J., E. G. Leighty, and M. T. Takahashi, "Evaluation of Herbicides
for Possible Mutagenic Properties," J. Agr. Food Chem.. 20:649-656 (1972).
The Ansul Company, "Studies on the Toxicology of Ansar 560 in Dairy Calves,"
Submitted to Environmental Protection Agency (undated).
Ansano, T., "Effect of Cacodylic Acid Upon the Yoshida Sarcoma," J. Exptl.
Med. (Japan), 57:227-230 (1953).
Bodden, R. M. , "Toxicity of Cacodylic Acid to Animals," Wisconsin Alumni
Research Foundation, EPA Pesticide Petition No. OF0911 (1968).
Calesnick, B., A. Wase, and L. R. Overby, "Availability during Human
Consumption of the Arsenic in Tissues of Chicks Fed Arsanilic-7* as Acid,"
Toxicol. Appl. Pharmacol.. 9:27-30 (1966).
.-:,,•••" ' I)
Chernoff, N. (Experimental Biology Division, Office of Research and Development,
Environmental Protection Agency, Research Triangle Park, North Carolina), Per-
sonal communication regarding the teratology of cacodylic acid, to William Burnam,
Metabolic Effects Branch, Criteria and Evaluation Division, Office of Pesticide
Programs,'Environmental Protection Agency (November 24, 1975).
*
Coulson, E. J., R. E. Remington, and K. M. Lynch, "Metabolism in the Rat of
the Naturally Occurring Arsenic of Shrimp as Compared with Arsenic Trioxide,"
J. Nutrition. 10:255-270 (1935). ,
Derse, H., Report on;Ca^qdylic Acid Toxicity to Animals, Wisconsin Alumni
Research Association, EPA Pesticide Petition No. OF0911 (1968).
Doak, G. ;0., and L. D. Freedman, Organometallic Compounds, of As, Sb, and
Bl, Wiley, New York, jSqw York: (19 71).
Goodman, L. S., and A. Gilman, The Pharmacological Basis of Therapeutics,
2nd ed., MacMillan Co., New York, New York (1958).
Hartwell, J. L., M. G. Sheak, J. M. Johnson, and S. R. L. Kornberg, "Selection
and Synthesis of Organic Compounds," Proc- Amer. Assoc. Cancer Res., 6:489-
490 (1946).
Hwang, S. W., and L. S. Schanker, "Absorption of Organic Arsenical Compounds
from the Rat Small Intestine," Xenobiotica. 3:351-355 (1973).
Industrial Bio-Test Laboratories, "Acute Toxicity Studies with Bolls Eye,"
IBT No. 601-05911, Submitted to The Ansul Company, Marinette, Wisconsin,
EPA Pesticide Petition No. R0058981 (January 13, 1975).
58
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limes., J. R. M., B. M. Ulland, M. G. Valeric, L. Petrucelli, L. Fishbein,
G. R. Hart, A. J. Pallotta, R. R. Bates, H. L. Falk, J. J. Gart, M. Klein,
I. Mitchell, and J. Peters, "Bioassay of Pesticides and Industrial Chemicals
for Tumorigenicity in Mice: A Preliminary Note," J. Nat. Cancer Inst., 42:
1101-1114 (1969).
Irgolic, J. (Texas A & M University), Private communication to Chemistry
Branch, Criteria and Evaluation Division, EPA (April 26, 1975).
Jones, W. G., "Some Cases of Arsenical Poisoning," The Veterinary Record,
70(39):785 (1958). :I:
Kay, J. H., Report on Cacpdylic Acid Toxicity to Animals, Industrial Bio-Test
Laboratories, Northbrook, Illinois, EPA Pesticide Petition No. OF0911 (1*961').
King, H., and R. J. Ludford, "Relation between the Constitution of Arsenicals
and Their Action on Cell Division," J. Chem. Soc. 72:2086-2088 (1950).
Ledet, A. E., F. R. Duncan, W. B. Buck, and F. K. Ramsey, "Clinical, Toxicological,
and Pathological Aspects of Arsanilic A.cid Poisoning in Swine," Clin. Toxico 1.,
6:439-457 (1973). '
• i '
Mealey, J., Jr., G.L. Brownell, and W.E. Sweet, :'Radioarsenic in Plasma,
Urine, Normal Tissues, and Intracranial Neoplasms," ANA Arch. Neurol. :' '
Psychiat., 81:310-320 (1959).
T . ' '
Merck, Inc., The Merck Manual of Diagnosis and Therapy, C. E. Lyght, ed.,
Merck, Sharp, and Dohme Res. Lab. (1966),. ..
Munasingle, D. R., K. Rajasurlya, and P. N. Thenabadu, "Polyneuropathy Following
Acute Arsenic Poisoning," Ceylon Med. J., 86:85-89 (1969). •
Nees, P. 0., Report on Cacodylic Acid Toxicity to Animals, Wisconsin Alumni
Research Foundation, EPA Pesticide Petition No. OF0911 (I960).
Nees, P. 0., Report on iCacodylic Acid Toxicity to Animals, Wisconsin Alumni-
Research Foundation, EPA Pesticide Petition No. OF0911 (1963).
Nees, P. 0., Report on Cacodylic Acid Toxicity to Animals, Wisconsin Alumni
Research Association, EPA Pesticide Petition No. OF0911 (1968).
Overby, L. R., and D. V. Frost, "Nonavailability to the Rat of the Arsenic
in Tissues of Swine Fed Arsanilic Acid," Toxicol. Appl. Pharmacol., 4:38-
43 (1962). !
Palazzolo, R. J., Report on Cacodylic Acid Toxicity to Animals, Industrial Bio-
Test Laboratories, Northbrook, Illinois, EPA Pesticide Petition No. OF0911
(1965).
Peoples, S. A., "Health Aspects of Arsenic Herbicides," Proc. 23rd Calif. Weed
Conf.. pp. 115-116 (1971).
59
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Peoples, S. A., Toxicity of Cacodylic Acid to Animals, University of California,
School of Veterinary Science, EPA Pesticide Petition No. OF0911 (1963).
Peoples, S. A., Private communication to Chemistry Branch, Criteria and
Evaluation Division, EPA (April 21, 1975).
Salzgeber, B., "Observed Modification in the Genital Organs of the Explanted
Chicken Embryo in vitro, After Treatment by Different Teratogenic Substances,"
Comp. French So. Biol.. 149:190-192 (1955).
Schreiber, M., and E. A. Brouwer, "Metabolism and Toxicity of Arsenicals I.
Excretion and Distribution Patterns in Rats," Fedn. Amer. Soc. Exper. Biol.
Proc. 23(2):19 (1964).
Tarrant, R. F., and J. Allard, "Arsenic Levels in Urine of Forest Workers
Applying Silvicides," Arch. Environ. Health, 24:277-280 (1972).
U.S. Department of Agriculture, "Toxicity of 45 Organic Herbicides to Cattle,
Sheep, and Chickens," Production Research Report No. 137, Agricultural
Research Service, Beltsville, Maryland (1972). i
Wagner, S. L., and P. Weswig, "Arsenic in Blood and Urine of Forest Workers,"
Arch. Environ. Health, 28:77-79 (1974).
(." .
Weaver, A. D*, "Arsenic Poisoning in Cattle Following Pasture Contamination by
Drift of Spray," The Veterinary Record. 74(9):249-251 (1962).
60
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PART II. INITIAL SCIENTIFIC REVIEW
SUSPART C. FATE AND SIGNIFICANCE IN THE ENVIRONMENT
CONTENTS
Page
Effects on Aquatic Species 62
Fish and Amphibia 62
Laboratory Studies . . 62
Field Studies . ,62
Special Laboratory Studies . . . . 64
Lower Aquatic Organisms 65
Laboratory Studies 65
Field Studies .66
Effects on Wildlife 66
Laboratory Studies ..... 66
Field Studies 67
Effects on Beneficial Insects 69
Interactions with Lower Terrestrial Organisms 72
Residues in Soils 77
Laboratory and Field Studies 77
Monitoring Studies 81
Residues in Water 81
Residues in Air 82
Bioaccumulation, Biomagnification 85
Environmental Transport Mechanisms . 87
References 90
61
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This section contains data on the environmental effects of cacodylic acid
and other closely related arsenicals, including effects on aquatic species,
wildlife, and beneficial insects and interactions with lower terrestrial
organisms. Residues in soil, water and air are discussed. Data is also
included on bioaccumulation and biomagnification of cacodylic acid and on the
environmental transport mechanisms of arsenicals. This section summarizes
rather than interprets data reviewed.
Effects on Aquatic Species
Fish and Amphibia -
Laboratory Studies - In studies on bluegill sunf ish (Lepomis macrpchirus) ,
Hughes (1969) reported a commercial formulation that contained 23.4% cacodylic
acid (as well as surfactant)v-had a 96 hr TI^ of 80 ppm. Another formulation
containing sodium cacodylate, made up of 30% cacodylic acid equivalent (AE)
was reported to have a 96 hr TI^ of 750 ppm. / , _
In another study, Cope (1969) reported the 96 hr LC^Q of the commercial
herbicide Phytar (unknown percentage of cacodylic acid) to be 16 ppm for
bluegill.
McCann (1969) reported that no deaths had occurred in bluegill exposed
to Phytar (99.3% cacodylic acid) at 100 ppm AI within' 72 hr at 65 °F, although
all bluegills exposed to 22.6% cacodyiic acid at 210 ppm AI died Trithin the
test period (hr not specified).
The 24 hr TI^ of Phytar 560 (22.6% sodium cacodylate and 3.9% cacodylic
acid) for rainbow trout (Salmo gairdneri) was reported to be 145 ppm at 55°^.
The 48 hr TL^ was 130 ppm, and the 196 hr TLm was 96 ppm AI.
Woodward (1974) reported the 96 hr LC^Q of cacodylic acid to cutthroat
trout (Salmo clarki) and lake trout (Salvelinus namaycush) as between 10,000
and 100,000 ug/liter.
Miller and Lowe (1966) reported no effects to longnose killlf ish
(Fundulus similis) when exposed to 40.0 ppm AI of cacodylic acid for 48 hr.
Field Studies - Lehn et al. (1970) studied the effects of repeated
applications of cacodylic acid on the populations of fish in 3 freshwater
streams that drained an area in which the herbicide was applied. In July and
August, 1969, 2,085 gal of the cacodylic acid formulation "Military Defoliant
Blue" were sprayed on a 1 mi^ test area. The formulation contained 4.7%
cacodylic acid, 26.4% sodium cacodylate, 3.4% surfactant, 5.5% sodium
chloride, 59.5% water and 0.5% antifoam agent. One gallon of this formulation
contains approximately 3.1 Ib of cacodylic acid equivalent per gallon, or 15.4%
of elemental arsenic. The total quantity applied was equivalent to about 10 Ib
of cacodylic acid per acre.
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The test area is on the Eglin Reservation, approximately 2 miles north
of Choctawhatchee Bay in Walton County, Florida. The test area and the
surrounding range area had been mechanically cleared of almost all vegetation
prior to the test. The soil in the test area was of the Lakeland-Eustis-
Blanton Association, consisting of 90.1 to 93.1% sand, 2.8 to 4.3% silt,
3.6 to 5.6% clay, and 0.0 to 0.46% organic matter. The cation exchange
capacity was low, ranging from 0.69 to 1.19.
The cacodylic acid applications occurred during the period of heaviest
rainfall; July precipitation in the test area was 14.92 in, 10.40 in was
recorded for August. Total annual rainfall in 1969 was 59.9 in.
Six sampling stations were established on 3 freshwater streams which
drain the test area. Periodic counts of 20 different species of fish were
made at the sampling stations during 3 months preceding the applications
(10 counts), during the 2 months in which applications were made (4 counts)
and during 3 months following the applications (8 counts). Species diversity
was determined by an equation which expresses the relationship between the
number of species and the logarithm of the total number of individuals.
Changes in the proportions of any one species present at each station before
and after the spraying were also studied.
Seven species of fish were found at all 6 sampling stations, i.e., the
sailfin shiner (Notropis hypselopterus), the mosquitofish (Gambusia affinis),
the blackbanded darter (Percina nigrofasciata), the brown darter (Etheostoma
edwini), the spotted sunfish (Lepomis punctatus), the speckled madtom
(Noturus leptacanthus), and the pirate perch (Aphredoderus sayanus). When
all pre- and post-treatment counts at a'll sampling stations were compared, it
was found that the numbers of sailfin shiners decreased markedly in 8 instances,
The numbers of all other fish in this group showed marked increases when pre-
and post-exposure counts were compared. Mosquitofish increased in 7 observa-
tions, speckled madtom in 6 observations, spotted sunfish in 4 observations,
black-banded darters and pirate perch in 2 observations and brown darter in
1 instance.
Of the remaining 13 species of fish, the distribution was as follows:
1 American eel, Anguilla rostrata, was found at 4 of the 6 stations; 1 Southern
brook lamprey, Ichthyomyzon gagei, was found at 3 stations; 3 species (the weed
shiner, Notropis texanus; the redfin pickerel, Esox americanus; and the spotted
sucker, Minytrema melanops), were found at 2 stations each and 8 species were
found at only 1 station, (the chain pickerel Esox niger, the rock bass
Ambloplites rupestris, the black madtom Noturus funebris, the Okefenokee
pigmy sunfish.Elassoma okefenokee, the tadpole madtom Noturus gyrinus, the lake
chubsucker Erimyzon sucetta, the spotted bass Micropterus punctulatus and the
starhead topminnow Fundulus notti). There were no statistically significant
changes in the numbers of any of these 13 species when pre- and post-treatment
numbers were compared.
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Of the 6 sampling stations, one showed a slight decrease in diversity
of species, in a comparison of diversity indices before and after spraying.
The diversity indices for the other stations either remained constant or
increased after spraying.
Water and silt samples were taken from the 3 streams before, during
and after spraying and were found to contain arsenic concentrations of less
than 0.05 ppm, the lower detection limit of the analytical procedure
employed. The authors point out that these arsenic residue levels are
lower than background levels found in many aquatic organisms and systems,
as reported by other investigators. Since the arsenic levels found in the
water and silt were too low to have an immediate effect on fish, the authors
suggest that the decrease in the relative numbers of Notropis hypselopterus
found at one sampling station, and other variations in fish population levels
were probably due to 1 or more extraneous variables, rather than to the
cacodylic a:cid applications. '
Literature searches, contacts with basic producers of cacodylic acid and
contacts with 5 U.S. Department of the Interior and Environmental Protection
Agency laboratories known to be engaged in fish toxicity studies with
pesticides, failed to produce any further data or reports on the effects of
cacodylic acid on fish under field conditions.
\'
As with all pesticides having 24-hr LC^Q values for fish greater than
1.0 ppm, commercial labels of formulated pesticides containing cacodylic acid
as an active'ingredient do not carry any direct warnings regarding fish toxicity,
except for the general statement, "Do not contaminate waters used for domestic
consumption, or by animals, wildlife and aquatic'life or for irrigation purposes.1
Special Laboratory Studies - Oliver et al. (1966), in a field study of the effect
of cacodylic acid on specific floral ecotones, also described the direct effect
of cacbdyii'c acid on pond fauna in laboratory bioassays. The results were too
heterogeneous for a statistical evaluation-but the authors reported that1 the
48-hr LD5Qrs for Gambusia affinis (mosquitofish), Notropis maculatus (tailight
shiner), and Bufo terrestris tadpoles (Southern toad) approached 1000 ppm.
Over a 2-week period Micropterus salmoides (largemouth bass) were fed mosquito-
fish that had been previously exposed to 1000 ppm cacodylic acid for 24-hr.
There was no apparent effect on the bass. The authors noted that fauna would
not be directly affected by field concentrations of cacodylic acid. However,
damage to vegetation from the pesticide would indirectly affect the fauna,
especially.the highly specialized species which are unable to adapt to environ-
mental modification.
In another study, Rostand (1950) studied teratogenicity in the tadpoles
of the red frog (Rana temporaria) exposed to sodium cacodylate as well as
4 known teratogens. The tadpoles were exposed to 1/10,000 (100 ppm) sodium
cacodylate for 3 weeks at the age of one month, when the buds of posterior
members began to appear. No quantitative results were given other than that
10 to 25% of the 100 to 150 tadpoles in each test exhibited abnormalities.
64
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In sodium cacodylate the only abnormality observed was rigidity of
posterior appendages without structural anomalies.
Lower Aquatic Organisms -
Laboratory Studies - The toxicity of cacodylic acid to estuarine
animals was studied in 1966 at the then existing Gulf Breeze, Florida
biological laboratory of the U.S. Bureau of Commerical Fisheries (Miller
and Lowe, 1966). Test organisms were exposed for 24 or 48 hr to cacodylic
acid concentrations of 1.6 ppm in natural flowing seawater at a temperature
of 19°C, and a salinity of 24 to 28% (parts per thousand). There were no
effects from cacodylic acid or pink shrimp (Penaeus duorarum) after 48 hr
exposure, nor on the Eastern oyster (Crassostrea virginica) after 24 hr
exposure. Effectiveness (or lack thereof) on shrimp was determined by the
percent of the population exhibiting paralysis or loss of equilibrium, and
the effects on oysters by percent decrease in shell deposition.
Sanders (1970) studied the toxicity of a number of herbicides, including
cacodylic acid, to freshwater crustaceans. Cacodylic acid was one of several
herbicides that were not toxic to scud (Gannpftrus fasciatus) after 96 hr
exposure at a concentration of 100 ppm.
Cox and Alexander (1973a) investigated the production of trimethylarsine
gas from various arseniq compounds, including cacodylic acid, by 3 sewage
fungi isolated from raw sewage, i.e., Candida humicola, Gliocladium roseum
and Penicillium species. Aliquots of raw sewage were added to, culture media
and exposed to successively higher concentrations of cacodylic acid, ranging
from 100 to 2,000 yg/ml. The enrichment cultures obtained in this manner
were incubated for 1 month at room temperature, and the headspace gas of
each incubation bottle was then tested for the presence of trimethylarsine
gas by odor analysis and gas chromatography. In addition £o cacodylic acid,
3 other arsenic compounds were tested in the same manner,,each at pH 5, 6
and 7. The typical garlic odor of trimethylarsine was detected in cultures
containing cacodylic acid at all 3 pH levels.
The aforementioned 3 species pf fungi were isolated from these
cultures and tentatively identified. Each of these organisms was grown on
different media in the presence of the 4 different arsenic sources, including
cacodylic acid, to determine the extent of their ability to produce trimethyl-
arsine gas. Candida humicola produced trimethylarsine with all 4 arsenicals,
the greatest amounts (87 and 41 nmoles, respectively) with cacodylic acid at
pH 5 and 6. Gliocladium roseum produced 2,970 to 3,700 nmoles of trimethyl-
arsine with one arsenical with no appreciable effect of pH. By contrast,
this organism produced only 10 nmoles of trimethylarsine from cacodylic acid
under the same conditions at pH 5, 52 nmoles at pH 6 and 253 nmoles at pH 7.
The third organism, an unidentified species of Penicillium. also produced a
small amount of trimethylarsine gas with cacodylic acid.
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Based on their data, the authors suggest that acid conditions in
sewage might be conducive to trimethylarsine production by certain fungi
from several arsenic sources.
In further studies, Cox and Alexander (1973b) investigated some of
the variables affecting the formation of trimethylarsine from cacodylic acid
and several other arsenicals by Candida humicola. Phosphate inhibited the
formation of trimethylarsine gas by growing cultures of £. humicola from
other arsenicals, but not from cacodylic acid. Phosphite suppressed the
production of trimethylarsine by the fungus from one arsenical but not from
cacodylic acid. Cox and Alexander correlate these observations with the
report by Da Costa (1972), concluding that phosphate failed to reduce the
fungitoxicity of cacodylic acid to several fungi, while it did overcome the
fungitoxicity of other arsenicals. Cox and Alexander postulate that phosphate
may suppress gas evolution by blocking the conversion of the arsenicals to
trimethylarsine at a stage between the mono- and dimethylarsenic compounds.
Field Studies - In 'their studies on the effects of cacodylic acid
applications on 3 freshwater streams draining the target area, Lehn et al.
(1970) included observations on lower aquatic organisms.
On each sampling date at each sampling station, the population levels of
several benthic organisms, including crayfish (Orconectes species), dragonfly
naiad (Gomphus species), freshwater snail (Neritian species) and an unidentified
immature freshwater clam were monitored. Observations were also made to detect
possible morphological effects on eelgrass (Vallisneria americana), the only
species of vascular aquatic plants that was common to all sampling stations.
None of these organisms exhibited any gross changes in population levels; all
remained abundant throughout the study period.
Effects on Wildlife
Laboratory Studies - The only laboratory studies on the effect of cacodylic
acid on wildlife deal with its oral toxicity to 3 avian species and one species
of deer.
For 5 successive days, 10 bobwhite quail chicks (Colinus virginianus)
were fed a standard diet containing 5,000 ppm of a material that contained
29% sodium cacodylate and 5% cacodylic acid. Fifty were fed an untreated
diet (negative controls) and 50 chicks were fed a diet containing a chlori-
nated hydrocarbon (positve controls). A 9-day LC5Q value was calculated to
be in excess of 5,000 ppm cacodylate.
Abnormal behavior was not observed during the test nor were any signs
of systemic toxicity noted. Necropsy revealed no adverse gross pathology
(Industrial Bio-Test Laboratories, 1973a).
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The subacute toxicity of sodium cacodylate to mallard ducklings
(Anas platyrhynchos) was determined in an 8-day dietary test. The test
material was administered to 10 ducklings in a laboratory ration for 5 days
at a level of 5,000 ppm. Fifty untreated controls and 50 positive controls
were used for comparison. The LC^Q was calculated to be greater than 5,000
ppm.
No abnormal behavioral reactions or signs of systemic toxicity were
noted in the cacodylate-treated ducks. Necropsy did not reveal any gross
pathological lesions (Industrial Bio-Test Laboratories 1973b).
The LD5Q of Silvisar 510 (54.3% cacodylic acid) for mallard hens was
reported to be greater than 2,000 mg/kg by Tucker (1969). The LD5Q for chukar
partridges (Alectoris graeca) of mixed sex was reported as equal to or greater
than 2,000 mg/k,g (one died).
Signs of intoxication included regurgitation, polydipsia, ataxia and use
of wings to aid in movement.
Tucker (1969) reported that 320 mg/kg of Silvisar given via stomach tube
did not cause death of a 15-month-old mule deer doe (Odocoileus hemionus
hemionus). Signs of intoxication included slight ataxia and imbalance, slowness,
soft feces and anorexia; a weight loss was observed over a 19-day period.
Field Studies - Norris (1971) presented an interim report on comprehensive
cooperative studies on the fate and environmental impact of organic arsenical
herbicides in the forest environment. The studies were initiated following
the death of 8 range cattle in forest areas where organic arsenical herbicides,
including cacodylic acid, had been used. Arsenic residues had been found in
hair and tissues from 4 of the dead cattle.
Schroedel et al. (1971) studied the effects of several arsenical herbicides
on wildlife. Animals (numbers not specified) were trapped at various intervals
after use of arsenical .herbicides, including cacodylic acid, and arsenic
residues were determined in specific tissues, or in the whole body. More than
400 determinations of arsenic residues were made on samples collected from 3
treatment areas in western Washington and 4 areas in eastern Washington. Several
species of birds, mountain beaver and porcupines did not contain detectable
arsenic residues. A single deer which was recognized by applicators as a long-
time resident of one of the treated areas was also collected. Histopathological
examination of tissues from this animal showed no arsenic-induced lesions and
chemical analysis revealed no arsenic residues. Voles, shrews, mice and
chipmunks contained low levels of arsenic shortly after thinning with
arsenical herbicides began. About 50% of these animals had arsenic residues
ranging from 0.5 to 9.8 ppm between 2 and 30 days following treatment. Most of
the residues found were less than 5.0 ppm. Few animals (number not specified)
collected more than 30 days after treatment contained detectable residues.
Most ground squirrels that were collected contained arsenic residues, similar
to those found in voles, shrews, mice and chipmunks, but 1 squirrel, collected
1 day after treatment, contained arsenic residues ranging from 17 to 30 ppm in
various body, parts.
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A total of 11 dead snowshoe hares were found in one particular treatment
area near Colville, Washington, between June of 1970 and February of 1971.
High levels of arsenic in tissues from these hares indicated that arsenic
poisoning was the cause of death, although postmortem degeneration prevented
more detailed studies. Most of the dead hares were found within a few
hundred yards of "wash areas," i.e., locations where crews would dispose of
remaining herbicide at the end of the working day and where they washed their
equipment and hands. The normal procedure at the time was to empty the
remaining contents of "squirt cans" and all wash water on the ground. Severe
damage to vegetation at these sites suggested high concentrations of arseni-
cals. When this method of disposal of excess herbicide and wash water was
discontinued, no further mortality of hares was observed in this area.
Samples of soil, forest floor material and vegetation from the "wash areas"
contained high levels of arsenic.
Two hares were collected 2 and 42 days following treatment with
arsenical herbicides in anoth'er area in eastern Washington. They did not
contain detectable arsenic residues. Five other hares collected in western
Washington 232 days after treatment contained either extremely low or
undetectable residues of arsenic.
In comparison study, T'aycumber (1971) observed the exposure of cattle
which were grazing in areas treated with arsenical herbicides, including
cacodylic acid. Pre- and post-exposure samples of hair were collected from
37 head of adult cattle prazing in 1970 ir. a forest area treated with cacodylic
acid (Silvisar 510, 50% purity) which was also the same area where cattle
mortality had been observed in 1969. Comparable pre- and post-exposure samples
were collected from 28 other head of cattle which were grazed in another forest
area being thinned with another arsenical herbicide during the grazing season
when these studies were conducted C1970). There was a statistically significant
(at t^e 5% level) increase in arsenic concentrations between pre- and post-
exposure samples at both sites. There was no significant difference in arsenic
levels between the two sites in samples collected at a given time. No cattle
mortality was observed in either of the 2 test areas. The author emphasized
that the animals from whom these tissue samples were taken were grazed in an
area which had been suMected to chemical thinning with arsenicals during the
same prazinp season.
A report on the toxicolctgy of Silvisar*' 510 (cacodylic acid) tree killer
by the Ansul Company (1968) points out that, in commercial tree-thinning use,
about 4 g of the formulated product (containing 50% of cacodylic acid equivalent
per gal) will be used per tree. Assuming that all of the cacodylic acid enters
the foliage after treatment, a 150-lb animal would have to consume all of the
foliage of about 10 trees to begin showing toxic symptoms. Furthermore, the
animal would have to do this "in a relatively short time" (not further specified)
since cacodylic acid is quickly excreted and does not accumulate in body tissues.
It would be practically impossible, Ansul concluded, for any animal to consume
enough foliage, fruits or nuts to show any toxic symptoms.
A report by Martin and Nickerson (1973) on arsenic, mercury, lead and
cadmium residues in starlings is of marginal interest to the objectives of the
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present study. In 1971, the authors collected starlings (Sturnus vulgaris) at
50 sites throughout the continental United States and analyzed them for
residues of arsenic, mercury, lead and cadmium. Sampling sites were chosen to
reflect varying environmental conditions, representing broad geographic areas
and different degrees of human activity and related pollution sources. Each
sample consisted of a "pool" of 10 starlings which were frozen immediately
after collection and kept in frozen condition until analysis. After appropriate
digestion, arsenic residues were determined by atomic absorption spectrophoto-
metry. The minimum level of sensitivity for arsenic was 0.01 ppm. Residues
found were expressed in parts per million of whole body, wet weight.
The arsenic residues found were generally much lower than those of the
other 3 metals. Except for a sample from Michigan which contained 0.21 ppm of
arsenic, all remaining samples had arsenic residues of 0.04 ppm or less, with
no arsenic residues detected in 8 of the samples. The authors pointed out that
arsenic residues in urban soil samples have been reported as high as 74.5 ppm,
but that apparently this arsenic is either unavailable to the starlings, or is
ingested in a form which is not retained in the body by this species.
Data from controlled investigations on the toxicity of cacodylic acid to
laboratory animals indicates that the mammalian toxicity of this chemical is
relatively low. Few reports are available on the effects of cacodylic acid on
wildlife. The observations from the studies conducted in the Pacific Northwest
as summarized by Norris (1971) indicate that misuse of organic arsenical
herbicides or careless dumping of excess concentrates or spray mixtures must
be avoided.
Effects on Beneficial Insects
In toxicity tests on honeybees (Apis mellifera)^ Atkins et al. (1973)
summarized the effects of a large number of pesticides and other agricul-
tural chemicals. In a laboratory procedure which primarily measures a pesti-
cide's contact effect, pesticides are applied in dust form to groups of-25
bees per test level, with 3 replicates for each of 3 colonies for a total
of 9 replicates per test level. The procedure permits determination of an
LDijQ value for each pesticide in micrograms of chemical per bee. Cacodylic
acid is included in Group III as "Relatively nontoxic to honeybees."
Cacodylic acid produced 5.6% mortality of bees at the rate of 157.12 ug/bee
(by the authors' estimates equivalent to 152.12 Ib/acre) after exposure for
48 hr at 80°F and 65% relative humidity.
Moffett et al. (1972) studied the effects of cacodylic acid and several
other herbicides on honeybees. About 50 bees were collected by vacuum cleaner
from entrances of colonies in an experimental apiary and placed in individual
wire cages measuring about 2x2x6 in. The bees were brought into the
laboratory and fed 60% sucrose syrup and distilled water. The next day, dead
bees were removed, and the cages with the remaining live bees were sprayed
with cacodylic acid in aqueous solution at a rate equivalent to 4 Ib Al at
20 gal/acre. Dead bees were counted daily after spraying. Each treatment was
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replicated 5 tines, Cacodylic acid was highly toxic to the sprayed bees.
?ew bees sprayed with cacodvlic acid died on the first day, but mortality
reached almost 60% on the third day, and all bees were dead 10 days after
spraying.
Morton et al. (1972) and Morton and Moffett (1972) studied the toxicity
of herbicides, including cacodylic acid, when fed orally to honeybees.
Ten g (approximately 100 individuals) of newly-emerged honeybees were placed
in 2 x 6 x 6 in screened cages. All bees were less than 24 hr old at the
time they were placed in the cages. The test herbicides were fed to the
bees in 60% sucrose syrup at concentrations of 0, 10, 100 and 1,000 ppm
by weight. Cacodylic acid was "extremely toxic" at the 100 and 1,000 ppm
by weight concentrations. It was among the most toxic of all herbicides
tested, producing high bee mortality at all 3 concentrations. At the rate
of 10 ppm by weight, 50% of the test bees were killed in 4.1 days; at 100 ppm
by weight, the bees' halflife was 2.6 days; and at 1,000 ppm by weight, 2.1
days.
The findings of Moffett et al. (1972), Morton et al. (1972) and Morton
and Moffett (1972) regarding the bee toxicity of cacodylic acid appear to be
at variance with those of Atkins et al. (1973). However, Atkins et al. applied
the test pedticides to honeybees in dust form, whereas Moffett et al. (1972)
applied the herbicides orally in sucrose syrup- It appears that cacodylic
acid may be more toxic to honeybees in aqueous solution than in the form of
a dry dust applied topically.
Commercial labels of formulated pesticides containing cacodylic acid
(or its sodium salt) as an active ingredient are not required to contain
any statements regarding toxicity to bees. A number of authors have investi-
gated the effects of forest trees treated with cacodylic acid on bark beetles.
"While these insects are pests, rather than beneficial species, these observa-
tions are of some interest and will therefore be reviewed briefly.
Chansler and Pierce (1966) investigated the brood survival of 4 species
of bark Tjeetles (Dendroctonus adjunctus, Dendroctonus obesus, I)endroctonus
ponderosae, and Dendroctonus pseudotsugae) in trees injected with cacodylic
acid. Two different formulations containing cacodylic acid were employed.
Both were, injected undiluted into the sap stream of spruce and pine trees
around the full circumference o^ the tree, about 5 to 10 in above the ground.
Treatment was made soon after beetle attack. Three to 7 months, after treat-
ment, the number of live immature beetles in the treated trees was reduced
by 84 to 98% compared with untreated trees.
Stelzer (1970) found that the Arizona 5-spined engraver (Ips lecontei)
attacked ponderosa pine trees poisoned with a fast acting herbicide containing
cacodylic acid. The density of attack and the mortality of different stages
of the beetle varied with the time of the year the trees were treated. The
density of live brood was reduced by about 70% in trees treated from April
to July, as compared to untreated trees felled during the same period.
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Trees poisoned from late July through August attracted more attacks than
those treated at any other time of the year. Trees felled about 1 month
after treatment in July were most effective as toxic trap trees.
Puffam anr>. Yasinski (1971) studied the effects of cacodylic acid on
the spruce beetle (Dendroctonus rufipennis), the most serious pest of Engel-
mann spruce in the United States. Spruce trees were frilled by hand hatchet,
and cacodylic acid formulated as Silvisar 510 (containing 50%, or Ib/AI/gal)
was applied to the trough by plastic squeeze bottle at the rate of 1 ml of
formulation per inch of tree circumference. Some treated trees were felled
at intervals after treatment; some were left standing.
Buffam and Flake (1971) applied cacodylic acid in the form of the
Silvisar 510 formulation in the same manner (adding 1 ml of formulation per
inch of tree circumference to a horizontal frill made completely around the
tree by hand hatchet, using a plastic squeeze bottle) to pine trees that
were recently attacked by the roundheaded pine beetle (Dendroctonus adjunctus)
This method gave 100% reduction of the pine beetles; application of the
silvicide to power saw-frilled trees, while significantly effective, was
not nearly as effective as the hatchet method.
Buffam (1971) then undertook further studies to define the best method
of producing lethal trap trees. By varying the timing and the cacodylic
acid dosage rate, a combination was sought that would attract as many beetles
as untreated checks, but would be lethal to them. It x^as found that trees
frilled and treated in mid-June with one-half the concentration of Silvisar
510 used previously and felled 2 weeks later worked best as beetle traps.
These trees showed about the same attack density as untreated, felled trees.
Bark beetle broods survived in untreated trees, while they did not survivec
in the cacodylic acid-treated trees.
Frye and Wygant (1971) reported very similar results, using cacodylic
acid (undiluted Silvisar 510 formulation) in frill girdles of Engelmann
spruce against the spruce beetle (DendrQctonus rufipennis). They observed
that other bark beetles, including Ips pil'ffrons, Polygraphus rufipennis
and Scjerus annectens, were also killed by the treated trap trees. Striped
ambrosia beetles (Trypodendron lineatum) were attracted to the treated trees,
but their development was not adversely affected by the treatment.
Fewton and Holt (1971) reported on studies in which 60 yr-old "onderosa
nines were injected with cacodylic acid and a mixture of another arsenical
compound. Treatments consisted of cacodylic acid at 5.7 Ib/AI/gal* the
other compound at *.67 Ib/AI/gal; and a 50:50 mixture of the 2 solutions,
applied by infection with a Wypo-Hatchet tree iniector at waist height.
A volume of about 1.3 ml of undiluted material was applied in each injection.
The experiment included 1,080 trees, treated with the 3 herbicides at 3
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spacings on 6 treatment dates. In the treatment area, the presence of all
insects under observation was confirmed in scattered, dead or dying trees.
Plots thinned with other treatments which included felling and nonarsenical
injection were also in the vicinity. All organic arsenical treatments re-
sulted in lower attack levels on the treated trees than on the control
trees by the insects studied, including the mountain pine beetle (Dendroc-
tonus ponderosae) and the pine engraver (Ips pini). No larvae of these
species were found alive. There was much evidence of larval mortality and
hatch failure. The authors speculated that an endometatoxic reaction
involving reduction of the organic arsenicals to arsines may be a possible
explanation for the insecticidal effectiveness observed.
It is significant that the controls in the experiment consisted only of
untreated, felled trees. The authors failed to take into account in their
experimental design that these beetles preferentially attack dead, felled
trees even over dead, standing trees (Nagel et al. 1957).
Copony.and Morris (1972) combined the use of cacodylic acid (in the
form of Sivisar 510) with the use of bark beetle attractant to trap
emerging southern pine beetles (Dendroctonus frontalis) in a heavily
infested stand of pines in eastern Virginia. The attractant was successful
in luring^beetles to properly located trap trees. Cacodylic acid was used
at the average rate of 1.2 ml of the 50% formulation per in of tree diameter
applied, to a shallow frill girdling each tree. This treatment resulted in a
3.5-fold increase in aborted attacks and reduced the brood of successfully
attacking beetles by 59.9%.
Buffam et al... (1973) and Coulson et al. (1973) report on further
refinements of the "lethal trap tree technique" against the spruce beetle
(Dendrocjonus rufipennis), and the southern pine beetle (Dendroctonus fr-Qntalis)
Variables studied .included: the use of cacodylic acid at full strength and half
strength; comparison .of the treatment and felling of trap trees in the fall
(preferable from an operation standpoint) and the spring; the number of trees
treated with cacodylic acid.; ^and the number of trees baited with beetle
attractant. Buffam et al. (1973) analyzed phloem samples for arsenic and found
that arsenic applied by way of cacodylic acid was translocated in this tissue.
Check trees showed low levels, and treated trees generally higher, though
variable,: levels of arsenic. There was an inverse relationship between bark
beetle larval numbers and arsenic concentrations in the phloem of treated trees.
Interactions with Lower Terrestrial Organisms
Studies on the interactions between arsenicals and microorganisms date
back to the last century. Gosio, a nineteenth-century Italian scientist,
observed that certain fungi produce a poisonous gas from moldy wallpaper due
to arsenic in the pigment. In the subsequent literature, this gas became
known as "Goslo-gas."
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Challenger et al. (1933) and Challenger and Higginbottom (1935) identi-
fied "Gosio-gas" as trimethylarsine. They demonstrated that a strain of
Penicillium brevicaule added to culture media containing cacodylic acid
(free from inorganic arsenic) produced trimethylarsine. They conducted a
large number of experiments in an effort to elucidate the mechanism of this
biological methylation, but were unable to reach a definite conclusion. In
the course of these studies, they found that 3 bacterial species, Bacterium
mesentericus vulgatus, IJ. mensentericus ruber and JB. subtilis did not give
off the typical garlic odor of trimethylarsine when added to glucose-meat
extracts which contained various arsenicals.
More recently, McBride and Wolfe (1971) showed that cell extracts and
whole cells of a strain of Methanobacterium both methylate and reduce arsenate
to dimethylarsine under anaerobic conditions. These preparations produced
dimethylarsine from arsenate, arsenite and methylarsonic acid (MAA). The
process involves a series of methylations and reductions, and requires
adenosine triphosphate, hydrogen and a methyl donor (^C-labeled methyl-
cobolamin was used as methyl donor in these tests). In the pathway, arsenate
is reduced to arsenite which is methylated to form MAA. Dimethylarsinie acid
(cacodylic acid), formed by.the reductive methylation of MAA, is reduced to
dimethylarsine. The authors point out that pollution hazards exist when
arsenic and its derivatives are introduced into an environment where anaerobic
organisms are growing. They emphasize that the importance of organisms such
as Methanobacterium which convert toxic molecules to more toxic derivatives
should not be underestimated.
Newton (1971) also studied the microbial degradation of cacodylic acid
and other arsenicals. Media were prepared from Czapek-Dox agar with a range
of arsenical and glucose (as an energy source) concentrations, inoculated
with a mixture of mold organisms cultured from wood, incubated for various
periods of time, dried and analyzed by neutron activation. Each concentration
of each arsenical was tested at glucose concentrations of 0.3, 1.0, 3.0 and
10.0% by weight. Cacodylic acid concentrations studied were 0, 100, 1,000
and 10,000 ppm in terms of organic arsenic. Thus, there were 16 combinations
of arsenic and glucose for each herbicide studied. Each combination was re-
plicated 5 times.
Substantial losses of arsenic occurred at all levels of glucose, and
at all 3 concentrations of cacodylic acid tested. These arsenic losses
occurred through volatilization at temperatures below 70°C. The author con-
cluded that high concentrations of organic arsenicals are subject to attack by
molds and perhaps other microorganisms. Arsines, most likely trimethylarsine,
appear to be the principal metabolites responsible for escape of arsenic from
the cultures. The findings suggest, in the author's opinion, that there may
be substantial losses of arsenic through volatilization following application
of organic arsenical herbicides, and that the role of organic arsenical her-
bicides as persistent compounds needs to be reexamined.
A series of tests were conducted to determine if soil microorganisms
contributed to the degradation of cacodylic acid. The test herbicides were
added to soil samples collected in California, Alabama, the Central Plains of
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Texas and the Rio Grande Valley of Texas. Cacodylic acid (in the form of the
product Phytar 560) was added to the soil samples at a concentration of 50 ppm
of acid equivalent, or 27.6 ppm of elemental arsenic. One-half of the soil
samples were sterilized by autoclaving prior to addition of the herbicide.
All samples were again subdivided, and about 1 g of corn syrup was added to
one-half of the samples to evaluate the effects of an energy source. All
samples were exposed to sunshine. The weight of each sample was checked
periodically, and water was added to bring the sample back to its original
weight if a loss had occurred. Periodically, aliquots were analyzed for
arsenic residues and evaluated for the composition of the microbial population
present.
Isolations made from serial dilutions of soil samples indicated that there
was no apparent toxicity to soil microbes due to the presence of cacodylic acid.
Analysis of soil samples for elemental arsenic after 60 days showed considerable
variations. No conclusions could be drawn regarding the effects of the
microorganisms on cacodylic .acid (May 1974).
Zabel and O'Neil (1957) studied the toxicity of 44 arsenicals, including
cacodylic acid, to 4 common slime-forming organisms by a petri plate method.
Some of the more complex organic arsenicals demonstrated considerable bacteri-
cidal and fungicidal activity. Generally, there was no correlation between
toxicity to the microbes and the amount of arsenic in the molecule. Cacodylic
acid and most of its salts, with the exception of silver cacodylate and
8-hydroxyquinoline cacodylate, revealed very low activity; they showed no
slimicidal potential at concentrations of 2,000 ppm or above. Ineffective
salts included the copper, zinc, lead, bismuth, sodium, potassium, magnesium,
iron, calcium and barium cacodylates. Two bacteria and 2 fungi of importance
in slime formation were used as test organisms, i.e., Aerobacter aerognes,
Bacillus mycoides, Aspergillus niger and Penicillium expansum. Silver
cacodylate evidenced strong bactericidal and low fungicidal activity. This
difference was apparent in many arsenicals and suggests that there may be
basic metabolic differences in the handling of arsenic between fungi and
bacteria.
Malone (1971, 1972) investigated the effects of cacodylic acid applied
to a fescue meadow on soil microorganisms. Plots measuring 5 x 7 m were laid
out in a meadow composed of about 90% fescue, the remainder consisting of
approximately 30 different herbaceous species. Cacodylic acid was used in
the form of the commerical formulation Phytar 560, containg 22.6% sodium
cacodylate, 3.9% cacodylic acid and 73.5% of other ingredients, including
surfactants. In June of 1970, plots received single applications of the
herbicide at the rate of 9 and 27 Ib/acre of the commercial product. A
third treatment series consisted of 3 applications of 9 Ib/acre,-repeated
3 times at monthly intervals, fpr a total of 27 Ib/acre throughout the
growing season. Treatments and untreated controls were replicated 3 times.
The single applications at 9 and 27 Ib of product per acre reduced the
fescue biomass by 38 and 89%, respectively. The repeated applications
reduced fescue by 83%. Regrowth of vegetation began in August, and at
the end of September, most plots had recovered to near original levels of
fescue biomass.
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rhe responses of soil microorganisms to these treatments were evaluated
bi-weekly, beginning 1 week before the treatment date and continuing-^
throt^hout September. Four soil samples were obtained fr^tn .each plot,
combined and used to prepare serial dilutions for plates of bacteria and
fungi. The herbicide treatments increased the numbers of soil bacteria
and decreased the numbers of fungi, but both effects were of short duration
and did not persist throughout the growing season. It is not known whether
the increases in the numbers of soil bacteria were caused directly by the
herbicide, or secondarily by death of the vegetation. The results of
laboratory tests, which examined the direct responses of soil bacteria and
fungi to the herbicide, suggest that the herbicide affected the soil
microorganisms directly, rather than secondarily by death of the vegetation.
The results indicate, in the author's opinion, that the use of sodium
cacodylate for nonselective control of fescue meadow vegetation will have no
drastic effect on the gross numbers of soil bacteria and fungi, nor on the
decomposition processes in the soil.
Macklin and Witkamp (1973) studied the rate of decomposition of leaf
litter from tulip poplar trees defoliated with cacodylic acid at one-third,
1 and 3 times the normal rate of application used for crown-kill. Tulip
poplar trees with a diameter of 2.5 to 2.9 in at breast height (DBH) were
injected with a cacodylic acid formulation, Silvisar 510 (containing 50%
of AI), at the rate of 1 ml of formulation (equivalent to 0.719 g of cacodylic
acid) per 2-in DBH, and one-third and 3 times that rate. Leaf litter was col-
.lected from the treated and from comparable untreated trees and transported "
to an area of forest floor beneath a mature stand of second growth tulip pop-
lars away from the collection area. Data was collected weekly on carbon di-
oxide evolution, litter breakdown, and on densities of fungal mycelia and
invertebrate taxa associated with both the treated and untreated litter.
At the triple dose rate (2.517 g of cacodylic acid per 2-in DBH), there
was a significant reduction in carbon dioxide evolution from the forest
floor. At both the normal (0.719 g per 2-in DBH) and the triple rate,
densities of Entomobryidae (Collembola) increased significantly, while there
was a significant decrease in the densities of fungal mycelia. However, all
statistically significant effects were transitory. Over a 4-month period,
cacodylic acid had no overall effect on the microbial processes in the
study area, including decomposition processes and carbon dioxide evolution.
Bollen (1974) investigated the toxicity of cacodylic acid to microorganisms
in forest floor and soil. Six bacteria (Bacillus subtilis, Micrococcus
caseolyticus, Enterobacter aerogenes, Pseudomonas fluorescens, Streptomyces
antibioticus and Streptomyces olivaceus) and 4 fungi (Penicillium claviforme.
Pennicillium restriction, Aspergillus nidulans and Trichoderma viride) were
grown in pure culture on media to which cacodylic acid at concentrations of
0, 1, 10, 100, 1,000, or 10,000 ppm of arsenic had been added. The 2
Streptomyces species and the fungi were grown on plates which were incubated
at 28°C for 4 weeks, while the remaining 4 bacteria were grown in nutrient
broth cultures incubated at 28°C for 7 days.
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The effect of cacodylic acid on liquid or plate cultures resulted in a
slight reduction in growth of Bacillus subtilis and Micrococcus caseolyticus
at 1,000 ppm of arsenic.
In further tests, triplicate samples of soil and forest floor material were
treated with cacodylic acid at concentrations of 0, 10, 100 and 1,000 ppm of
arsenic. Treated samples were incubated in pint bottles at 28° C, and carbon
dioxide evolution was measured 7, 14, 21 and 28 days after treatment. The rate
of carbon dioxide evolution was much greater from forest floor material than
from soil. Cacodylic acid had no significant effect on the rate of carbon
dioxide evolution from soil. In forest floor material, the rate of carbon
dioxide evolution declined with increasing concentrations of cacodylic acid.
However, even at the highest rate tested (1,000 ppm of arsenic), the C02
evolution decreased by only 10 to 20%.
Bollen (1974) pointed out that in the use of cacodylic acid for pre-
commercial thinning in forests, concentrations of arsenic greater than 10 ppm
in forest floor and soLl will occur infrequently and will then usually be
restricted to only a few square feet, providing careful handling and appli-
cation techniques are used. He concluded that cacodylic acid will not
seriously affect forest microbial populations, their decomposition of
organic matter, or other functions important in the maintenance of soil
fertility.
Da Costa (1972) studied the toxicity of several arsenic compounds to
microorganisms as affected by phosphate. Fungi, including Pori monticola
and Cladosporium herbarum, were grown on solid nutrient media to which the
appropriate quantities of arsenicals and/or phosphates were added. One of
the arsenicals completely inhibited the growth of Pori monticola at a con-
centration of 0.0025 molar. The growth of £. herbarum was reduced by 36%
at 0.08 molar potassium arsenate. When increasing quantities of phosphate
in the form of lO^PC^ were added, the fungi were progressively less inhibited.
The addition of phosphate reduced the'fungitoxicity of arsenite in the same
manner, but not that of sodium cacodylate. The counteracting effects of
phosphate on arsenate toxicity occurred with every one of a wide variety of
microorganisms tested in the same manner. The author suggested that the
fungitoxicity of arsenate is due to its competitive interference with phos-
phorus in oxidative phosphorylation, rather than to a reaction with
sulfhydryl groups of proteins. He further suggested that the latter mechanism
is, however, probably operative with sodium cacodylate, which would explain the
fact that its fungitoxicity was not reduced by phosphate.
The data reviewed in this subsection indicates that cacodylic acid does
not adversely affect soil micoorganisms under field conditions, even at
concentrations much higher than those likely to result from commercial use
in accordance with label directions. Some microorganisms appear to be
capable of degrading cacodylic acid,»as well as other organic arsenicals. In
some studies (Malone 1971), cacodylic acid appeared to inhibit the growth of
fungi more than bacteria, whereas in others (Zabel and O'Neil 1957), cacodylic
acid and other organic arsenicals were more toxic to bacteria than to fungi.
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The findings of Da Costa (1972) suggest that the toxicity of cacodylic acid
to fungi may be due to reaction with sulfhydryl groups of essential proteins,
whereas the fungitoxicity of arsenates and arsenites seems to be due to the
competitive interference of arsenic with phosphorus in oxidative phosphory-
lation.
Residues in Soil
Laboratory and Field Studies - The degradation of organoarsenicals in the soil
is a complex chain of events. Complete degradation would involve mineralization
of the herbicide molecule (Woolson 1974). Arsenic compounds are normal soil
components; they contribute about 4 ppm of arsenic (dry weight) to most plants.
Consequently, most plants are not adversely affected until high arsenic
concentrations are reached in soils. For instance, Woolson et al. (1970 a, 1973)
reported that arsenic concentrations in the upper 6 in of the soil of about
250 ppm reduced the growth of 4-week-old corn by approximately 50%. Under
these conditions, dry plant material contained about 10 ppm arsenic (dry
weight). Generally, according to Woolson et al. (1970a), the arsenic level
required for phytotoxicity is variable, and is influenced by the chemical form
and water solubility of the arsenic residues; soil fertility and PH; iron,
calcium, aluminum and phosphorus present; plant vigor; and other factors.
The organic portion of organoarsenicals can be metabolized. Metabolism
may include reduction to a volatile compound which may escape to the air
(Woolson 1974).
According to Woolson (1974), the degradation of cacodylic acid in soil
has not been extensively investigated. Woolson and Kearney (1973) studied the
persistence and reactions of 1<4C-labeled cacodylic acid in soils, with special
emphasis on the chemical distribution of cacodylic acid into water-soluble
iron, aluminum and calcium fractions in different soils under aerobic and
anaerobic conditions. Three soils (Lakeland loamy sand, Hagerstown silty clay
loam and Christiana clay loam) were treated with radiolabeled cacodylic acid
at 1, 10 and 100 ppm in 50-ml covered beakers. There were 3 replicates
per treatment. The soils were brought to 75% of field capacity and incubated
at 25° C for 32 weeks. Grab samples were taken periodically and analyzed for
the chemical distribution of cacodylic acid, for total arsenic, and for total
•*"^C content. The concentration of cacodylic acid was highest in the water-
soluble fraction, followed in decreasing order by the aluminum, iron and
calcium fractions. By contrast, inorganic pentavalent arsenic was largely
present in the iron and aluminum fractions.
The persistence of cacodylic acid was a function of soil type. After
32 weeks, the following amounts of -^C were recovered from the 3 study soils
by combustion: Lakeland, 62%; Hagerstown, 53%; and Christiana, 23%. The
rate of application had no appreciable effect on the disappearance of cacodylic
acid. Since the total C- cacodylic acid content generally paralleled a
disappearance of water-soluble cacodylic acid, the rate of degradation
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appeared to be a function of the concentration of water-soluble cacodylic acid
and, consequently, of the amount of cacodylic acid available for microbial
action. The results also indicate that cacodylic acid is not bound as readily
in the soil as inorganic arsenic and is therefore more likely to be leached.
Total l^c as well as total arsenic decreased in all soils with time. A
pungent garlic odor was detected in soils treated at the highest rate,
suggesting the evolution of a volatile alkylarsine.
The authors conclude that the degradation of cacodylic acid in soils
proceeds by 2 mechanisms. Under anaerobic conditions, 61% of the applied
cacodylic acid was converted to a volatile organoarsenical within a 24-week
period and was lost from the soil system. Under aerobic conditions, 35% was
converted to a volatile organoarsenical compound. In addition, the carbon-
arsenic bond cleaved, yielding C02 and AsO^-. The volatile organoarsenical
derivative may be dimethylarsine, an extremely unstable compound that may be
oxidized by air to the oxide or back to cacodylic acid and returned to the
earth by fixation to plants or soils. Dimethylarsine may also be oxidized
by rainfall. The ultimate environmental fate of the arsenic from cacodylic
acid, according to Woolson and Kearney (1973), appears to be metabolism to in-
organic arsenate which is bound in the soil in an insoluble form.
Ehman (1963b) studied the movement of cacodylic acid in treated soils.
Samples of pasture sod 10-in thick were obtained from fields of clay, silt-loam,
and sand. The samples were placed into 6 specially-constructed wooden boxes.
Three boxes were lined with polyethyline and equipped with holes and drains at
the bottom for collection of seepage samples. For several weeks, the samples
were watered lightly and allowed to acclimate to artificial indoor lighting
conditions. The 6 boxes were then each sprayed with cacodylic acid at a rate
equivalent to 15 Ib/AI/acre. Twelve hours after treatment, each of the boxes
equipped for collection of seepage was watered with the equivalent of 1/2 in
of rainfall. Subsequent waterings were at 1, 2 and 4 weeks. Twenty-four hours
after each watering, soil samples were taken from the first and second 3 in and
from the bottom 4 in of each type of sod. The soil samples were air-dried and
analyzed for arsenic content. Seepage samples were also analyzed for arsenic,
as well as for basicity or acidity.
The results indicated that after 4 weeks, essentially all of the arsenic
added to each of the 3 soils in the form of cacodylic acid remained in the soil.
Analysis of the seepage samples indicated that some leaching occurred in the
first 24 hr after treatment. After that, all samples showed a very low leaching-
of arsenic in all soil types. The author concluded that cacodylic acid is quite
strongly bound by all. 3 soil types; that a small but steady leaching of
cacodylic acid occurred in the watered soil; and that cacodylic acid,
applied to a sod surface, distributed rather evenly in about 1 week to a
depth of 10 in.
In a companion study, Ehman (1963a) observed the residual effects of
cacodylic acid on 7 crops, including snap beans, potatoes, sweet potatoes,
carrots, Chinese cabbage, field corn and soybeans. Field plots were laid
out, fertilized and sprayed with a cacodylic acid formulation (Ansar 138,
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containing 65% cacodylic acid) at a rate equivalent to 5 Ib/acre of cacodylic
acid. One-half of the plots were sprinkled with the equivalent of 1/2 in of
rain 24 hr after treatment. Plots were then planted with 2 20-ft rows of
each of the 7 study crops. Composite soil samples collected just before
treatment showed an average arsenic content of 3.68 ppm. The average of all
untreated samples was 3.98 ppm of arsenic. The cacodylic acid treatment
resulted in an average increase in the soil arsenic content of 3 ppm at the
3-in depth. There was no significant uptake of arsenic by edible parts of
the crops in the treated plots. Some elevated levels of arsenic were found
in leaves and stems of snap beans. The watering just after treatment had no
effect on the arsenic content of the soil samples.
In a similar study (Ehman 1964), alfalfa and ryegrass were planted on
pastureland treated with cacodylic acid (Ansar 138 formulation) at a rate
equivalent to 5 Ib/AI/acre 3 days prior to planting. Two of the 4 treated
plots were watered with the equivalent of 1/2 in of rainfall prior to planting.
Composite samples of the first cutting of alfalfa and ryegrass, and pre- and
post-treatment soil samples were analyzed for arsenic content. The arsenic
content of the soil samples increased by about 3 ppm, but there was no uptake
of arsenic by the 2 crops.
The effects of 6 annual applications of cacodylic acid on arsenic residues
in soil have also been studied. Cacodylic acid (Phytar 560 formulation) was
applied near Weslaco, Texas, for 6 consecutive years at the rates of 2.5 and
7.5 Ib/AI/acre/yr. Soil cores were collected at the end of each growing season
at 3 different depths ranging from 0 to 18 in. After 6 annual applications,
both rates of cacodylic acid resulted in a statistically significant build-up
of arsenic in the upper 6 in of soil (2.4 to 4.5 ppm arsenic above an average
background of 11 ppm). Arsenic residues in the 6- to 12-in soil layer were
increased only by the higher rate of cacodylic acid, and the arsenic residue
levels at the depth of 12 to 18 in were not affected significantly by any of
the cacodylic acid treatments.
During the 6-yr study period, a total of 8.1 and 24.0 Ib of elemental
arsenic were applied in the form of cacodylic acid at the 2 treatment levels.
These figures were converted to parts per million of arsenic in the soil and
added to the measured average background arsenic levels to arrive at the
theoretical level of arsenic that would be expected in the soil after the 6
annual treatments. For the 2.5 Ib/acre cacodylic acid rate, the total added
arsenic was 4.1 ppm. When added to the 11.0 ppm background, the total arsenic
level should have equalled 15.1 ppm; 13.4 ppm of arsenic were actually found.
For the 7.5 Ib/acre cacodylic acid treatment series, the calculated level of
arsenic when added to 11.0 ppm background was 12.2 ppm. The total arsenic
level should have equalled 23.2 ppm; 18.1 ppm of arsenic were actually^ound,
a deficit equivalent to 28.17% of the predicted concentration.
Speculating about possible reasons for these deficits, the investigators
reject leaching losses because throughout the entire 6-yr test period there
was no significant accumulation of arsenic residues in the 12- to 18-in soil
horizon. Microbial reduction of organic arsenicals to gaseous methylarsines
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appears to be a more plausible loss mechanism. The investigators further
suggest that the rate of reduction depends on the amount of organic
arsenicals applied to the soil. The amount of arsenic "lost" from the soil
in this study was proportional to the amount of organic arsenic added. Less
than 1% of the added organic arsenic was not recovered at the lowest rate of
application, while at the highest rate of application, 28% of the applied
arsenic was not recoverable in plots treated with cacodylic acid at 7.5 Ib
Al/acre. The 2 intermediate organic arsenic application rates resulted in
intermediate percentages of arsenic not accounted for.
If their assumptions are correct, the investigators hypothesize that
an equilibrium may eventually be reached in which loss mechanisms would
remove arsenic from the soil at the same rate as it is applied.
The treatment rates of cacodylic acid selected for this study are
equivalent to the recommended single treatment dose and 3 times the recom-
mended single treatment dose. The low rate of cacodylic acid corresponds
to the normal amount of this chemical that could be applied once during a
growing, season; the high rate corresponds to the cumulative seasonal dose
of 3 separate applications (Sandberg et al. 1973).
In the studies by Woolson and Kearney (1973), rates of application of
cacodylic acid ranging from 1 to 100 ppm had no appreciable effect on its
disappearance from 3 different soils. This observation would not support the
hypotheses of Sandberg et al. (1973). However, the rate of degradation or
disappearance of cacodylic acid varied considerably with different soil types
in the test by Woolson and Kearney (1973). Furthermore, their studies were
conducted under laboratory conditions over a time span of only 32 weeks,
while the studies by Sandberg et al. were conducted in the field and extended
over a period of 6 yr.
In an earlier study (Ehman 1967), plots of loamy fine sand in Fairfax,
South Carolina, were sprayed with cacodylic acid (Phytar 138 formulation) at
50 Ib/AI/acre. Three rates of another arsenical compound were studied
comparatively (15, 50 and 100 Ib/AI/acre).
On the day of treatment, cotton, soybeans, sorghum and peanuts were
planted in these plots. The initial peanuts had to be replanted 1 month
later because of excessive stunting of the first crop, especially in the
cacodylic acid-treated plots. Four weeks after planting, cotton, soybeans
and sorghum were also severely stunted in the cacodylic acid-treated plots.
Bight weeks after planting, the 3 crops were still somewhat stunted in the
cacodylic acid plots. The replanted peanuts were again somewhat stunted, but
not as severely as the first crop. All crops were harvested at the appropriate
times inj^he fall, and samples were analyzed. The same plots, without
retreatment, were planted with cotton, soybeans, grain sorghum, peanuts, oats,
corn, and tobacco the following year. There were no apparent adverse effects on
these crops from the cacodylic acid treatment applied the previous year.
Cottonseed, soybeans, sorghum grain and corn samples from the treated plots
showed somewhat higher arsenic residues each year as compared to untreated
control samples, with some reduction as time passed (Ehman 1967).
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In summary, the reports reviewed in this subsection indicate that
herbicidally effective concentrations of Cacodylic acid "disappear" rapidly
from soils under field conditions. Microbial degradation appears to contribute
partially to this loss. Several different chemical reactions seem to be
involved. According to Woolson (1974), cacodylic acid in the soil may undergo
a number of different chemical and biological transformations, including
formation of insoluble and biologically inactive arsenical salts; binding to
soil-arsenic complexes by adsorption or ion exchange; oxidative demethylation
to inorganic ortho arsenic acid; reduction to biologically active arsines; and
reductive methylation to biologically active methylarsines.
Monitoring Studies - In the National Soils Monitoring program for pesticides
(Stevens et al. 1970; Wiersma et al. 1971, 1972a, 1972b; and Carey et al. 1973),
arsenic residues have almost never been found in the samples of cropland,
noncropland and urban soils which were collected and analyzed. In general,
it is believed that most of these arsenic residues come from natural sources;
little or no correlation was found between high soil residue levels of
arsenic and the geographical use patterns of organic arsenical herbicides,
or of inorganic arsenical pesticides.
Cacodylic acid accounts for only a very small fraction of the total
quantity of arsenic applied in various forms and formulations for pesticidal
purposes in the United States. In view of the apparent lack of correlation
between environmental arsenic levels found in monitoring studies and the use
patterns of major arsenical pesticides, an attempt to correlate arsenic
monitoring data with cacodylic acid use does not appear to be promising.
Residues in Water
Cohan (1971) studied the arsenic content in irrigation water following
ditchbank application of cacodylic acid (sodium salt) to watered canals on
the T>io Grande, Texas, project of the Bureau of Reclamation. One canal, 2.1
miles in length, was treated with cacodylic acid at the rate of 5 Ib/acre.
The spray rig moved downstream while applying the herbicide to both banks and
the complete water surface. This is not the normal method for herbicide
application to a ditchbank, but represents the maximum concentration of
herbicide that could occur under similar operating conditions. The highest
arsenic concentration found in the water in this canal was 0.86 ppm 10 min
after spraying. The arsenic concentration declined rapidly thereafter and
dropped to below 0.1 ppm within 110 min after spraying.
Two other canals, 2.25 and 2.2 miles in length, respectively, were
treated at the same rate (5 Ib/acre) . The spray rig moved downstream spray-
ing one bank, then turned around and, traveling upstream, sprayed the other
bank. This represents normal herbicide application procedure. The maximum
arsenic concentrations found were 0.16 ppm in one canal 5 min after spraying,
and 0.17 ppm in the second canal 70 min after spraying. The arsenic concen-
tration persisted only for short periods of time.
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The arsenic concentration dropped to less than 0.1 ppm within 15 min after
spraying the first canal, and within 100 min after spraying in the second
canal.
Cohan's report does not analyze residues from canal bottoms or the effect
on plants along the edge of the canal. There is no mention of possible effects
on animals in and along the canals.
Lehn et al. (1970) studied the effects of aerial applications of cacodylic
acid to a test area on 3 freshwater streams draining the test area. The
experimental design and other study parameters employed by these authors are
described in the subsection on Aquatic Effects. Lehn et al. reported that
water and silt samples were taken from the 3 streams before, during, and after
the spraying of cacodylic acid. The limit of sensitivity of the analytical
method employed was 0.05 ppm. No detectable arsenic residues were found in any
of the water or silt samples analyzed in this program. The authors pointed out
that these levels are lower "than background levels of arsenic in other aquatic
systems and concluded that there was no appreciable migration of arsenic
residues from the test area to any of the 3 streams draining it.
Braman and Foreback (1973) analyzed environmental samples, including
samples of water from several rivers, ponds, and lakes, for arsenate and arse-
nite ions and methylarsenic acids in nanogram amounts. Dimethylarsinic acid
(cacodylic acid) residues ranging from less than 0.002 to 0.6 parts per billion
(ppb) were found in 7 natural waters (fresh waters) collected in and around
Tampa, Florida. In 3 samples of saline waters, dimethylarsenic acid concentra-
tions found ranged from 0.2 to 1.0 ppb. All of these samples also contained
small, varying amounts of MAA, and of trivalent and pentavalent arsenic. The
authors pointed out that dimethylarsinic acid is a major and ubiquitous form
of arsenic in the environment, and that it is particularly involved in biological
systems. MAA was generally, found in smaller concentrations than dimethylarsinic
acid, probably because it is only an intermediate in the the arsenic methylation
sequence. Dimethylarsinic acid is very resistant to oxidation and could have
considerable residence time in natural waters, unless subject to bacterial
oxidation.
Woolson (1974) states that the organic arsenical herbicides, including
cacodylic acid, are relatively nontoxic to fish and that, in addition, the
movement of these compounds from treated areas to water containing fish is
likely to be minimal because of fixation phenomena in plants, soils, and
sediments.
Residues in Air
Some investigators have suggested that organic arsenicals, including
cacodylic acid, may be reduced and methylated to form volatile, biologically
active methylarsines which escape to the air from treated areas. No data
was found on the possible presence and fate of such degradation products of
cacodylic acid (or of other organoarsenicals) in air.
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The Ansul Company pointed out that cacodylic acid has an extremely low
vapor pressure so there is no possibility of movement in air by volatilization.
There is some evidence of microbiological reduction and methylation of these
organic arsenicals to trimethylarsine. The Ansul Company believes that this
degradation is of a low order of magnitude since trimethylarsine is rapidly
oxidized in air to a nonvolatile, pentavalent arsenical. Trimethylarsine is
spontaneously inflammable in air, in contrast to the relative stability of
dimethyImercury in air.
Newton (1971), based on his studies reviewed in the subsection on "Inter-
actions with Lower Terrestrial Organisms," concluded that high concentrations
of organic arsenicals are susceptible to attack by molds, and perhaps other
microorganisms. Newton supported his conclusion by citing an experimental
procedure where significant amounts of arsenic were lost with no possible
opportunity for loss. He interpreted this as conclusive evidence of loss by
volatilization. Because the boiling points of the organic arsines are 52.7°C
(for trimethylarsine) or lower (Lange 1956), and because the other volatile
arsenic compounds implicated (cacodyl and cacodyl oxide) have boiling points
ranging above 150°C (Lange 1956), the conclusion is drawn that the arsines are
the principal metabolite responsible for escape of arsenic from these cultures.
The work of Challenger (1951) also supports this assumption that trimethylarsine
constitutes an important fraction of the lost arsenic.
The work reported here, together with conclusions drawn by Challenger (1951),
Newton and Holt (1971) and others, suggests that there may be substantial losses
of arsenic through volatilization after application of organic arsenical
herbicides. Because of this phenomenon, the role of the organic arsenical
herbicides as persistent compounds needs to be reexamined.
Ehman (1963c) reported on the toxicity of smoke and vapors from burning
grass previously treated with cacodylic acid. Plots were laid out in a field of
good pasture grass in August of 1963. One plot was treated at the rate of 5
Ib/acre of Ansar 138, a formulation containing 65% cacodylic acid; another plot
was treated at the rate of 15 Ib of cacodylic acid formulation per acre, and a
third plot was left untreated. Five days after treatment, the grass in the
treated plots was cut, and samples from all 3 plots were analyzed. The arsenic
content of the 3 dried grass samples was as follows: untreated, 0.3 ppm;
5 Ib/acre, 134 ppm; and 15 Ib/acre, 197 ppm. After each grass sample was burned
for the production of smoke, the ash was analyzed and found to contain 25 ppm
arsenic following the 5 Ib/acre treatment, and 96 ppm following the 15 Ib/acre
treatment.
Three groups of 10 albino rats each were then exposed to smoke produced
by burning 3 of the grass samples in a series of tests. Three grams of grass
was burned in a "bee smoker," and the smoke was pumped into a closed chamber
(6 cu ft) containing the rats. The animals were subjected to the smoke for 15
min, and the chamber was opened for a 15-min ventilation period. This cycle,
30 min in length, was repeated 10 times, and a total of 30 g of one of the 3
grass samples was burned for each group of 10 rats. After the tenth exposure,
5 rats were sacrificed, and their lungs were removed for histological exami-
nation. Five untreated animals (not exposed to any grass smokes) were also
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sacrificed as negative controls. The remaining test animals, 5 from each of
the 3 grass smoke exposures, and 5 negative control animals were observed for
a 2-week period. At the end of the period all surviving animals were
sacrificed and lung tissues were collected and examined histologically.
All animals exposed to the smoke and vapors from the burning grasses
showed signs of discomfort during the exposure periods, without significant
differences between samples. The animals held over for observation were sick
and gasped. Mortality was as follows:
Negative control No deaths
Untreated grass 2 deaths at 10 days, 1 death at 12 days
5 Ib/acre grass 1 death at 5 days, 1 death at 7 days
15 Ib/acre grass 2 deaths at 1 day, 1 death at 4 days
Clinical observations of the animals during the 2-week post-exposure
period did not show any marked variations between the positive control and
test groups. Histological examination showed more acute degeneration of the
bronchial epithelium in animals exposed to smoke from the grass treated at the
highest rates, as compared to the animals exposed to the grass treated at the
lower rate, or the untreated grass. This may indicate an increased irritation
and inflammation of mucous membranes from smoke produced by burning grass
treated with high rates of cacodylic acid.
In a second smoke inhalation study, the same test methods were employed,
except that only 2 g of grass were used per exposure, in contrast to 3
g/exposure used in the first study. In the second study, no animals were
sacrificed at the end of the exposure period, but all were observed for 14
days following exposure.
Some signs of irritation were again noted in all animals exposed to the
smoke from burning the grass samples. Only animals exposed to smoke from the
grass treated at 15 Ib of cacodylic acid formulation per acre exhibited labored
breathing after the 10 exposures, and one animal in this group died 4 days
later. Histological examination showed an increased peribronchial lymphoid
infiltration in tissue from the animals exposed to the smoke from burning the
grass treated at the highest rate.
Ehman (1963d) also studied the toxicity to plant life of smoke from
burning grass previously treated with cacodylic acid. Potted lima bean, corn,
cotton, and wheat seedling plants were placed in a 6 cu ft chamber and exposed
to smoke from a 3 g sample of pasture grass that had previously been treated
with 15 Ib/acre of Arrsar 138, a formulation containing 65% cacodylic acid.
After 20 min, 2 plants of each variety were removed from the chamber. The
remaining plants were exposed to 2 additional grass-burning cycles. Two more
plants were removed after each cycle. All plants were held for 1 week after
exposure, at which time phytotoxicity was recorded. Beans exposed to the
smoke of treated grass showed slight to severe damage; beans exposed to the
smoke of untreated grass showed slight to moderate damage. Corn, cotton, and
wheat showed no injury from exposure to the smoke of either treated or un-
treated grass.
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Bioaccumulation, Biomagnification
Isensee et al. (1973) studied the distribution of 1^C-labeled cacodylic
acid and dimethylarsine among aquatic organisms in a model ecosystem including
mosquitofish (Gambusia affinis), Daphnia magna, Physa snails, and algae (Oedo-
gonium cardiacum). The ecosystems were set up in glass aquariums 25.4 x 5.2 x
17.8 cm in size, each filled with 4 liters of "standard reference water" modi-
fied by increasing the NH^NOj and ^HPO^ concentration 5-fold to obtain satis-
factory growth of algae. The tanks were kept in the greenhouse in a shallow
water bath maintained at 22 + 1°C. Ten snails, a few strands of algae, about
30 daphnids, and a few milliliters of water from a previously set up aquarium
(containing various diatoms, protozoa, and rotifers) were added to each tank.
Five days later, duplicate tanks were treated with ^C-labeled cacodylic acid
at the rate of about 11.5 ppb added directly to the solution. After 29 days ex-
posure to cacodylic acid, samples of daphnids were taken from each tank, and 2
fish were added. The experiment was terminated 3 days later since the fish had
consumed all remaining Daphnia. Fish, daphnids, snails, and algae were thus ex-
posed for 3, 29, 32, and 32 days, respectively. All organisms in both control
and treated tanks prospered during the test period, indicating that the rate of
cacodylic acid used was not toxic.
The concentration of cacodylic acid in the solution 24 hr after it was
added was 10.6 ppb, based on radioactivity of the parent compound, equivalent
to 92% of the original radioactivity placed in solution. The authors attri-
buted the 8% loss of cacodylic acid radioactivity to initial absorption to al-
gae or other organisms. After 32 days, the solution concentration of cacodylic
acid had decreased to 6.1 ppb, a loss of 42% of the initial radioactivity meas-
ured at 24 hr. Seventy percent of this loss activity was accounted for in the
biomass (sum of living and dead organic material). Algae accounted for 74% of
the total biomass by weight, 95% of the radioactivity contained in the biomass,
and 28% of the activity added at the beginning of the experiment. Thus, in this
system, algae were the primary sink in which cacodylic acid residues accumulated.
Algae and daphnids bioaccumulated more cacodylic acid than did the 2 higher food
chain organisms (snails and fish), indicating that cacodylic acid did not bio-
magnify between food chain organisms.
Isensee et al. (1973) studied -^C-labeled dimethylarsine in a parallel test
series under the same experimental conditions. The rate of disappearance of the
radioactivity introduced into the system by dimethylarsine and its accumulation
in each organism were so similar to the behavior of cacodylic acid as to raise
the question of compound identity. The tanks were aerated, providing oxidizing
conditions that might convert dimethylarsine to cacodylic acid. To test this
hypothesis, snail extracts were analyzed by thin layer chromatography. Radio-
autographs from both compounds had similar Rf values, but differed sufficiently
with respect to tailing and ratios of mobile and nonmobile activity to indicate
that several different chemical species were present.
A second experiment of shorter duration was performed to determine the
relative importance of uptake from solution versus ingestion of one food chain
organism by another in the distribution of cacodylic acid among food chain
elements. Solutions containing 0.1, 1.0, and 10.0 ppm radiolabeled cacodylic
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acid were prepared, and about 500 mg algae and 300 Daphnia were exposed to
these concentrations for 2 days. Samples were taken for analysis, and the
remaining algae and Daphnia were placed in separate solutions not containing
cacodylic acid. Two fish were added to the untreated solutions containing
Daphnia, and 4 snails were added to the untreated solutions containing algae.
Two fish and 4 snails were also added to the treated solutions from which
algae and Daphnia had been removed. All fish were harvested after 2 days,
and 2 snails were harvested after 7 days.
Fish and snails accumulated 2 to 10 times more cacodylic acid from solu-
tion than they obtained by consuming cacodylic acid-treated Daphnia or algae.
Only a limited supply of treated Daphnia was available to the fish, and it
is not known whether or not a larger supply would have resulted in more
accumulation of cacodylic acid residues. By contrast, the snails had an ample
supply of algae, but after 7 days they also accumulated less cacodylic acid
from algae than from treated solution. The authors concluded that under the
conditions studied, uptake "prom solution was more important than consumption
of one food chain organism by another, especially for the algae-snail part of.
the food chain.
The authors commented that there was considerable variability between
replications, and that this seems to be an inherent problem in working with
complex, multiorganism systems. Nevertheless, they consider the ecosystem a
useful tool for indicating the likely behavior of compounds in the environ-
ment.
In response to the current concern over the distribution of pesticides.in
the environment, Schuth et al. (1974) reexamined the accumulation of cacodylic
acid in an experimental aquatic ecosystem using different aquatic organisms.
The model ecosystem used by Isensee et al. (1973) was considerably reorganized
to include bottom feeding organisms (catfish, Ictalurus punctatus; and cray-
fish, Procambarus clarki) indigenous to cotton-producing areas, and duckweed,
Lemna minor L. Three soils from a cotton-producing region in Texas, namely. .
Hidalgo clay loam, Laredo silt loam, and Willacy sandy loam, were treated
with a mixture of -^C-labeled and unlabeled cacodylic acid so as to contain
21.4 ppm of cacodylic acid, a rate which approximately equals the concentration
in the upper 3.8-cm layer of soil after application of the highest rate used in
the field. After mixing, the soils were layered on the bottom of separate
110-liter glass tanks; covered with pea-gravel and aluminum window screen;
flooded with 80 liter of distilled water; and allowed to equilibrate for 1 week
without aeration. One control tank each of the Hidalgo and Laredo soils were
also prepared, containing all components except the cacodylic acid. After 1.
week, aeration was started and 7 catfish, 3 crayfish, several hundred daphnids,
10 snails, several hundred mg of filamentous algae, and 10 to 20 duckweed
plants were added to each tank. Catfish and crayfish were fed brine shrimp and
chopped perch, respectively, every 3 to 4 days. A screen was used to vertically
bisect the tanks to protect the catfish from the predacious crayfish.
Twenty-three days after the organisms were added, an infestation of cray-
fish by parasitic Lerneus species made it necessary to harvest all organisms.
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About 12.5 ppm of KMh04 was added to each tank 1 and 5 days later to kill the
parasites. A second group of organisms was added 9 days later and harvested
aftei 20-day exposure; no parasites were observed in this compliment. The
and arsenic contents were determined intermittently in each component of the
ecosystem over the 60-day experimental period.
After 59 days, 13.5% of the l^c radioactivity and 40.0% of the arsenic
from the cacodylic acid originally supplied remained in the soil- (average of
the 3 soils). The differential losses of -^C and arsenic indicate that the
carbon- arsenic bond of cacodylic acid is split in soil (Woolson and Kearney
1973). The cacodylic acid concentration in water, based on total radioacti-
vity, increased almost linearly throughout the first 30 days, then leveled
off, and finally decreased.
In another experiment, it was determined that KMnO^ did not destroy
cacodylic acid, even when being heated during distillation of arsine. Compari-
sons between the l^C activity and the distribution of arsenite, arsenate, and
total arsenic in the water at 5 different points in time during the experiment
led to the conclusion that the cacodylic acid wad degraded in at least 2 or
3 of the soils studied. The aquatic organisms accumulated considerably more
C than arsenic, indicating that the cacodylic acid was degraded, with subse-
quent uptake of ^C by the plant life. Autoradiographs of thin layer chroma-
tograms of snail and algae extracts failed to show any parent cacodylic acid
storage in these organisms. However, in- the first harvest of organisms,
crayfish did accumulate detectable amounts of arsenic. The arsenic was measured
in terms of Bioaccumulation Ratio (calculated as the concentration of arsenic
in tissue divided by the concentration of arsenic in water ) . Ratios for the
first harvest of crayfish ranged from 4.2 to 5.2 (Isensee et al. 1973).
A material balance for the arsenic in the model ecosystem shows that 5,
31, and 48% of the arsenic initially added to the 3 soils was lost during the
experiment. A garlic-like odor was observed above the tanks on day 25 of the
experiment. The authors suggested that it may have been dimethylarsine which
is known to have such an odor. Quantitative differences in arsenic lost from
the different soils may reflect differences in the populations of microorganisms
capable of reducing cacodylic acid to volatile derivatives, and/or differences
in the ability of the soils to retain arsenical compounds. In relation to the
total arsenic in the system, the biomass was an insignificant sink for arsenic.
The authors concluded that cacodylic acid does not bioaccumulate in the
aquatic organisms studied. Cacodylic acid was degraded to ^C-containing
products and inorganic arsenate, and reduction to volatile organoarsenical
compounds may account for the observed loss of arsenic from the system.
Environmental Transport Mechanisms
In a proposed environmental cycle for arsenic, Woolson (1974) stated that
the major inputs into the system come from air and water pollution arid from the
use of pesticides. . Soil is the sink to which arsenic ultimately returns.
87
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Arsenic reaches man through air, water, and food. Ar senate which is ingested
is eliminated and returns to the water or soil phases of the environment.
Plants and animals receive arsenic from air or water pollution, from the soil,
or from pesticide use. Arsenicals reaching the soil may begin the cycle of
chemical transformation, precipitation and/or uptake once again.
According to McBride and Wolfe (1971) , arsenate may be converted to
dimethylarsine by a number of reduction and methylation steps in which, MAA and
cacodylic acid are intermediates. Cacodylic acid and , MAA can also yield di-
methylarsine when subject to the same conditions as arsenate. Woolson (1974)
suggests that the arsines produced are probably oxidize^ back to MAA or caco-
dylic acid, or demethylated and returned to the arsenate form in the soil.
Methylation as Well as demethylation can occur in the soil medium.
Bfamah arid Foreback (1973) recently reviewed the available information
conceftiiiig methylated forms of arsenic in the environment, and analyzed
nanogifam amounts. They detected trivalent arsenic, pentavalent arsenic, MAA
and dimethylarsinic acid .in samples of freshwater, saline water, bird eggshells,
seaghe3!i?§, and "hinfian urine. Since they are identical. with the biologically
produced 'me thy larsenic acids, the detection of the effect of adde4 methylarsenic
pesticides "will Be difficult. The continued introduction of arsenic ; compounds
into the environment; via pesticides and other human activity may eventually
result 'in *a general i/ncrease in their concentrations -in water and air due. to
the fracterial" mobilization of all forms of arsenic. ught -in
Norwe|ia*fr-ocea!n-i^ate-r^: 5.2 to 21.6 ppm for herring (Clupses har.engus)-. 3.1
ppm fb'r ifiacket:el (Scomber se'dftiber) . and 7.9 ppm for capelin (Mallotus villosus)
The data regarding the behavior of cacodylic acid in soil and water,
although limited, indicates that movement of cacodylic acid from treated land
to water "by leaching or surface runoff appears to be minimal or nil. The
observations frbm the treatment of irrigation ditchbanks with cacodylic acid
support this conclusion. Cacodylic acid residues in the soil do not appear to
be persistent. Accumulation of phytotoxic residue levels qf the unchanged
parent compound in the soil therefore appears very unlikely.
In a study o'f 5 annual applications of cacodylic acid to a sandy clay
loam by the Ansul Company (1973) , no increase in the amount of arsenic in the
88
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plow layer was observed. Reduction of nrganoarsenicals to volatile methyl-
afsines and their subsequent environmental redistribution were given as a
possible explantion for lack of arsenic buildup in this study.
However, gradual accumulation of arsenic-containing degradation products
in soils appears to be possible, especially in areas of heavy use of organo-
arsenical pesticides. Cotton fields receiving multiple applications of
cacodylic acid and two other arsenicals used as defoliants would be an example.
Little information seems to be available on the possible magnitude and
significance of such arsenic buildup.
Furthermore, several studies reported above indicate that following
application of cacodylic acid (and other organoarsenical pesticides),
substantial quantities of arsenic escape to the air in the form of volatile,
biologically active degradation products.
89
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Ehman, P. J., "Residual Effects of Cacodylic Acid on Seven Crops," Fate of
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j
Ehman, P. J., "Movement of Cacodylic Acid in Treated Soils," Fate of
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Wisconsin (1963c).
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Ehman, P. J., "Report on Phytotoxicity of Smoke from Burning Grass Previously
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Ehman, P. J., "Report on the Residual Effects of Cacodylic Acid ('Ansar1 138)
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Hughes, J. S. (Louisiana Wildlife and Fisheries Commission), Letter to The
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Industrial Bio-Test Laboratories, "Sodium Cacodylate, 8-Day Dietary LC5Q Study
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in Mallard Ducklings," submitted to The Ansul Company, Marinette, Wisconsin
(1973b).
Isensee, A. R., P. C. Kearney, E. A. Woolson, G. E. Jones, and V. P. Williams,
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Lehn, P. J., A. L. Young, N. A. Hamme, and B. C. Wolverton, Studies to Determine
the Presence of Artificially Induced Arsenic Levels in Three Freshwater Streams
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Macklin, C. E., and M. Witkamp, "Decomposition of Leaf Litter From Tulip Poplar
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Malone, C. R., "Responses of Soil Microorganisms to Nonselective Vegetation
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507-512 (1972).
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32531-71208, The Ansul Company, Agrichemical Development Center, Weslaco,
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in: L. A. Norris (ed.), The Behavior and Impact of Organic Arsenical
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.1 " - ,
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PART II. INITIAL SCIENTIFIC REVIEW
SUBPART D. PRODUCTION AND USE
CONTENTS
Page
Registered Uses of Cacodylic Acid 98
Federally Registered Uses 98
State Regulations 101
Production and Domestic Supply Ill
Volume of Production Ill
Imports Ill
Exports Ill
Domestic Supply Ill
Formulations Ill
Use Patterns of Cacodylic Acid in the United States 112
General 112
Cacodylic Acid Uses by Functions and Areas 113
Cacodylic Acid Uses in California 115
References 122
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This section contains data on the registration, and on the production and
uses of cacodylic acid. The section summarizes rather than interprets data
reviewed.
Registered Uses of Cacodylic Acid
Federally Registered Uses - Cacodylic acid, also known as dimethylarsinic acid,
or hydroxydimethylarsine oxide, is a contact herbicide that will defoliate or
desiccate a wide variety of plants. It is nonselective in its action and is
useful for general postemergence weed control. It does not have any pre-
emergence herbicidal activity. Upon contact with green vegetation, cacodylic
acid is absorbed into plant cells, killing them. Cacodylic acid's only apparent
translocation is apoplastic. Appropriate surfactants are either
included in formulated products, or may be added to the spray tank if they are
not already contained in the formulation. Small quantities of cacodylic acid
are used for tree killing and bark beetle control purposes in forest management.
Two basic manufacturers produce cacodylic acid in the United States—The
Ansul Company, Marinette, Wisconsin, and Vineland Chemical Company, Inc., Vineland,
New Jersey. Each company markets several different herbicide formulations
containing cacodylic acid as sodium salt or acid by itself or in combination
with other herbicides. In addition, a specialty formulation of cacodylic acid
for tree killing purposes is available through the TSI Company, Flanders, New
Jersey. (See subsection on Formulations, p. 111.)
Registered cacodylic acid uses and application rates are listed as follows:
1. General weed control in noncrop areas such as drainage ditchbanks;
rights-of-way; along sidewalks, driveways and fences; along railways,
highways and other roads; around buildings, ornamentals, lumber yards,
grain elevators, parking lots, etc.
Rate: 2.5 to 5.0 Ib acid equivalent per 100 gal of water, applied
at a volume sufficient to cover the unwanted vegetation to just short
of run-off. Reapply as required (no limitations).
2. Weed control as a "directed application" in nonbearing citrus orchards
(orange, grapefruit, tangerine, lemon and lime orchards), to be
applied in interspaces between, and around the base of trees.
Rate: 3.75 to 5.0 Ib acid equivalent per acre, to be mixed with
water at the rate of 2.5 to 5.0 Ib acid equivalent in 50 to 100 gal,
and applied as a full-coverage spray to just short of run-off.
Application should be repeated as required if regrowth occurs, but
no more than 3 applications per year are permitted. This use is
not permitted in Florida.
3. Lawn renovation by application of cacodylic acid to lawn mowed to
about 1 in height, preferably on a warm, sunny day.
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Rate: About 8.5 Ib acid equivalent per acre, equal to 3 oz of acid
equivalent per 1,000 sq ft, in 4 gal of water. This rate corresponds
to 10 fluid ounces of a cacodylic acid formulation containing 2.5 Ib
acid equivalent per gallon in 4 gal of water per 1,000 sq ft.
If green areas remain, reapply after 5 days. When top growth is all
brown, dead vegetation should be removed, and the lawn may be
promptly re-established because the phytotoxic properties of cacodylic
acid are quickly inactivated on contact with soil.
4. Defoliation of irrigated and dryland cotton by aerial or ground
application, to be applied when 50% or more of the cotton bolls are
open, and 7 to 10 days prior to anticipated picking.
Rate: On dryland cotton, about 0.8 to 1.0 Ib acid equivalent per
acre. In airplane applications, 5 to 10 gal of water should be used,
and 15 to 25 gal of water per acre for ground applications.
5. For general postem^rgent weed control in noncrop areas, a combination
product is registered and recommended that contains MSMA and cacodylic
acid at the ratio of 2.4 parts MSMA and 1 part cacodylic acid. This
combination offers quick burn-down of vegetation in conjunction with
the systemic effect necessary to control certain deep-rooted
perennial grasses and weeds. Weeds against which this combination
product is registered and recommended include puncture vine, wild
mustard, wild oats, chickweed, sandburn, common ragweed, pigweed,
crabgrass, lambs-quarter, common plantain,'prostrate spurge, giant
foxtail and yellow foxtail. It provides top-kill of certain perennial
grasses such as Johnson grass, dallisgrass and nutsedge.
Rate: 4.25 to 8.5 Ib of combined active ingredients in 40 to 100
gal of water per acre. Reapply as required.
6. Crown kill of undesirable trees, including both conifers and hardwoods,
through spaced-cut injection methods.
Rate: About 1 ml of a formulation containing 50% cacodylic acid
per cut per 2 in of tree diameter at breast height (DBH) for trees
below 8 in DBH; 1 iol of 50% formulation per cut per 1 in DBH for
trees 8 in DBH and larger.
Rate: Recommended rates vary somewhat depending upon whether conifers
or hardwoods are to be killed, and whether the treatment is made
during the growing or the dormant season. (See Table 12, p. 105.)
7. Park, beetle, control is used by nrofessional foresters and ento-
mologists only: cacodylic acid can also be employed to control
Southern pine beetle (Dendroctonus frontalis), spruce beetle
(Dendrectonus rufipennis), Engelmann spruce beetle (Pendroctonus
obesus), mountain pine beetle (Dendroctonus ponderosae), Douglas-
fir beetle (Dendroctonus pseudotsugae), round-headed pine beetle
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(Dendroctonus adjunctus), Arizona 5-spined beetle (Ips lecontei),
pine engraver beetle (Ips pini), and the California 5Hspined beetle
(Ips confusus). Suggested uses include: pre-flight treatment (trap
tree technique), pre-harvest treatment (elimination of logging debris
as brood material), pre-cutting treatment (in areas to be disturbed
as, for instance, in trail building), and post-flight treatment
(lethal trap technique).
Rate: For best results, a complete, trough-like frill has to be
made around the entire tree within 18 in of the ground. One milli-
liter of a 50% cacodylic acid formulation per inch of tree cir-
cumference is to be applied evenly in the frill. Pre-flight treat-
ment (for spruce beetle only) may be made in October, with treated
trees to be felled 4 weeks after treatment, or in the spring, 4 to
8 weeks before peak bark beetle emergence, with treated trees to be
felled 2 to 4 weeks after treatment. Pre-harvest and pre-cutting
treatments involve treating 4 weeks prior to cutting the tree. Post-
flight treatments should be made within 2 to 3 weeks after the tree
is attacked. (For further details, refer to table 13, page 105.)'
Specimen labels for 2 widely used weed control formulations of cacodylic
acid, a cotton defoliant formulation and a forestry use formulation, are
included in this report. The labels give a complete overview of these regis-
trations, including the range of dosage rates, general and specific directions
for use, use limitations, caution statements and other fetails relevant to
commercial use.
1. Table 10: Cacodylic acid formulation containing: 22.73% sodium
cacodylate; 3.88% cacodylic acid; 12.75% total elemental arsenic,
all in water soluble form; 2.48 Ib cacodylic acid equivalent per
gallon. This product also contains a surfactant.
Product name: Phytar 560 Herbicide
Manufacturer: The Ansul Company, Marinette, Wisconsin
EPA Registration No.: 6308-20
2. Table 11: Cacodylic acid formulation containing: 27.38% sodium
cacodylate; 4.67% cacodylic acid; 15.41% total elemental arsenic,
all in water soluble form; 3.1 Ib cacodylic acid equivalent per
gallon. This product also contains a surfactant.
Product name: Bolls-eye Cotton Defoliant
Manufacturer: The Ansul Company, Marinette, Wisconsin
EPA Registration No.: 6308-91-AA
3. Table 12: Cacodylic acid formulation containing: 50.0% cacodylic
acid; 27.1% total elemental arsenic, all in water soluble form;
6.0 Ib cacodylic acid equivalent per gallon. This product also
contains a surfactant.
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Product name: Silvisar 510 Tree Killer
Manufacturer: TSI Company, Flanders, New Jersey
EPA Registration No.: 28301-2
4. Table 13; Directions for the use of cacodylic acid for bark beetle
control (by professional foresters and entomologists only).
5. Table 14; Cacodylic acid and MSMA formulation containing: 26.02%
MSMA; 10.47% sodium cacodylate; 1.80% cacodylic acid; 17.92% total
elemental arsenic, all in water soluble form; 3.0 Ib MSMA and 1.25
Ib cacodylic acid equivalent per gallon. This product also contains
a surfactant.
Product name: Broadside Herbicide
Manufacturer: The Ansul Company, Marinette, Wisconsin
fitate Regulations - Toxicity studies indicate that cacodylic acid is not
highly toxic to mammals, ^ome states that regulate the use of pesticides have
placed special restrictions on pesticides which are highly toxic or otherwise
hazardous to human and/or environmental health. For instance, in California,
42 specific pesticides have been designated as "injurious or restricted mate-
rials." The use of pesticides in this category is subject to special restric-
tions under regulations administered by the California State Department of
Agriculture.
The California list of "injurious materials" includes "certain arsenic
compounds,'1 which include inorganic trivalent arsenicals and inorganic
pentavalent aresnates, but not organic pentavalent arsenates, such as cacody-
lic acid. Therefore, cacodylic acid is not subject to special restrictions
in California or, as far as is known, in any other state.
101
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Table 10. CACODYLIC ACID (2.48 LB ACID EQUIVALENT PER GALLON)
HERBICIDE SPECIMEN LABEL
Herbicide
Sodium Cacodylate
and Cacodylic Acid >
Liquid Plus Surfactant ««r ._
For General
Post-Emergent
Weed Control
ACTIVE INGREDIENTS:
Sodium Cacodylate ... 22.73%
DimethylariNiic Acid
(Cacodylic Acid) .... 3.88%
INERT INGREDIENTS: 73.39%
Total Arsenic (as elemental)
all in water soluble
form ...... 12.75%
Product contai':.- 2.48 Ibs.
cacodylic acid equivalent
per gallon.
CAUTION:
Keep out of the
reach of children
Read entire label
before using
this product /
/ SPECIMEN LABEL
nrtHj *.«.•-• -tf
102
-------
Table 10. (Continued)
CAUTION: Keep Out of the Reach of Children
CAUTION: H.irmfiil if swallowed Avon! con:.irt with >km. Avoid hreathmg spicty misl. Wash hands after
using. Avoul sloiane near feed 01 food products. Keep chiUlu-n and domestic animals off treated areas until
this material has been washed into the soil.
Do not contaminate waters used for domestic consumption, or by animals, wildlife and aquatic life, or for
irrigation purposes. Do not graze treated areas to livestock.
ANTIDOTE: II taken internally, induce vomiting and Cdll physician at once.
READ ENTIRE LABEL BEFORE USING THIS PRODUCT.
WARRANTY - CONDITION OF SALE: DIRECTIONS FOR USE of this product are based on field use
and tests believed reliable and should be followed caiefuMy. It is however impossible to eliminate all risks
associated with use ol this product. Because such factois as weather conditions, foreign material and manner
of use for application are all beyond the control of The Ansul Company or the Seller of this product, such
things as crop injury, ineffectiveness or other unintended consequences may result. ALL SUCH RISKS ARE
ASSUMED BY THE BUYER.
Ansul warrants that this pioduct confonns to the chemical description on the label and is reasonably fit for
the purposes referred to in the directions for use as modified by the above. Ansul makes no other warranties,
express or implied, including FITNESS or MERCHANTABILITY. In no case shall Ansul or the Seller be
liable for consequential, special or indirect damages resulting from the use or handling of this product. The
foregoing is a condition of sale by The Ansul Company and is accepted as such by the Buyer.
GENERAL INFORMATION: PHYTAR 560 Herbicide is useful for geneial post-emergent weed control. It
is non-selective in its action.. Its phytotoxic properties are quickly inactivated on contact with soil. It
contains a surfactant. It is unnecessary to add any other surfactant to the spray solution. Best results are
obtained on young actively growing weeds. It produces top-kill only, so repeat applications are required for
season long weed contiol of perennials.
MIXING INSTRUCTIONS: PHYTAR 560 Herbicide is completely water soluble. Any spray equipment
that gives good coverage may he used. Fill the spray tank about hall full with water and add the required
amount of herbicide with agitation. Finish filling the tank with water and apply. After use, clean equipment
thoroughly by flushing with water. Do not stoie spray solution in tank for a prolonged period. Although
PHYTAR 560 Herbicide is only moderately corrosive, do not use in galvanized or aluminum equipment.
CONTAINER DISPOSAL: Do not reuse empty container. Wash thoroughly with water and detergent.
crush if possible, and discaid in a sale place.
DIRECTIONS FOR USE:
NON-CROP: PHYTAR 560 Herbicide is useful for general weed control on drainage ditchbanks and rights-
of-way, along sidewalks, driveways and fences, around buildinqs and ornamentals, and on similar non-crop
areas. Mix 1 to 2 gallons of PHYTAR 560 Herbicide in 100 gallons of water. Spray unwanted vegetation to
just short of run-off. If regrowth occurs reapply as required.
Do not allow spray to come in contact with foliage, green bark, grafted unions, or scuffed, damaged or
broken bark when spraying around trees and ornamentals.
AGRICULTURAL-PLANTINGS - CITRUS (Except Florida): PHYTAR 560 Herbicide is useful as a directed
application in non-bearing citrus orchards such as orange, grapefruit, tangerine, lemon and lime orchards. It
should be applied at the rate of 1VS to 2 gallons per acre.
Mix 1 to 2 gallons of PHYTAR 560 Herbicide in 50 to 100 gallons of water. Apply as a directed spray
in interspaces and around base of trees. Spray unwanted vegetation to just short of run-off. If regrowth
occurs, reapply as requited, however, do not exceed 3 applications per year.
Do not allow spray solution to contact leaves, stems or bark. Use a shield, if necessary, for nursery plantings
or young trees. Do not apply around trees from which fruit will be harvested within one year of treatment.
LAWN RENOVATION: Mow lawn to about 1 inch high before treatment. Mix 10 fluid ounces of PHYTAR
560 Herbicide in 4 gallons of water and apply to 1,000 sq. ft. Spray foliage thoroughly, preferably on a
warm sunny day, foliage will usually turn brown in about five days. Bermudagrass and other deep-rooted
perennials, or partially sprayed foliage, may require a second treatment. Reapply five days later if qreen
areas remain.
When foliage is all brown, matted areas should be raked to remove dead vegetation. The lawn may then be
re-established according to local practice.
Keep children and pets off treated areas until after first rain 6r sprinkling following treatment. Do not
track from treated to untreated areas.
PHYTAR 560 Herbicide is manufactured by The Ansul Company, Marinette, Wisconsin 54143.
U.S. Patents 3.173,937 and 3,056.668 and others pending.
/.SI. PHYTAR and ANSUL are registered trademarks of The Ansul Company.
Net Contents 5 Gallons EPA Reg. No. 6308-20
Form No. C-7384
THE ANSUL COMPANY,
MARINETTE, WISCONSIN
103
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Table 11. CACODYHC ACID (3.1 LB ACID EQUIVALENT PER GALLON)
COTTON DEFOLIANT SPECIMEN LABEL
Bolls-eye
O«**ftn riafnlian* • ^^^
Cotton Defoliant
Sodium Cacodylate
and Cacodylic Acid
Liquid Pius
Surfactant
For Use As A
Defoliant For
Irrigated and
Dryland Cotton
TM
ACTIVE INGREDIENTS:
Sodium Cacodylate .
Dimethylarsinic Acid
(Cacodylic Acid)
INERT INGREDIENTS.
Total Arsenic (as elemental)
all in water soluble
form ... ... 15.41%
Product Contains 3.10 tbs.
Cacodylic Acid Equivalent
Per Gallon.
CAUTION:
Keep out of the
reach of children
Read entire label
before using
this product
SPECIMEN LABEL
104
-------
Table 11. (Continued)
CAUTION: Keep Out of the Reach of Children
CAUTION: Harmful if swallowed. Avoid contact with skin. Avoid breathing spray mist. Wash hands
after using. Avoid storage near feed or food products. Keep children and domestic animals off treated
areas until this material has been washed into the soil.
ANTIDOTE: If taken internally, induce vomiting and call physician at once.
READ ENTIRE LABEL BEFORE USING THIS PRODUCT.
PATENT NOTICE: The price of this product includes the royalty of 10 cents per pound (for a
license to use the contents hereof under the claims of U.S. Patent No. 3,378,364). A license under
the said patent is available to anyone who wishes to practice the patented method with materials
obtained from other sources.
WARRANTY - CONDITION OF SALE: DIRECTIONS FOR USE of this product are based on
field use and tests believed reliable and should be followed carefully. It is however impossible to
eliminate all risks associated with use of this product. Because such factors as weather conditions,
foreign material and manner of use for application are all beyond the control of The Ansul Company
or the Seller of this product, such things as crop injury, ineffectiveness or other unintended con-
sequences may result. ALL SUCH RISKS ARE ASSUMED BY THE BUYER.
Ansul warrants that this product conforms to the chemical description on the label and is reasonably
fit for the purposes referred to in the directions for use as modified by the above. Ansul makes no
other warranties, express or implied, including FITNESS or MERCHANTABILITY. In no case shall
Ansul or the Seller be liable for consequential, special or indirect damages resulting from the use or
handling of this product. The foregoing is a condition of sale by The Ansul Company and is accepted
as such by the Buyer.
GENERAL INFORMATION: BOLLS-EYE Cotton Defoliant is used as a harvest aid for the
defoliation of cotton. Its phytotoxic properties are quickly inactivated on contact with the soil. It is a
combination of a defoliating agent and surfactant. It is desirable to add additional surfactant when
using ground application equipment (see use directions), none need be added for aerial application.
CARE OF EQUIPMENT: Although BOLLS-EYE Cotton Defoliant is only moderately corrosive,
do not apply with any applicator that is lined with zinc, tin, or aluminum.
MIXING INSTRUCTIONS: BOLLS-EYE Cotton Defoliant is completely water soluble. Fill the
spray equipment reservoir about half full with water and add the required amount of defoliant with
agitation. Finish filling the reservoir with water and apply. After use, clean equipment thoroughly by
flushing with water. Do not store spray solution in tank for a prolonged period.
CONTAINER DISPOSAL: Do not reuse empty container. Wash thoroughly with water and
detergent, crush if possible and discard in a safe place.
Do not contaminate waters used for domestic consumption, or by animals, wildlife and aquatic life,
or for irrigation purposes. Do not feed treated foliage to livestock or graze treated areas.
DIRECTIONS FOR USE: BOLLS-EYE Cotton Defoliant is useful as a harvest aid for the defoliation
of irrigated and dryland cotton with aerial or ground application equipment. For the most effective
defoliation, good coverage of all leaves is essential.
Nozzles must be arranged to provide thorough coverage of the foliage. If applied by airplane, use
5 to 10 gallons of water per acre. This range will generally provide adequate coverage. If applied by
ground equipment, a spray volume of 15 to 25 gallons of water per acre is preferred. With ground
application equipment and at spray volumes of 15 to 25 gallons per acre, add 1/3 to 2/3 pints of a
suitable surfactant.
DEFOLIATION OF DRYLAND COTTON: Apply 2 to 2.5 pints of BOLLS-EYE Cotton Defoliant
per acre when 50% or more of the bolls are open and 7 to 10 days prior to anticipated picking.
DEFOLIATION OF IRRIGATED COTTON: Apply 2.5 to 3 pints of BOLLS-EYE Cotton
Defoliant per acre when 50% or more of the bolls are open and 7 to 10 days prior to anticipated
picking.
BOLLS-EYE Cotton Defoliant is manufactured by The Ansul Company, Marinette, Wisconsin 54143.
/(,•!. ANSUL are registered trademarks of The Ansul Company.
Net Contents 5 Gallons EPA Reg. No. 6308-91-AA
Form No. C-7374
THE ANSUL COMPANY.
MARINETTE. WISCONSIN
105
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Table 12. CACODYLIC ACID (6.0 LB ACID EQUIVALENT PER GALLON)
TREE KILLER SPECIMEN LABEL
Tree Killer
For General Forestry Use
ACTIVE INGREDIENTS:
Dimethylarsinic Acid
(Cacodylic Acid) 50.0%
INERT INGREDIENTS:. . . 50.0%
Total Arsenic (as elemental)
all in water soluble
form 27.1%
Product contains 6.0 Ibs.
dimethylarsinic acid equivalent
per gallon.
CAUTION:
Keep out of the
reach of children
Read entjre label
before using
this product
SPECIMEN LABEL
106
-------
Table 12. (Continued)
CAUTION: Keep Out of the Reach of Children
CAUTION: Harmful if swallowed. Avoid contact with skin. Wash thoroughly after using. Store in a
safe place away from feed and food products.
ANTIDOTE: If taken internally, induce vomiting and call physician at once
READ ENTIRE LABEL BEFORE USING THIS PRODUCT.
WARRANTY - CONDITION OF SALE: DIRECTIONS FOR USE of this product are based on field
use and tests believed reliable and should be followed carefully. It is, however, impossible to eliminate
all risks associated with use of this product. Because such factors as weather conditions, foreign mater-
ial and manner of use for application are all beyond the control of TSI Company or the Seller of this
product, such things as crop injury, ineffectiveness or other unintended consequences may result ALL
SUCH RISKS ARE ASSUMED BY THE BUYER.
TSI Company warrants that this product conforms to the chemical description on the label and is rea-
sonably fit for the purposes referred to in the directions for use as modified by the above. TSI makes
no other warranties, express or implied, including FITNESS or MERCHANTABILITY. In no case shall
TSI or the Seller be liable for consequential, special or indirect damages resulting from the use or
handling of this product. The foregoing is a condition of sale by TSI Company and is accepted as such
by the Buyer.
GENERAL INFORMATION: SILVISAR 510 Tree Killer is designed for crown kill of undesirable
trees, including both conifers and hardwoods, through spaced-cut injection methods. It shows negligi-
ble translocation through root grafts and has no residual phytotoxic action in the soil.
CARE OF EQUIPMENT: SILVISAR 510 Tree Killer is entirely soluble in water. Although SILVISAR
510 Tree Killer is only moderately corrosive, do rot apply with any applicator that is lined with zinc,
tin, or aluminum. Rinse all injection equipment thoroughly after use, and dispose of liquid wastes in a
pit in non-crop lands located away from water supplies.
CONTAINER DISPOSAL: Do not reuse empty container. Wash thoroughly with water and detergent,
crush if possible, and discard in a safe place
DIRECTIONS FOR USE:
SPACED-CUT INJECTION WITH TSI "HYPO-HATCHET" INJECTOR: The TSI HYPO-HATCHET
Injector cuts and injects in one operation. When a tree is struck with the injector, a pre-set amount of
SILVISAR 510 Tree Killer is injected automatically into the sap stream of the tree immediately after
impact. The injector works by inertia and is calibrated to inject at least one milliliter of chemical per
stroke. The cuts should be evenly spaced around the trunk to give proper distribution into the sap-
wood. For detailed instructions on how to use the TSI HYPO-HATCHET Injector, refer to the
Operation Manual.
CONIFERS AND HARDWOODS (Growing Season) - For trees below 8 inches diameter at breast
height (DBH), make one cut per 2 inches of DBH (454" spacing between cut edges) at waist height or
below. For trees 8 inches DBH and larger, make one cut per 1 inch DBH (154" spacinq between cut
edges).
CONIFERS (Dormant season) - Make one cut per 1 inch of DBH (154" spacing between cut edges)
at waist height or below.
HARDWOODS (Dormant season) - Make a complete frill at waist height or below.
SPACED-CUT APPLICATION: Although spaced-cut application is facilitated by use of the TSI
HYPO-HATCHET Injector, a hatchet or similar cutting tool can be used. The number of cuts per tree
depends upon the size of the cuts and the volume to be injected, but in any case, should be sufficient
to Hold the silvicide without running down the trunk. The cuts should be evenly spaced around the
trunk to give proper distribution into the sapwood. Apply SILVISAR 510 Tree Killer with a pump-
type oil can, plastic squeeze bottle, or other suitable dispenser; however, do not apply with any ap-
plicator that is lined with zinc, tin, or aluminum.
CONIFERS AND HARDWOODS (Growing season) - For trees below 8 inches diameter breast height
(DBH), apply 1 milliliter of SILVISAR 510 Tree Killer per cut per 2 inches of DBH (6" spacing be-
tween cut centerlines) at waist height or below. For trees 8 inches DBH and larger, use 1 to 2 milliliters
per cut per 1 inch DBH (3'* spacing between cut centerlines).
CONIFERS (Dormant season) - Apply 1 milliliter of SILVISAR 510 Tree Killer per cut per 1 inch
of DBH (3" spacing between cut centerlines).
HARDWOODS (Dormant season) - Apply 1 milliliter of SILVISAR 510 Tree Killer per cut in a com-
plete frill at waist height or below.
SILVISAR 510 Tree Killer is manufactured by TSI Company, Flanders, New Jersey 07836.
SILVISAR, HYPO-HATCHET are registered trademarks U.S. Patent 3,173,937 and others pending.
NetContents Gallons EPA Reg. No. 28301-2
TSI COMPANY
FLANDERS, NEW JERSEY, U.S.A.
107
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Table 13. CACODYLIC ACID - DIRECTIONS FOR BARK BEETLE CONTROL
SILVISAR 510 TREE KILLER FOR USE IN BARK BEETLE CON-
TROL FOR USE BY PROFESSIONAL FORESTERS AND ENTO-
MOLOGISTS ONLY
SILVISAR 510 Tree Killer can be used to control Southern pine beetle (Dendroctonus
frontal is), Spruce beetle (D. rufipennis), Englemann spruce beetle (D. obesus), Mountain pine
beetle (D. ponderosae). Douglas-fir beetle (D. pseudtsugae), round headed pine beetle (D. ad-
junctus), Arizona five-spined beetle (Ips. lecontei), pine engraver beetle dps. pini). and the
California five-spined beetle (Ips. confusus) in treated trees. The treatment of trap trees in-
tended for harvest or cutting can serve as an aid in the control of these pests in a forestry man-
agement program in the states of Virginia, Georgia, Louisiana, Texas, Oregon, Utah, Idaho,
Wyoming and in the Rocky Mountains of South Dakota, Colorado, Arizona and New Mexico.
SUGGESTED USES
1) Pre-flight treatment (trap tree technique).
2) Pre-harvest treatment (elimination of logging debris as brood material).
3) Pre-cutting treatment (in areas to be disturbed, e.g., trail building).
4) Post-flight treatment (lethal trap technique).-
DIRECTIONS FOR USE IN CONIFERS:
Make a complete, trough-like frill around the entire tree within 18 inches of the ground. Apply
1 milliliter (approximately 1/30 of an ounce) evenly in the frill for each inch of tree circum-
ference.
1) Pro-Flight Treatment (for spruce beetle only)—
Fall Treatment — Treat in Octobet and fell 4 weeks after treating. Use half strength (diluted
with equal amount of water) or full strength SILVISAR 510 Tree Killer.
Spring Treatment — Treat 4-8 weeks before peak beetle emergence and fell 2-4 weeks after
treating. Use half strength (diluted with equal amount of water) of SILVISAR 510 Tree
Killer.
2) Pro-Harvest and Pre-Cutting Treatments (for all beetle species mentioned above)—Treat with
full strength SI-LVISAR 510 Tree Killer at least 4 weeks before cutting the tree. Allow a
minimum of 4 weeks between treating and felling.
3) Post-Flight Treatment (for all beetle species mentioned above)—Treat with full strength
SILVISAR 510 within 2-3 weeks after the tree is attacked.
Form No. 73173 Litho in U.S.A.
Source: TSI Company, Flanders, New Jersey
108
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Table 14. CACODYLIC ACID (1.25 LB ACID EQUIVALENT PLUS
MSMA 3.0 LB PER GALLON)
HERBICIDE SPECIMEN LABEL
Herbicide
MSMA Sodium Cacodylate
Liquid Plus Surfactant
For General
Post-Emergent
Weed Control
ACTIVE INGREDIENTS:
Monosodium Acid
Methanearsonate . . .
Sodium Cacodylate .
Dimethylarsinic Acid
(Cacodylic Acid) ....
INERT INGREDIENTS: 61.71%
Total Arsenic (as elemental)
all in water soluble
form 17.92%
Product contains 3.00 Ibs.
MSMA and 1.25 Ibs.
cacodylic acid equivalent.
per gallon.
CAUTION:
Keep out of the
reach of children
Read entire label
before using
this product
SPECIMEN LABEL
109
-------
Table 14.- (Continued)
CAUTION: Keep Out of the Reach of Children
CAUTION: Harmful if swallowed. Avoid contact with skin. Avoid breathing spray mist. Wash hands
after using. Avoid storage near feed or food products. Keep children and domestic animals off treated
areas until this material has been washed into the soil.
ANTIDOTE: If taken internally, induce vomiting and call physician at once.
READ ENTIRE LABEL BEFORE USING THIS PRODUCT.
WARRANTY - CONDITION OF SALE: DIRECTIONS FOR USE of this product are based on
field use and tests believed reliable and should be followed carefully. It is however impossible to
eliminate all risks associated with use of this product. Because such factors as weather conditions,
foreign material and manner of use for application are all beyond the control of The Ansul Company
or the Seller of this product, such things as crop injury, ineffectiveness or other unintended con-
sequences may result. ALL SUCH RISKS ARE ASSUMED BY THE BUYER.
Ansul warrants that this product conforms to the chemical description on the label and is reasonably
fit for the purposes referred to in the directions for use as modified by the above. Ansul makes no
other warranties, express or implied, including FITNESS or MERCHANTABILITY. In no case shall
Ansul or the Seller be liable for consequential, special or indirect damages resulting from the use or
handling of this product. The foregoing is a condition of sale by The .Ansul Company and is accepted
as such by the Buyer.
GENERAL INFORMATION: BROADSIDE Herbicide is a special formulation of herbicides in com-
bination with a surface-active (wetting) agent, for general post-emergent weed control. It is unnecess-
ary to add any other surfactant to the spray solution. This product is effective on both broadleaf
weeds and grasses. The phytotoxic properties of these materials are quickly inactivated on contact
with the soil. Best results are obtained on young actively growing weeds at air temperatures above
70« F.
MIXING INSTRUCTIONS: BROADSIDE Herbicide is completely water soluble. Fill the spray
equipment reservoir about half full with water and add the required amount of herbicide with agita-
tion. Finish filling the reservoir with water and apply. After use, clean equipment thoroughly by
flushing with water. Do not store spray solution in tank for a prolonged period.
CONTAINER DISPOSAL: Do not reuse empty container. Perforate, crush and bury in a safe place.
Drums may be returned to a drum reconditioner.
DIRECTIONS FOR USE:
BROADSIDE Herbicide is a post-emergent herbicide useful for controlling broadleaf weeds and
grasses, such as puncture vine, wild mustard, wild oats, chickweed, sandbur, common ragweed, pig-
weed, crabgrass, lambsquarter, common plantain, prostrate spurge, giant foxtail and yellow foxtail;
and to top-kill certain perennials such as johnsongrass, dallisgrass and nutsedge.
BROADSIDE Herbicide is useful for general weed control on drainage ditchbanks, rights-of-way, fence
rows, and storage yards; along highways, utility lines and pipe lines; around power plants and build-
ings, and on similar non-crop areas.
Use BROADSIDE Herbicide at the rate of 1 to 2 gallons per acre in sufficient water to get full cover-
age. Ground application normally requires 40 to 100 gallons of spray solution per acre. Any spray
equipment that gives good coverage may be used. If regrowth occurs, reapply as required.
Bindweed (Morningglory) control: Use T/4 to 2 gallons BROADSIDE Herbicide in 50 to 100 gallons
of water per acre. Make first application at first bloom, wetting foliage just short of run-off. Repeat
application as needed for top-kill, but limit to three applications per year.
Do not contaminate waters used for domestic consumption, or by animals, wildlife and aquatic life,
or for irrigation purposes. Avoid spray contact with foliage on fruit or food crops and ornamentals.
Do not pasture livestock on treated areas.
BROADSIDE Herbicide is manufactured by The Ansul Company, Marinette, Wisconsin 54143.
X. SI , BROADSIDE, ANSUL are registered trademarks of The Ansul Company.
Net Contents 5 gallons •'went P*"*™* EPA Reg. No. 6308-65
Form No. C-72136
THE ANSUL COMPANY,
MARINETTE, WISCONSIN
110
-------
Production and Domestic Supply
Volume of Production - The Tariff Commission (TC) annual reports for the 1970
to 1973 period list only one basic producer of cacodylic acid in the United
States—The Ansul Company, Marinette, Wisconsin. However, cacodylic acid has
also been produced by Vineland Chemical Company, Vineland, New Jersey. The
TC reports do not carry the production and sales volumes of cacodylic acid
individually. Cacodylic acid is included in the category "Pesticides and Re-
lated Products, Acyclic." The reported production volume of total active
ingredient (AI) for this composite group was 43,004,000 Ib in 1970, 25,780,000
Ib in 1971, 48,883,000 Ib in 1972, and 68,841,000 Ib in 1973.
Compared to other pesticides in this category, the production and sales
volume of cacodylic acid is so small that TC data is not useful in estimating
volumes. However, based on an independent survey of pesticide and trade
sources, Midwest Research Institute (MRI) estimated the 1973/1974 domestic
production volume as between 1.4 and 1.8 million Ib acid equivalent per year.
Imports - Based on an absence of data in TC reports on benzenoid and non-
benzenoid chemicals (TC Publication 601) and Department of Agriculture reviews
on pesticides, it appears that cacodylic acid has not been imported into the
United States, at least in significant quantities, in recent years.
Exports - Cacodylic acid is not specifically listed in Bureau of Census com-
modity descriptions on pesticide exports. The 1972 report lists a composite
export total of formulated herbicides as 38,867,237 Ib. Based on other sources,
MRI estimated that the export volume of cacodylic acid in 1972 was small,
probably not amounting to more than 100,000 to 200,000 Ib of acid equivalent.
Domestic Supply - Based on information presented in preceding subsections, MRI
estimated that domestic consumption of cacodylic acid in 1973 was 1.3 to 1.7
million Ib acid equivalent.
Formulations - Cacodylic acid is available to users in the United States in
several different concentrations and formulations. All of these are liquid
concentrates containing the active ingredient in water-soluble form, water as
the principal solvent, and varying amounts of surfactant(s). The most widely
used cacodylic acid formulations intended for foliar application (for weed"
control or for defoliation) all contain at least some surfactant. One formu-
lation (Table 11) recommends adding additional surfactant to the spray tank
for use with higher volumes of dilute spray.
Cadodylic acid formulations are offered by several suppliers under dif-
ferent tradenames or lines of tradenames, including Phytar ®£ Bolls-eye (S>*
and Broadside ® (Ansul); Rad-E-Cate ® and Chex-Mate ® (Vineland); and Silvi-
sar ©(TSI Company, previously Ansul).
Ill
-------
In the past, Ansul marketed cacodylic acid-containing herbicides under
the names, Ansar@138 or Phytar®138. These products are no longer mar-
keted, and the names ate obsolete. One leading cacodylic acid formulation,
Ansul's Phytar®560, containing 2.48 Ib of cacodylic acid equivalent per
gallon is characterized in Table 10.
A very similar product, also containing about 2.5 Ib^acid equivalent per
gallon, is offered by Vineland under the name Rad-E-Cate ^. Another Vineland
cacodylic acid formulation cpntains 3.1 Ib of acid equivalent per gallon; it
is identified as Rad-E-Cate^BS.
Ansul *s cacodylic acid cotton defoliant contains 3.1 Ib of acid equivalent
per gallon. (See Table 11.)
TSI's cacodylic acid tree killer formulation contains 50% of cacodylic
acid, equivalent to 6.0 Ib of acid equivalent per gallon. (See Table 12.)
At least two cacodylic acid-MSMA combination formulations are currently
marketed. One of these, Ansul's Broadside®, contains 3.00 Ib MSMA and 1.25
Ib cacodylic acid equivalent per gallon. (See Table 14.) A very similar for-
mulation, containing 26% MSMA, 10.5% sodium cacodylate and 1.8% cacodylic acid,
is offered by Vineland under the name Chex-Mate®.
All currently available cacodylic acid formulations are corrosive, the
degree of corrosiveness depending largely upon the concentration of cacodylic
acid in the formulation. Most labels recommend against using these products
in application equipment lined with zinc, tin or aluminum. All equipment
should be thoroughly rinsed after use, and spray solutions should not be stored
in spray tanks for prolonged periods.
There are no dry powder or granular formulations of cacodylic acid com-
mercially available.
Use Patterns of Cacodylic Acid in the United States
General - Cacodylic acid is an organic arsenical herbicide deriving from penta-
valent arsenic. Cacodylic acid is used for general, postemergent weed control
in noncrop areas and in nonbearing citrus orchards (this use not permitted in
Florida), as a cotton defoliant, and as a tree killing agent in forest manage-
ment practices. The registration of cacodylic acid as a cotton defoliant was
obtained only recently and it is believed to be the fastest growing use of
cacodylic acid at the present time.
For general weed control and for cotton defoliation, cacodylic acid
formulations are used as foliar sprays, diluted in water. Application is
generally made by ground equipment, except in cotton defoliation where appli-
cation by air is the preferred method of treatment.
112
-------
When used as a tree killer, the product is to be applied through spaced-
cut injections, at the rate of about 0.7 g Al/cut. This rate is obtained by
using about 1 ml of a formulation containing 5 Ib of cacodylic acid per gal-
lon per cut. Trees below 8 in diameter at breast height (DBH) require one cut
per 2 in of DBH, trees 8 in DBH and larger require one cut per 1 in DBH.
These rates are applicable to conifers and hardwoods during the growing season.
Treatment of smaller conifers (up to 8 in DBH) during the dormant season re-
quires twice that rate, for example, about 0.7 g of cacodylic acid active in-
gredient per cut per in DBH.
Applying these rates, 1 gal of cacodylic acid formulation containing 50%
AI will kill approximately 2,000 trees 4 in DBH in size during the growing
season or 1,000 such trees during the dormant season or 500 trees 8 in DBH in
size in either season.
In this use, the cacodylic acid formulation can be applied with pump-
type oil cans, plastic squeeze bottles or other suitable dispensers to cuts
made by hatchets or similar cutting tools. A tool combining both functions,
i.e., cutting and injecting the herbicide, is the Hypo-Hatchet® injector that
cuts and injects in one operation. When a tree is struck with the injector, a
preset amount of the cacodylic acid tree killer formulation is automatically
injected into the sap stream of the tree immediately after impact. The injec-
tor is connected by tube to a herbicide dispensing bottle attached to the
operator's belt. The herbicide is fed to the injector automatically (inertia
principle). The usefulness of this tool is not limited to cacodylic acid; it
works with any water-soluble herbicide suitable for the killing of trees.
Cacodylic acid for tree killing purposes.is used primarily on northern
hardwood species in the Pacific Northwest. It is not as effective on southern
hardwoods which prevail in other parts of the United States and represent the
largest part of the silvicide market.
Cacodylic Acid Uses by Functions and Areas - Table 15 presents an estimate of
the quantities of cacodylic acid used in the United States in 1973 by functions,
in terms of percentage of total U.S. use, and in terms of quantities of active
ingredient (as acid equivalent), assuming two different levels of use, i.e.,
1.4 million Ib (Case A), and 1.6 million Ib (Case B). RvR Consultants estimated
that the total U.S. use of cacodylic acid in 1973 ranged between 1.3 and 1.7
million Ib of acid equivalent. Based on the available information, the use
volumes assumed in Case A and Case B, respectively, appear to be plausible.
Time and resources available for this task did not permit further refinement
of these estimates, nor retrospective expansion.
According to Table 15, nonselective weed control and cotton defoliation
account for the primary domestic use of cacodylic acid in 1973. MRI estimated
that weed control makes up about 50%, and cotton defoliation about 40% of the
total. Forest management uses amount to about 20,000 Ib AI, about 1% of the
total consumption. All others combined, including lawn usage, make up the
balance, an estimated 5%, amounting to 70,000 to 80,000 Ib of acid equivalent.
113
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Table 15. ESTIMATED USES OF CACODYLIC ACID IN THE UNITED STATES
BY MAJOR FUNCTIONS AND AREAS OF USE, 1973
Function
Nonselective
weed control^./
Cotton defoliation
Forest management
All other uses.®/
Total United States use
Estimated
share of
total use
52%
42%
17.
5%
100%
Estimated use,
Ib of AEl/
Case A^
725,000
585,000
20,000
70,000
1,400,000
Case B£/
830,000
670,000
20,000
80,000
1,600,000
Primary area
of use
Western and
southern states
Cotton states
Northwest
All areas
a/ AE = acid equivalent.
b/ Case A: Assuming total U.S. use = 1,400,000 Ib AE.
£/ Case B: Assuming total U.S. use = 1,600,000 Ib AE.
d/ Including directed application in nonbearing citrus orchards.
e/ Including lawn renovation, and all. other (including nonregistered) uses.
Source: RvR Consultants, Shawnee Mission, Kansas.
-------
Information from the field indicates that the total volume of use of
cacodylic acid in the United States is on the increase, and that cotton
defoliation represents the most rapidly growing use.
Cacodylic Acid Uses in California - California keeps detailed records of
pesticide uses by crops and commodities which are published quarterly and
summarized annually. Table 16 presents the recorded uses of cacodylic acid
in California by crops and other use categories for the 1970 to 1973 period.
A total of 112,366 Ib of cacodylic acid were used in California in 1970; the
total dropped to 23,230 Ib in 1971, then increased again to 35,414 Ib in 1972
and to 153,335 Ib in 1973.
The California pesticide use report for 1970 lists cacodylic acid as
Ansar ** 138, while there are no entries under cacodylic acid or sodium cacodylate.
The 23,230 Ib reportedly used in 1971 are identified as cacodylic acid; there
are no entries under Ansar $•', or under sodium cacodylate. In the 1972 and
1973 reports, uses of cacodylic acid and sodium cacodylate in California are
reported separately; they have been totaled for each of these 2 years in
Table 16 and detailed individually in Tables 17 through 20.
Of the 112,366 Ib of cacodylic acid used in California in 1970 according
to the state report, 90,365 Ib, or about 80% of the reported total, were used
for nonagricultural purposes. The reports for 1972 and 1973 reflect the
increasing use of cacodylic acid as a cotton defoliant, small uses on a number
of other crops and substantially increasing uses along highways and other roads,
by governmental agencies and for nonagricultural purposes.
It appears, however, that the California statistics reflect only use
patterns, but not the total quantities of cacodylic acid actually used in the
state.
In California, cacodylic acid is not subject to the special restrictions
and reporting requirements imposed on the sale and use of pesticides designated
as "restricted or injurious materials." For this reason, the percentage of
all cacodylic acid uses reported to the California State Department of Agriculture
and included in its statistics is not as high as in the case of restricted
pesticides.
Tables 17 through 20 present the uses of Cacodylic acid and sodium cacodylate
in California in detail by crops and other uses, number of applications, pounds
of active ingredient and number of acres treated for 1972 and 1973, the 2 most
recent years for which such data is available. These tables expand and provide
further insight into the cacodylic acid uses in California in 1972 and 1973
presented in summary form in Table 16.
At the present time, no other state in the Union records or publishes
pesticide use data in comparable detail. Limitations of time and resources
available for this task did not permit development of estimates on the uses of
cacodylic acid by states or regions, crops, and other uses beyond the data
provided in Tables 15 through 20.
115
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Table 16. CACODYLIC ACID^/ USES IN CALIFORNIA BY MAJOR
CROPS AND OTHER USES, 1970 TO 1973
Year
Crop/use 1973 1972 1971 1970
(Pounds of active ingredient)
Cotton
Other crops^/
State highways and
county roads
Other uses£/ 43.098 17,976 17.621 90,365
Totals, all uses 153,335 35,414 23,230 ' 112,366
89,449
2,370
18,418
11,014
208
6,216
7
96
5,506
--
5,908
16,093
a/ Referred to as Ansar (D 138 in 1970 including sodium cacpdylate in
1972 and 1973.
b/ Including alfalfa, almonds, beans, citrus, grapes, lettuce, sugar-
beets, tomatoes and fallow (open ground). _;
£/ Including Federal, state county and city agencies; park departments;
school districts; reclamation, irrigation, flood control, water,
water resource and vector control districts; the University of
California; and uses on industrial, residential, turf and other.,
nonagricultural areas.
Source: California Department of Agriculture, Pesticide use reports for
1970, 1971, 1972 and 1973.
116
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Table 17. USE OF CACODYLIC ACID IN CALIFORNIA IN 1972 BY CROPS AND
OTHER USES, APPLICATIONS, QUANTITIES, AND ACRES TREATED
M
H
Commodity
Almond
City agency
Cotton
County agricultural commissioner
County or city parks
County road
Federal agency
Fallow (open ground)
Flood control
Industrial areas
Irrigation district
Nonagricultural areas
Orange
Other agencies
Recreational areas
Residential control
School district
State highway
Structural control
Sugarbeet
University of California
Vector control
Water areas
Water resources
Total
Applications
4
190
1
5
62
8
1
1
17
289
Pounds
108.09
563.63
2,558.16
4,060.15
150.24
234.09
331.13
16.48
2,306.02
2.46
1,035.89
484.94
18.42
1,029.52
0.49
674.39
825.15
4,455.91
10.41
8.24
180.18
17.04
65.78
1,738.19
20,875.00
Acres
435.00
26,107.00
70.00
3.25
1,719.24
140.00
1.00
35.00
155.25
28,665.74
Source: California Department of Agriculture, Pesticide Use Report 1972 (1972)
-------
H
00
Table 18. USE OF SODIUM CACODYIATE IN CALIFORNIA IN 1972 BY CROPS AND
OTHER USES, APPLICATIONS, QUANTITIES, AND ACRES TREATED
Commodity
City agency
Cotton
County agricultural commissioner
County or city parks
Fallow (open ground)
Industrial areas
Irrigation district
Nonagricultural areas
Other agencies
Residential control
School district
State highway
University of California
Vector control
Water areas
Water resources
Applications . Pounds
29.94
180 8,456.09
569.88
7.61
1 58.24
2 1-66
1,057.85
24 956.84
376.32
65.70
3.52
1,525.85
72.38
20.80
10 184.37
1,152.31
Acres
25,304.00
70.00
.75
958.58
121.00
Total 217 14,539.36 26,454.33
Source: California Department of Agriculture, Pesticide Use Report 1972 (1972).
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Table 19. USE OF CACODYLIC ACID IN CALIFORNIA IN 1973 BY CROPS AND
OTHER USES, APPLICATIONS, QUANTITIES, AND ACRES TREATED
VO
Commodity
Beans, dry edible
City agency
Conifer
Cotton
County agricultural commissioner
County or city parks
County road
Federal agency
Fallow (open ground)
Flood control
Industrial areas
Irrigation district
Lemon
Lettuce/head
Npnagricultural areas
Nonagricultural areas8.'
Orange
Other agencies
Pomegranate
Reclamation district
Residential control
School district
State highway
Turf
University of California
Vector control
Water areas
Water resources
Total
a/ Miscellaneous units
Source: California Department of
Applications
1
6
1,258
8
6
1
1
43
4
60
1
4
4
1,397'
Agriculture, Pesticide Use Report
Pounds
3.53
615.18
65.38
19,501.36
3,273.46
614.47
231.11
2,493.08
83.92
1,623.72
7.26
670.24
3.76
18.32
240.71
1.15
430.85
1,522.47
1.41
3.28
900.21
894.32
7,136.34
11.88
125.87
60.26
33.82
808.28
41,375.64
1973 (1973).
Acres
15.00
25.00
149,541.50
280.25
10.62
32.00
120.00
667.21
4
1,470.00
3.00
26.00
95.74
152,286.32
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Table 20. USE OF SODIUM CACODYLATE IN CALIFORNIA IN 1973 BY CROPS AND
OTHER USES, APPLICATIONS, QUANTITIES, AND ACRES TREATED
Commodity
Beans, dry edible
City agency
Cotton
County agricultural commissioner
County or city parks
County road
Federal agency
Fallow (open ground)
Flood control
Industrial areas
Irrigation district
Lemon
Lettuce/head
Nonagricultural areas
Nonagricultural areasS'
Orange
Other agencies
Pomegranate
Reclamation district
Residential control
School district
State highway - ^._ - -
Turf
University of California
V«cj:art control
Water. areas
Water resources
Applications
1
1,258
?
t
5
I
1
1
33
4
60
1
"4
4
Pounds
^•••••VBMHMMt
12.48
1,008.. 63
69,948.17
2,635.99
584.95
8.88
8,110.93
208.00
3,778*40
1.66
2,333.75
13.31
65.71
668.35
4.14
1,523.46
4,601.15
4.99
11.64
1,757.05
17175.77""
11*042.25
42.15
108.67
.,212.98
-' 119.57
1,975.71
Acres
15.00
149,541.50
250.00
2.00
32.00
120.00
645.57
4
1,470.00
3.00
26.00
95.74
Total
1,373
111,958.74
152,200.81
a/ Miscellaneous units.
Source: California Department of Agriculture, Pesfeicide Use Report 1973 (1973).
-------
References
State of California Department of Food and Agriculture, Pesticide Use Reports
for 1970, 1971, 1972 and 1973.
U.S. Department of Commerce, "U.S. Foreign Trade/Exports, Commodity by Country,"
FT 410 (1972).
U.S. Tariff Commission, Synthetic Organic Chemicals, U.S. Production and Sales,
TC Publication 681 (1970, 1971, 1972, 1973).
121
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PART III. EFFICACY AND PERFORMANCE REVIEW
CONTENTS
Page
Introduction 124
Efficacy of Pest Control 125
Weed Control 125
Hardwood Tree Control 125
Tree Insect Control 126
References 129
123
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This section contains a general assessment of the efficacy of cacodylic
acid. Studies on the production of cacodylic acid in the United States, as
well as an analysis of its use patterns at the regional level and by major
crop, were conducted as part of the Scientific Review (Part II) of this re-
port. This section summarizes rather than interprets data reviewed.
Introduction
Efficacy tests are intended to determine a product's ability to actually
control a specified target pest or produce a specified plant action. Data
on actual usefulness is also evaluated since the effectiveness and usefulness
of a given herbicide can differ. A herbicide can be effective in controlling
a target weed species, but some adverse effect such as .the death of desirable
plants would negate its usefulness.
The following criteria were used to review efficacy tests: types of
crops involved, target pests and population level, quantitative and qualitative
changes in yields, and rates and time of application in accordance with con-
ditions on the product's label. Data on higher dosages than recommended was
also reviewed to allow an estimate of the margin of safety between effective
pesticide levels and those which injure the crop. Some of these factors are
crop; variety; geographical location of the test; year of the test; methods
of application; numbers of sampling replicates; climatic conditions prior to
treatment, at treatment, and right after treatment; edaphic (soil) factors;
and many others. Statistical validity of tests was also considered.
This review presents a range of the potential benefits to be derived from
the use of cacodylic acid for weed control of specific pests in a specific
crop area.
Cacodylic acid is a broad spectrum herbicide used for postemergent weed
control. It is nonselective and produces top kill only; repeat applications
are required for seasonal weed control. It is often applied for control of
weeds along drainage ditchbanks and rights-of-way. It is also used for weed
control in nonbearing citrus orchards. Cacodylic acid is used as a harvest aid
for the defoliation of dryland and irrigated cotton with aerial or ground ap-
plication equipment. It is applied when 50% of the bolls are open and 7 to
10 days prior to anticipated picking. Conifer and hardwood trees are cont-
trolled by use of cacodylic acid which kills the crown when applied to the
tree. It is used by professional foresters and entomologists to control sev-
eral species of tree beetles.
An extensive literature review produced little information on the efficacy
of cacodylic acid used on cotton, citrus or specific grasses. Some references
reported the efficacy of mixtures of cacodylic acid and other herbicide combi-
nations .
124
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Efficacy of Pest Control
Weed Control - The results of efficacy tests on specific weed varieties show
mixed results. Sckerl et al. (1966) evaluated several herbicides for control
of Johnson grass, other grasses and broadleaf weeds along a highway right-of-
way in Arkansas. Cacodylic acid was applied at the rate of 3 Ib/acre 4 times
during the 1964 growing season when the Johnson grass was approximately 12 inches
in height. The results showed that the cacodylic acid treated plots had only
slightly fewer weeds and grasses than an untreated check plot. The authors
concluded that the treated plots were not significantly different from the
untreated check.
Arnold and Aitken (1973) evaluated several herbicides for Control of
bahiagrass in Florida pecan orchards. Since most of these orchards are sodded
and require mowing, growers^are becoming interested in chemical grass control.
Tests were conducted at Quincy, Florida, in 1972. Cacodylic acid was applied
at a rate of 8.0 Ib/acre in August. The results showed that it gave good
initial knockdown, but failed to provide total control. The ratings (on the
basis: 1 = no control; 10 = complete control) declined from 8.6, 2 weeks after
application to 3.0, 15 weeks after application. Similar results occurred when
an application of a mixture of 4.5 Ib monosodium methylarsenate and 2.0 Ib
cacodylic acid were applied.
Lange et al. (1969) evaluated several herbicides for weed control in non-
bearing citrus orchards containing Troyer citrange, trifoliate orange, Cleopatra
mandarin and Citrus macrophylla liners (seedlings) in selected California
counties between 1964 and 1968. The weeds included bindweed and a variety of
annual weeds. Cacodylic acid applications were made at 4 and 16 Ib/acre. At
both of these rates, 100% control was evident 1 month after application. No
other applications were made since the cacodylic acid was the most toxic
herbicide to the Troyer citrange liners. The growth of the liners as measured
by visual rating was about .the same as the weeded check when cacodylic acid was
applied at the 4 Ib/acre rate but was much slower at the 16 Ib/acre rate.
Cacodylic acid is often mixed with other herbicides. Bowmer and McCully
(1969) conducted a 2-yr study on Texas roadsides for control of weeds with
selected herbicide mixtures. Cacodylic acid mixed with another herbicide was
comparable to other herbicide mixtures in initial control and superior to most
in residual control. Treatments in June gave up to 75% control in October and
up to 68% control in the following May. Treatments with the cacodylic acid
mixtures resulted in superior total vegetation control.
Hardwood Tree Control - Cacodylic acid is used as a tool in forest management
to thin trees. Single tree injection with the herbicide has been shown to be
effective in controlling undesirable hardwoods. Smith (1965) injected several
species of trees with cacodylic acid and reported 100% kill of the crowns of
quaking aspen, red maple and paper birch, 3 weeks after injection. Tests on
Jack pine resulted in 100% crown kill 2 months after injection.
125
-------
Peevy (1969) evaluated several herbicides for control of blackjack oak
and mockernut hickory. Dosage rates of cacodylic acid were varied from 2 to 4 ml
from a. solution containing 5.7 Ib Al/gal. The acid was very effective against
the oak, causing from'96 to 100% kill of top growth. Hickory was difficult to
control. The results varied from 14 to 41% kill of the top growth.
Wiant and Walker (1969) evaluated cacodylic acid for precommercial thinning
of loblolly pines. Tests were conducted in the Stephen F. Austin Experimental
Forest near Nacogdoches, Texas, in 1969. Although 96% of the trees showed some
crown kill after 3 weeks, the proportion of trees that were completely dead
2 yr later varied from 0 to 35%. The rate of kill increased with dosage of
the herbicide.
Wiant and Walker (1969) also evaluated 30% cacodylic acid for control of
white oak, post oak, southern red oak, blackgum, sweetgum and hickory. The
average kill rate after 2 yr varied with the method of application and rate
of herbicide. Kill rates as high as 89% of the crown and 72% of the roots were
achieved. Blackgum and hickory were the most kill-resistant of the species
tested.
The authors concluded that cacodylic acid in adequate dosages may be used
to thin pines. Better hardwood kills are obtained when cacodylic acid silvicides
are applied in frills rather than in bore holes.
Application of the herbicide has been difficult—particularly in assuring
the proper injection into the tree. The development of the Hypo-Hatchet®has
allowed foresters to inject the proper amount of herbicide automatically and to
increase the speed of injection.
Hold and Voeller (1972) injected post oak trees in Oklahoma with 5.7 Ib AI/
gal cacodylic acid using the Hypo-HatchetxX, The authors concluded that cacodylic
acid did not give good control and recovery was quite pronounced after two
growing seasons. The percent defoliation declined from a mean of 61%, 7 months
after application, to 56% after 22 months.
Somewhat better results were obtained by the authors on post oak and hickory
during tests in Arkansas. Cacodylic acid gave extremely good initial control
with the post oak, but the oaks consistently recovered as the season progressed.
Good initial results were also observed on the hickory, but recovery was much
faster. The authors also concluded that the degree of control with the Hypo-Hatchet
is the same as with tubular injectors; however, it is 2 to 3 times more efficient
due to lower labor costs.
Voeller and Holt (1973) conducted further tests in 1971 and 1972 in Arkansas.
Cacodylic acid gave good initial control, but by the following year profuse
sprouting had developed. Tests on eastern red cedar showed poor control.
Tree Insect Control - Cacodylic acid has been evaluated for control of various
insects that attack trees. Among these are bark beetles, spruce beetles, the
Arizona 5-spined engraver, the round-headed pine beetle and the southern pine
beetle.
126
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Chansler and Pierce (1966) evaluated cacodylic acid for control of 5 types
of bark beetles in New Mexico forests. The results showed that in trees
injected with cacodylic acid (1) nearly all parent adults died before completing
egg galleries, (2) some eggs failed to hatch, and (3) high brood mortality occured.
The reduction in beetles ranged from 84 to 99%.
Stelzer (1970) evaluated cacodylic acid for control of the Arizona 5-spined
engraver in green ponderosa pines located in the Prescott National Forest in
Arizona. The Arizona 5-spined engraver readily attacked ponderosa pine trees
that had been poisoned with a fast-acting herbicide containing cacodylic acid.
The density of live brood, however, was reduced about 70% in trees treated from
April to July, as compared with the density in untreated trees felled during
the same period.
Trees poisoned from late July through August attracted more attacks than
those poisoned at any other time of the year. Trees felled about 1 month after
being poisoned in July were more effective as toxic trap trees than poisoned
trees left standing; the density of attack and mortality of the brood and parent
adults were appreciably greater in the felled trees. The treated trees evidently
dried out rapidly, trapping the adults and preventing brood development.
Ninety percent of the August-treated trees were attacked within 1 month
after treatment. This period coincided with the major flight of the beetle.
Attack densities and subsequent mortality were extremely high—brood mortality
was 100% and adult mortality about 60% in galleries situated on the upper bole.
During the fall, the lower bole of the trees attracted mass attacks by adults
that constructed hibernation-type galleries, but beetle mortality averaged 96%.
The round-headed pine beetle periodically causes significant mortality of
pole-sized ponderosa pine in the Southwest. Buffam and Flake (1971) reported
that these insects infested 100,000 acres in the Lincoln National Forest in
1969 killing up to 44 trees per acre in some areas. The authors achieved 100%
reduction of the round-headed pine beetles when the trees were frilled with a
hand hatchet and injected with cacodylic acid. Beetle mortality in power saw-
frilled trees was significantly less than in hatchet-frilled trees.
Copony and Morris (1971) baited loblolly pine trees with Frontalure
attractant to attract the southern pine beetle to cacodylicl acid trap trees.
All trap trees were poisoned with 1.2 ml of cacodylic acid applied to a shallow
frill of overlapping ax cuts.
The Frontalure-cacodylic acid treatments appeared almost totally successful
in controlling the spring populations of the southern pine beetle during epide-
mic conditions, where all trees within 15 ft of a baited trap tree were treated
with cacodylic acid. The authors concluded that if treatments had been made
earlier in the spring (2 to 4 weeks before beetle emergence), the results might
have been more successful. Baited trap trees would then have been available
for the earliest emerging beetles, and the trap trees would have had more time
to accept the cacodylic acid poison, thus creating conditions less favorable to
beetle development.
127
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However, the Forest Service does not recommend the use of cacodylic acid
combined with the pheromone, Frontalure. Some doubts exist as to whether
cacodylic acid is translocated in the southern pine to provide control of the
southern pine beetle. Consequently, it is more customary to control the
southern pine beetle with the older method of salvaging attacked trees combined
with piling and burning refuse.
The spruce beetle is the most serious pest of the Englemann spruce in the
United States. Buffam and Yasinski (1971) used a hand ax to frill trees in the
Carson National Forest in New Mexico. Cacodylic acid was applied to the trough
and the trees felled 30 days after treatment. The authors reported that the
method was successful in eliminating the hazard of spruce beetle buildup. Only
20 live larvae were found in all samples taken from 45 felled trees.
Frye and Wygant (1971) also evaluated cacodylic acid for treatment of the
spruce beetle in Englemann spruce. The results showed that mortality rates of
were achieved.
Buffam (1971) added cacodylic acid to Englemann spruce trees in an effort
to produce lethal traps for the spruce beetle and found that trees treated in
mid-June and felled 2 weeks later had approximately the same number of attacks
as check trees. However, only a few live spruce beetle larvae and pupae were
found in samples from trees treated at this time whereas significant numbers
were found in samples from check trees.
128
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References
Arnold, C. E., and J. B. Aitken, "Perennial Grass Control in Pecan Orchards,"
Proceedings of the Southern Weed Science Society. 26:231-235 (1973).
Bowmer, W. J., and W. G. McCully, "Screening Soil Sterilants for Use on
Roadsides," Proceedings of the Southern Weed Science Society, 22:293-300
(1969).
Buffaip, P. E., "Spruce Beetle Suppression in Trap Trees Treated with Cacodylic
Acid." J. Econ. Entomol.. 64:958-960 (1971).
Buffam, P. E., and H. W. Flake, Jr., "Roundheaded Pine Beetle Mortality in
Cacodylic Acid-Treated Trees," J. Econ. Entomol., 64:969-970 (1971).
Buffam, P. E., and F. M. Yasinski, "Spruce Beetle Hazard Reduction with
Cacodylic Acid," J. Econ. Entomol., 64:751-752 (1971).
Chansler, J. F., and D. A. Pierce, "Bark Beetle Mortality in Trees Injected
with Cacodylic Acid- (Herbicide)," J. Econ. Entomol.. 59:1357-1359 (1966).
Copony, J. A., and C. L. Morris, "Southern Pine Beetle Suppression with
Frontalure and Cacodylic Acid Treatments," J. Econ. Entomol^, 64:911-916 (1971)
Dalton, R. L., "Chemical Brush Control Offers the Best Economics for the
Potomac Edison Company," Northeast Weed Conference Proceedings, 21:428-
433 (1967).
Frye, R. H., and N. D. Wygant, "Spruce-Beetle Mortality in Cacodylic Acid-
Treated Englemann Spruce Trap Trees," J. Econ. Entomol., 64:911-916 (1971).
Headley, J. C., and J. N. Lewis, "The Pesticide Problem: An Economic Approach
to Public Policy," Resources for the Future, Inc., Washington, D.C. (1967).
Holt, H. A. and J. E. Voeller, "Hardwood Control Trials with the Hypo-Hatchet®"
Proceedings of the Southern Weed Science Society. 25:270-276 (1972).
Lange, A. H., B. B. Fischer, and G. Suthers, "Weed Control in Non-bearing
Citrus," California Agriculture (July 1969).
McHenry, W. B., and P. S. Parsons, "Cost of Controllign Canalbank Weeds by
Water Agencies," California Weed Conference Proceeding, 19:38-41 (1967).
Offutt, J. R., "Chemical Weed Control Replaces Mechanical Weed Control in
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