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OCR for page 117
Biologic Effects
of Arsenic on
Plants and Animals
Arsenic has long held a position of ambiguity with regard to its activity
in biologic systems. In spite of the recognized toxicity of many forms of
arsenic, various arsenicals have been used in the practice of medicine.
A specific nutritional role for inorganic arsenic has been uncovered
only recently, but animal feeds have been supplemented with
"growth-promoting" organic arsenical additives for many years.
Another curious feature of arsenic biochemistry is the ability of the
element partially to counteract the ill effects of yet another toxic
substance, selenium. This chapter summarizes what is known about
the detrimental and beneficial effects of arsenic on living systems other
than man and discusses in as much detail as appropriate the molecular
mechanisms responsible for these effects. Previous reviews have dealt
with the toxicology, i09 general biochemistry 8~4 8~5 and pharmacology
of arsenic.
MICROORGANISMS
Toxicity
The state of knowledge regarding the effects of arsenic on microor-
ganisms was summarized very well in a study by Mandel et al.5~7 on the
117
OCR for page 118
118
ARSENIC
action of arsenic on Bacillus cereus. Trivalent sodium arsenite was
found to inhibit growth at a lower concentration (0.4 mM) than penta-
valent sodium arsenate (10 rnM). The toxicity of the arsenate could be
increased by lowering the phosphate concentration of the growth
medium, whereas the inhibitory effect of arsenite was independent of
phosphate concentration. This inverse relationship between the toxic-
ity of arsenate and the concentration of phosphate might be related to
the fact that arsenate can compete with phosphate for transport.
However, Da Costai93 found that phosphate could suppress the inhibi-
tory effects of arsenite, as well as arsenate, on the growth of fungi.
Mandel et al.5~7 showed that neither arsenate nor arsenite produced
any specific effects in B. cereus on the incorporation of radioactive
precursors into ribonucleic and deoxyribonucleic acids, proteins, or
cell wall. Radioarsenite was bound by the microorganism much more
strongly than radioarsenate, in agreement with the hypothesis that the
toxicity of a particular arsenical was related to the binding of it to the
tissues.358 Because no instance of interconversion between As(V) and
As(III) could be established, it was concluded that the two compounds
inhibited the growth of B. cereus by separate mechanisms. The mecha-
nisms of toxicity of arsenicals for this organism seem to be similar to
those proposed for mammalian systems, which are discussed later.
Adaptation
The adaptation of microorganisms to arsenic compounds was of great
practical interest during the earlier part of this century, because
organic arsenicals were used extensively as trypanocides at that time.
The resistance to organic arsenicals was found to depend on the nature
of the chemical substituents on the phenyl ring:5 water-attracting
groups (such as -OH and -NH2), less hydrophilic groups (such as
-CH3 and -NO2), and groups highly ionized at a pH of 7 (such as
-COOH). The state of oxidation of the arsenic is of little consequence
in inducing resistance to any of these compounds. The mechanism of
drug resistance in trypanosomes is usually a decreased permeability to
the drug, and the nonarsenical portion of the molecule largely deter-
mines the uptake of the drug by the parasite.
A decreased permeability to arsenic appears to be a rather wide-
spread adaptational mechanism, in that a decreased arsenic uptake was
observed in Escherichia cold mutants that were resistant to arsenate70
and in Pseudomonas pseudomallei that had adapted to arsenite.25 In
the latter case, no increase in the content of a-ketoglutarate dehydro-
genase, total sulfhydryl compounds, or lipoic acid was observed in the
OCR for page 119
Biologic Effects of Arsenic on Plants and Animals
119
resistant bacteria.72 That the total quantity of free thiol groups may be
important in some cases of arsenic tolerance, however, was suggested
by the work of Harington,327 who found that resistant strains of the blue
tick contained more total sulfhydryl than sensitive strains.
Novick and Roth59i showed that the penicillinase plasmids, a series
of extrachromosomal resistance factors in Staphylococcus aureus,
carry determinants of resistance to several inorganic ions, as well as
resistance to penicillin. Among the inorganic ions were arsenite, arse-
nate, lead, cadmium, and mercury. Resistance to arsenate was found to
be induced in cultures of plasmid-positive strains by prior growth with
an uninhibitory concentration of the anion. Dyke et al.225 observed that
strains resistant to arsenate, mercury, and cadmium were nearly al-
ways resistant to multiple antibiotics and produced large amounts of
penicillinase. Although the general genetic and physiologic properties
of these ion-resistance markers have been studied, hardly any work has
been done on the biochemical mechanisms of this sensitivity and
resistance.
PLANTS
Arsenic occurs in all soils and natural waters; thus, plants have
obviously evolved in the presence of arsenic ions. It could therefore
well be that arsenic is an essential element for plant growth, but it has
not been proved. There are no well-authenticated beneficial effects of
arsenic on plants. Arsenic is chemically similar to phosphorus, an
essential plant nutrient. That it can substitute for phosphorus in plant
nutrition, however, is doubtful; in some soils, the application of
phosphate fertilizer increases arsenic toxicity (through the release of
fixed arsenic).7~5 Other interactions between arsenic and plant nu-
trients are treated later.
Biochemical Response to Arsenic Compounds
When arsenic in solution penetrates the cuticle and enters the apoplast
system (the nonliving cell-wall phase), it bathes the external surface of
the plasmolemma of the symplast. This is the location of at least some
of the enzymes of the living plant. One of the first symptoms of injury
by sodium arsenite is wilting, caused by loss of turgor, and this
immediately suggests an alteration in membrane integrity. Reaction of
trivalent arsenic with sulfhydryl enzymes could well explain the effects
of membrane degradation injury and eventually death.
OCR for page 120
120
ARSENIC
In general, arsenates are less toxic than arsenites. The arsenate
symptoms involve chlorosis, but not rapid loss of turgor (at least in the
early expression of toxicity), and the contact action of the arsenates is
more subtle. Arsenate is known to uncouple phosphorylation. Thus,
the coupled phosphorylation of adenosine diphosphate (ADP) iS
abolished, the energy of adenosine triphosphate (ATP) iS not available,
and the plant must slowly succumb.207
Arsenate has other profound effects on plant systems. For example,
Figure 5-1 shows the relative effects of arsenite and arsenate on the
activation of the enzyme fumarase. Fumaric acid is a constituent of all
plants and is involved in the citric acid cycle. Fumarase carries out the
conversion of fumarate to ~-malate.
The above examples typify the role played by the organic arsenical
herbicides in plant metabolism. When one considers the number of
reactions in plants that involve sulfhydryl groups and phosphorus, it is
easy to appreciate the ways in which arsenites and arsenates may upset
plant metabolism and interfere with normal growth. The ability of
arsenate to enter into reactions in place of phosphate is probably the
most important way in which arsenic acts as a toxicant. Not only does
it substitute for phosphate in a number of ways, but work with labeled
arsenates and arsenates has indicated that these compounds are ab-
sorbed and translocated much as phosphates are. It is difficult to
visualize a more effective way in which an herbicide might kill a plant.
Phytotoxicity of Organic Arsenicals
Injury symptoms on crop plants resulting from toxic quantities of
arsenic in soils were noted in the 1930's, when it was found that young
trees planted in old orchard soils grew slowly and were stunted.748
Young apple trees, in addition to being stunted, had leaf symptoms that
indicated water-deficiency stress, which implied injury to the roots;
pears showed similar symptoms.785
Peach trees planted on these old orchard soils that have accumulated
lead arsenate exhibit by midsummer a red or brown discoloration along
the leaf margins and then throughout the leaves. The discolored tissues
die and drop out, giving the leaves a shot-hole appearance. Defoliation
also occurs and may be complete by late summer. The injury appears
first in the older leaves; young leaves on shoot tips may remain normal.
Yields of fruit may be reduced, and the trees are usually stunted.
Thompson and Batjer785 performed experiments aimed at correcting
arsenic injury to peach trees. They found correlations between shot-
holing and defoliation and between leaf arsenic content and defoliation;
OCR for page 121
Biologic Effects of Arsenic on Plants and Animals
c'
o
>
f
6
7
\ Arser.ate
Arsenite
8
pH
9
FIGURE 5-1 Velocity of activation of fumarase by arsenate and
arsenite ions as a function of pH. Adapted from Dixon and
Webb, 207 (p. 473)
121
arsenic content varied between 1 and 4 ppm. They found that zinc
sulfate applied at 10 lb (4.5 kg) per tree reduced defoliation; nitrogen
application at 1.4 lb (0.6 kg) per tree also reduced defoliation; a combi-
nation of these two treatments reduced defoliation that had been as
high as 81% to around 2-3%, and even eliminated it in some orchards.
Repeat treatments with zinc in later years had little or no effect, but
maintaining a high nitrogen content reduced defoliation at later years.
Lindner and Reeves473 explained that arsenic injury was confused
with western X-disease, which is caused by a virus. They described the
symptoms of the viral disease and arsenic toxicity; both cause shot-
holing and defoliation, but arsenic-affected trees have greener leaves,
and X-disease causes some chlorosis. Leaves that showed arsenic
injury symptoms contained arsenic at 2.1-8.2 ppm; normal leaves,
0.9-1.7 ppm. Viral-diseased trees may produce deformed fruits, which
drop prematurely; fruits of arsenic-affected trees are of normal form
OCR for page 122
122
ARSENIC
and remain on the tree for the normal period. Arsenic analyses of
leaves provide the most accurate diagnosis.
Woolson873 studied the uptake and phytotoxicity of arsenic in six
vegetable crops grown in a greenhouse. Sodium arsenate was mixed
into three soil types; after moistening, the cultures were left for a
month for the arsenic to come to equilibrium. Sensitivity to the arsenic
decreased in the following order: green beans, lima beans, spinach,
cabbages, tomatoes, and radishes. All crops were fertilized at ra as
indicated by standardized soil tests and crop needs. The yields indi-
cated that arsenic was generally most phytotoxic in the Lakeland soil;
no plants grew when the arsenic concentration was 500 ppm. At 10, 50,
and 100 ppm, crops survived; growth was proportional to arsenic
concentration. The amount of available arsenic in some treatments
continued to change throughout the 19-month experimental period;
some of the change may have been the result of the addition of
phosphate fertilizers, particularly where available arsenic reached a
minimum and then increased. Plant growth at any particular degree of
available arsenic in the soil may be affected by the amount of available
phosphorus in the soil solution.878
The organoarsenical herbicides are not growth-regulators in the way
that plant hormones are; they apparently act through or on enzyme
systems to inhibit growth. They kill relatively slowly; the first
symptoms are usually chlorosis, cessation of growth, and gradual
browning, and dehydration and death follow. Rhizomes and tubers
may show browning of the storage tissues; buds fail to sprout, and the
whole structure eventually decomposes. Cotton plants treated by
directed spraying with MSMA show retarded growth from which they
may recover.447
When resprouting of tubers or rhizomes does occur, treatment
should be repeated when some of the leaves have reached full size;
treatment before then will not result in translocation, because move-
ment of the assimilate stream into the underground organs is necessary
to carry the toxicant to the proper sites of action.
Rumberg et al.692 reported DsMA-induced loss of chlorophyll in
crabgrass within 2-3 days of treatment at 75 or 85 F (24 or 29 C),
but it was hardly noticeable after 5 days at 60 F (16 C); the results are
summarized in Table 5-1.
Others have observed symptoms on various annual plants, but few
detailed descriptions are noted in the literature. Many annual weeds
are ultimately desiccated and become necrotic after treatment. Re-
growth from axillary buds is usually chlorotic. Cotton and other plants
OCR for page 123
Biologic Effects of Arsenic on Plants and Animals
TABLE 5-1 Effect of Temperature after Treatment on the Degree
of Chlorosis Induced by DSMA in Crabgrassa
Chlorosis Ratingb
DSMA 60 F (16 C) 75 F (24 C) 85 F (29 C)
123
lb/acre kg/ha 5 Days 10 Days 5 Days 10 Days 5 Days 10 Days
2 2.2 0.2 2.7 3.2 2.2 1.8 2.0
6 6.7 0.2 3.3 6.8 6.0 5.1 7.1
18 20.2 0.3 2.7 7.1 7.1 5.4 7.6
Mean 0.2 2.9 5.7 5.1 4.1 5.6
aDenved from Rumberg et al.693
bA scale of 0-10: 0 = no chlorosis; 10 = complete chlorosis.
become deeply pigmented (red) in the stem and petiole and even the
leaves, if the arsenicals are applied in sublethal dosages.
On perennials, such as Johnsongrass, chlorosis does not develop
before necrosis on sprayed foliage, but regrowth usually is chlorotic for
some period.4~9 On purple nutsedge (Cyperus rotundus), Holt et al.366
described symptoms as "a chlorotic appearance which starts at the leaf
base and progresses toward the leaf tip until the entire leaf is chlorotic"
and as "first visible four days after the initial applications of AMA."
On hardstem bulrush (Scirpus acutus), an aquatic species, stems
became chlorotic; necrosis proceeded from the tip concurrently with
development of a tan discoloration over the length of the stem; after a
month, the entire stem became brown and collapsed.4~8 Stems regrow-
ing from the bulrush rhizome were chlorotic with necrotic tips and
usually died.
Lange450 studied MSMA toxicity symptoms on stone fruits by spray-
ing MSMA at 4 and 16 lb/acre (4.5 and 17.9 kg/ha) on the bottom
one-third of the foliage. He observed a spotty chlorosis of the leaf,
followed by necrosis of all or part of the leaf and often defoliation.
Untreated upper leaves and new growth showed symptoms of injury
that indicated movement of the toxic material to the untreated area.
Many factors could affect response; they include herbicide applica-
tion rate and formulation, surfactant, timing, volume of carrier, quality
of diluent, pH, timing of evaluation, ecotypes, senescence, stage of
growth, dormant-season disturbance of root systems before treatment,
fertility, moisture availability and continuity, plant competition, tem-
perature, light intensity, and insect and mechanical wounding of foliage
OCR for page 124
124
ARSENIC
before treatment. Any of these can have a dominant effect on the
response.
Several researchers who have studied methanearsonates have re-
ported temperature-inf~uenced results. Sckerl et al.,7~9 Kempen et
al.,4~9 Laurin and Dever,454 Riepma,669 and Bounds90 all mentioned that
toxicity was greater at higher temperatures. Toxicity was less on
Johnsongrass in regions of California influenced by cool marine air,
and higher rates of application were required than in hotter regions.
One controlled-environment study of Rumberg et al. 6',3 indicated that
chlorosis occurred considerably earlier in crabgrass at higher tempera-
ture (24 or 29 C, versus 16 C), and injury, as measured by dry weight
after 10 days, was greater at higher temperature. With sodium arsenite
and cacodylic acid, temperature had no effect.
Kempen4~7 found that relatively high temperature (35 C) and light
t2,800 ft-c (30,140 lx)] increased the necrosis of Johnsongrass foliage
and the kill of the rhizomes, compared with low temperature (15 C)
and light L320 ft-c (3,445 led. He found that only 1 day was required for
So-so necrosis of the foliage at the higher temperature and light, but 12
days at the lower temperature and light. McWhorter=~3r, and Kempen et
al.4~9 suggested that droughtiness after application increased weed
control.
In studies on the effects of AMA on food reserves in purple nutsedge,
Duble and Holt2'3 found, by tracer experiments and chemical analysis,
that starch disappeared and arsenic increased in tubers of plants that
were given repeated applications of the herbicide. In general, AMA-
treated plants had a higher rate of utilization of the products of
photosynthesis than untreated plants. Apparently, carbohydrates were
utilized in preference to fats and proteins.
From the results of Woolson et al., it is evident that total arsenic in a
soil is not correlated with phytotoxicity; correlation between plant
growth and available arsenic is better. 876 Some soils can remove
arsenic from the soil solution more rapidly and more completely than
other soils by fixation on soil colloids. In these experiments
Hagerstown soil removed 2-5 times more arsenic than did the other
two soils. Woolson et al. concluded that the large amount of available
arsenic in the Christiana soil may have resulted from the high phos-
phorus content, which prevented formation of insoluble iron arsenates
through competition for reaction sites on the surface of soil particles.
Also involved is the larger amount of available aluminum in the
Hagerstown soil. Woolson, Axley, and Kearney877 have shown that, at
high arsenic concentration in some soils, aluminum is more important
than iron in removing arsenic from the soil solution.
OCR for page 125
Biologic Effects of Arsenic on Plants and Animals
125
Arle and Hamilton26 found that topical applications of MSMA affected
growth of cotton more than applications of DSMA. There were usually no
deleterious effects of single treatments with DSMA; single applications
of MSMA later and at higher rates reduced yields. Repeated treatments
with MSMA reduced yields more than DSMA treatments.
Keeley and Thullen4~4 studied the responses of cotton plants to
topical applications of MSMA, DSMA, and MAA at 13, 20, and 3 1 C.
DSMA proved to be less injurious to young cotton plants than MSMA.
Injury by MSMA was severe at 13 C, intermediate at 20 C, and low at
31 C, and inclusion of 0.4~o surfactant with the MSMA increased the
injury. Injury by DSMA was intermediate at 13 C, low at 20 C, and
lacking at 31 C, and inclusion of surfactant in the spray solution
increased injury only slightly.
Cotyledons of cotton seedlings absorbed F14C]MAA and L14C]DSMA.
The MSMA solution in these experiments was adjusted to a pH of 6.4,
and the DSMA to a pH of 10.4. Autoradiographs of cotton plants treated
with ~4C-labeled MSMA, MAA, and DSMA showed evidence of greatest
absorption and translocation of MSMA at 13 C, slight translocation at
20 C, and no translocation at 29 C. Very little FI4C]MAA or t~4C]DsMA
was translocated. These results are contrary to the generalization for
translocation of assimilates and other tracers, which normally penetrate
and move more readily at high temperatures. (Rumberg et al. 693 found
chlorosis from DSMA treatment and the translocation of DSMA to in-
crease with temperature.)
Interactions between Arsenicals and Nutrients
Several studies have been conducted on interactions between phos-
phorus and arsenic in soils and nutrient solutions. Because these two
elements have somewhat similar chemical characteristics, substitution
of arsenic for phosphorus might occur in plant metabolic products.
Rate trials in soil and nutrient solutions, however, have yielded con
flicting results, partially because available phosphorus and arsenic
concentrations have not generally been determined.
Schweizer7~5 showed that high phosphorus content increased the
toxicity of DSMA to cotton, but there was considerable variation
between the two soil types tested.
~ ittle is known of interactions between arsenic and phosphorus in
plants. Everett '39 indicated that phosphorus increased the arsenic
content of bluegrass in a turf treated with tricalcium arsenate. How-
ever, he found that phosphorus reduced absorption of tricalcium
arsenate (measured as arsenic) from nutrient solutions from 246 to 29
. . _
OCR for page 126
126
ARSENIC
ppm. He stated that phosphorus at 100 ppm reduced the soluble arsenic
in the nutrient solution from 15.8 ppm to 2.6 ppm. This might account
for the lack of increase in arsenic uptake with high phosphorus in
nutrient solutions. Everett also indicated that crabgrass absorbed twice
as much tricalcium arsenate as did bluegrass; this suggests a species
difference. Sckerl,7~6 in his review of the literature, indicated that
phosphorus reduced arsenic toxicity.
Webb843 suggested that arsenates inhibit various phosphatase en-
zymes about as potently as phosphate and probably combine with the
enzymes in a similar manner. Sckerl7~6 related that arsenate competes
with phosphorus for uptake and transport in the cell.
That arsenicals might interact with zinc was indicated by work of
Batjer and Bensons5 and Martin (personal communication, 19681.
Batjer and Benson showed that toxicity in peaches (but not apples)
grown in arsenic-contaminated soils could be reduced by foliar applica-
tions of zinc or iron chelates or soil applications of zinc or iron
sulfates.55 Zinc chelates worked best and reduced the symptoms and
the arsenic content of peach leaves. Martin related that orchardists in
the northwestern United States use zinc sulfate at 5 lb (2.3 kg) per tree
plus generous amounts of ammonium sulfate when starting peach trees
in high-arsenic soils.
Burleson and Paged did root studies with flax that indicated that,
with absorption of more than optimal phosphorus, phosphorus and zinc
reacted together in a manner that reduced either their mobility or their
solubility. Sharma et al.722 showed that translocation of zinc to shoots
was inhibited by high soil phosphorus.
Krantz and Brown438 published a list of zinc- and iron-sensitive
plants; there was no obvious correlation between symptoms of defi-
ciency and susceptibility to methanearsonate sprays.
Mode of Action
Considering the overall action of arsenites as herbicides, it seems
important that they are able to penetrate the cuticle and enter into the
apoplast phase of the plant system. Here, they may move with transpi-
ration water and bathe the cells of the foliar organs to- which they have
been applied. At low concentration, it seems possible that arsenites are
absorbed into the symplast and then translocated for at least short
distances. Under most conditions in which these compounds have been
used in the field, their concentrations have been such that rapid contact
injury has precluded extensive translocation. This is related at least
partly to their rapid effect in membrane degradation.
OCR for page 127
Biologic Effects of Arsenic on Plants and Animals
127
The arsenates, in contrast, have much lower contact toxicity; they
are absorbed and translocated, at least in species that have succumbed
to treatment, such as Johnsongrass and nutsedge. In susceptible pe-
rennial weeds, the great virtue of MSMA and DSMA has been their ability
to penetrate into and destroy underground tubers and rhizomes. Thus,
with a few repeated applications, these arsenicals have controlled two
of the most serious perennial weed species species that have resisted
control by any other means.
As topical sprays, these compounds are inactivated almost instan-
taneously on contact with the soil and therefore may be used with
impunity in many row crops; cotton is one of the more important of
these. Although arsenicals in ordinary herbicidaI dosages are rapidly
rendered unavailable to plants in the soil, and although most soils have
a very great capacity to inactivate and hold arsenic, arsenic residues in
soils may eventually become troublesome. For this reason, in any
weed control activity involving arsenical herbicides, integrated pro-
grams of herbicide rotation should be used. If such programs are used,
occasional application of the organic arsenicals in the particular roles in
which they are highly effective may not result in soil residues of any
. ·~
slgn~lcance.
As for the chemical mechanisms by which the organic arsenates kill
plants, their relatively slow action involving translocation and produc-
ing chlorosis as a primary symptom seems to implicate disturbance of
phosphorus metabolism. Not only are they absorbed and translocated
in plants much as are phosphates, but also they affect many organelles
in the cells, including the chloroplasts, in all of which phosphorus plays
important roles.35
This interpretation is further strengthened by evidence of
Schweizer7~5 that the addition of phosphorus to two silt-loam soils
increased the toxicity of DSMA to cotton, possibly by saturating sites in
these soils on which both arsenate and phosphate are fixed. As early as
1934, Albert6 reported that residues of calcium arsenate became more
toxic to several crops where phosphate fertilizer was applied heavily.
There is substantial evidence that phosphates and arsenates tend to
replace each other chemically, but that arsenic cannot serve the many
essential roles of phosphorus in plants.
The uncoupling of oxidative phosphorylation and the formation of
complexes with sulfhydryl-containing enzymes may also enter the
picture of arsenic phytotoxicity. However, trivalent arsenic is the form
commonly associated with these effects, and this would implicate
arsenites, rather than arsenates or arsenates.
OCR for page 162
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OCR for page 166
66
ARSENIC
trioxide-poisoned grasshoppers containing arsenic at up to 910 ppm as
a dry meal. Lilly470 fed grasshopper bait containing sodium arsenite or
freshly poisoned grasshoppers to ring-necked pheasants without ap-
parent ill effect. One bird consumed over 2,500 poisoned grasshoppers
(approximately 8 mg of arsenic) in a 20-day period and, after a 7-day
rest period, was sacrificed and analyzed for arsenic (Table 5-81. Little
accumulation of arsenic was observed. The author noted that pheas-
ants were reluctant to consume arsenic-containing baits, but readily
consumed poisoned grasshoppers. The results indicate that there was
little danger to this species from the grasshopper-poisoning activities.
Helminen342 also noted that spraying a potato field with an arsenical
insecticide had little effect on pheasants penned on this field.
Several studies conducted by Whitehead854 (Table 5-9) are ques-
tionable, although noteworthy because they are among the few that
involved songbirds. Arsenic trioxide was used to poison western grass-
hoppers (Melanophis bivittatus, M. femus-rubrum, M. bispinosus),
which were fed to bobwhite quail, mockingbirds (Mimus polyglottos),
robins (Turdus migratorious), meadowlarks (Sturnella magna),
redwing blackbirds (Agelaius phoeniceus), brown thrashers (Toxos-
toma radium), dickcissels (Spiza americana), orchard orioles (Icterus
spurius), scissortails (Muscivora forficata), and English sparrows
(Passer domesticus). The author noted that, when quail consumed the
maximal amount (25 g) of grasshoppers, less than lOYo of a toxic dose
was ingested; therefore, no detrimental effects were noted. Poisoned
grasshoppers were force-fed to the various nestling birds in the wild.
Many uncontrollable variables consequently also affected the outcome
of these experiments. The results showed that fairly large numbers of
poisoned grasshoppers (up to 134, containing a total of about 40 mg of
arsenic) could be fed to nestling songbirds without any noticeable toxic
effect. About 49~o of all the birds fed poisoned grasshoppers in this
experiment matured, compared with about 60~o of those fed un-
poisoned grasshoppers. Because there was great variability in these
data, no significant detrimental effects were attributed to the arsenic
consumption. Generally, the data indicated that songbirds experienced
little danger from the ingestion of this pesticide in the form of poisoned
grasshoppers.
Work undertaken at the Patuxent Wildlife Research Center698 to
evaluate the possible dangers of widespread use of copper acetoarse-
nite for mosquito control, particularly in southern marshes, indicated
that there is little hazard when this compound is applied at the
recommended rate of 0.75 lb/acre (0.84 kg/ha). Male cowbirds (Mola-
thrus ater) were poisoned only when fed copper acetoarsenite at about
OCR for page 167
Biologic Effects of Arsenic on Plants and Animals
167
225 ppm (arsenic at 100 ppm) in the diet (Table 5-7) for 3 months;
similar diets containing copper acetoarsenite at 25 and 75 ppm (arsenic
at 11 and 33 ppm) appeared to have no effect on mortality. Arsenic
residues (Table 5-8) were determined in birds that had died from
consuming diets containing arsenic at 100 ppm (W. H. Stickle, per-
sonal communication). Whole-body concentration reached a peak of
about 1.7 ppm (dry weight) in yearling male cowbirds after about 6
months of feeding arsenic at 11 ppm in the diet and thereafter appeared
to level off. Birds given arsenic at 33 ppm reached a maximal whole-
body concentration of about 6.6 ppm for the same period. Whole-body
arsenic content continued to rise at this dose, reaching 8.6 ppm at 7
months. The latter concentration approaches toxicity.
The herbicidal properties of arsenic made its use as a tree-debarker
an important factor in the northeastern U.S. wood pulp industry in the
1940's and 1950's. Cooki62 reported two cases in New York in which
about 10 white-tailed deer (Odocoileus virginianus) consumed fetal
amounts of sodium arsenite that was used to debark pulp trees. Field
studies by Boyce and Verme93 showed that 923-2,770 mg of arsenic (as
sodium arsenite) was lethal to deer when licked from the bark of
treated trees. No body weights were given, but, if we assume that one
of the poisoned deer (a yearling doe) weighed about 27 kg, then we can
calculate a minimal lethal dose of about 34 mg/kg. In a study to
determine the palatability or acceptability of sodium arsenite, potas-
sium arsenite, and ammonium arsenite to deer, the authors recorded
the number of licks that the test deer made on trees coated with
solutions of these compounds. They observed that sodium arsenite was
as palatable as sodium chloride, whereas potassium arsenite was
significantly less palatable, and ammonium arsenite was the least
acceptable to the deer. The authors also report that wildlife kills from
arsenic poisoning in Michigan's upper peninsula in 1952 amounted to
five deer, four porcupines, and one rabbit on about 200 acres (81 ha) of
commercially treated trees. In 1953 and 1954, apparently, only one
wildlife mortality was found in over 5,000 acres, or 2,023 ha (which
contained over 500 acres, or 202 ha, of treated trees), in lower Michi-
gan. The practice of debarking trees with arsenicals for commercial use
has been almost completely replaced by mechanical debarking equip-
ment.
A well-documented report of a wildlife killoff attributable to arsenic
was made by Swiggart et al.776 They reported the poisoning of 23
white-tailed deer in Tennessee by the apparent misuse of arsenic acid
as an herbicide to control Johnsongrass. The herbicide (USDA Reg.
295-6) was labeled for use in controlling crabgrass and Dallisgrass on
OCR for page 168
68
ARSENIC
Bermuda-grass lawns and was applied to a 600-acre (243-ha) field in
preparation for planting soybeans. A 5-gal mixture containing 0.5 gal of
arsenic acid was applied per acre (0.05 m3 of mixture containing
0.005 m3 of arsenic acid per hectare). The dead deer were all found on
the 600-acre field and appeared to have died on the same day. Appar-
ently, the toxicity of this herbicide dissipated in a few days, inasmuch
as no further mortalities were recorded. Autopsies showed that the
deer died of massive hemorrhagic gastroenteritis. Analyses performed
by the EPA Toxicology Laboratory showed that surface soil samples
contained arsenic at up to 2.4 ppm, whereas water samples from the
area averaged 0.42 ppm. Arsenic concentrations in the dead deer are
shown in Table 5-8. It is interesting that the farmer and cropduster
using the pesticide in this case were both taken to court by the
Tennessee Health Department and sued for damages. In an apparently
unprecedented decision, the defendants were made to pay for the
poisoned deer $109/head, the amount needed to transport new deer
into the area (W. D. Turner, personal communication).
In March 1974, another deer kill involving at least two white-tailed
deer was discovered in southwest Memphis and Shelby County, Ten-
nessee, by R. C. Swiggart and W. D. Turner (personal communica-
tion). Although these deer were found in an area that had been treated
with a cotton defoliant in the fall of 1973, the probable cause of death
was determined to be the contamination of the water in a runoff ditch
with MSMA. Several empty MSMA drums were found in the ditch, and
mixing apparatus was nearby. Tissue analyses of these deer (Table 5-8)
showed what are considered toxic concentrations of arsenic. This is in
agreement with the studies of Dickinson,~76 who showed that the concen-
trations of arsenic in the livers of cattle fed toxic doses of MSMA were
less than half those found in these dead deer. Analyses for chlorinated
pesticides and other heavy metals were performed, but none were
present in apparently toxic concentrations. As a point of perspective,
these deer were found on land cultivated by the same farmer referred to
by Swiggart et al.776 Although both reports can be related to misuse of
arsenicals, the Swiggart et al. report appears to refer to an instance in
which wildlife died from consuming contaminated herbage. It is there-
fore in contrast with other reports cited here that indicated little hazard
from the extensive use of some arsenic compounds. This is probably
because of the varying toxicity of the numerous arsenicals, as well as
the saturation effects of spraying huge acreages with arsenicals and
leaving little untreated foliage for the local wildlife population to
consume.
OCR for page 169
Biologic Effects of Arsenic on Plants and Animals
169
Little information is available on background or environmental con-
centrations of arsenic in various wild species. Bencko et al.,64 how-
ever, stated that rabbits reproduced normally when exposed to air from
a plant that discharged large amounts of arsenic for up to 12 months.
They observed significant although apparently nontoxic accumulations
of arsenic in the kidneys, hair, and nails of rabbits exposed for 9 and 12
months. Martin and Nickerson524 monitored starlings (Sturnus vul-
garis) from 50 sites in the United States during 1971; except for one
sample in Michigan, all contained arsenic (whole body) at 0.04 ppm or
less (Table 5-81. Similarly, Stickle (personal communication) found that
trapped yearling male cowbirds not exposed to arsenic had brain, liver,
kidney, muscle, and feather-skin concentrations of less than 0.78, less
than 0.41, less than 1.48, less than 0.19, and 0.13 ppm, respectively.
Andren et al. }7 have monitored the ecosystem of the Walker Branch
watershed in Tennessee for a number of trace elements, including
arsenic. Unfortunately, arsenic was determined by spark-source mass
spectrometry with a method that is only about 50~o accurate. The
quantitative validity of these data are therefore questionable, but the
trends observed are worth noting. Such animals as earthworms (19
ppm) and cryptozoa (100 ppm), which are close to the soil surface and
tree roots (11 ppm), contained high concentrations of arsenic. Simi-
larly, tree-canopy insects also had high arsenic contents (10 ppm). Arse-
nic was the only element studied, however, that showed any decline in
concentration with higher trophic levels. For example, fieldmice con-
tained arsenic at 1 ppm of the whole body, but owls, which consume
large quantities of mice, contained only 0.05 ppm (Table 5-81. It is
noteworthy that the hawk sample contained 8 times as much arsenic as
the owl, although one would expect that they consumed similar diets.
In 1969, a large dieoff of common auks guillemots (Uria allge),
razorbills (Alca torda), and puffins (Fratercula arctica) was observed
in the Irish Sea. Because the populations of these species of seabirds
have been declining in recent years, an extensive study360 of this dieoff
was undertaken by the Natural Environment Research Council of
Britain. These birds congregate in large groups in open water and
spend most of the year at sea, except during March and April, when
they gather at breeding grounds. It is significant that the killoff oc-
curred in the late summer and early fall, when the birds are flightless
because of molting. The dieoff period began in late July and ended in
mid-October, when a total count of over 12,000 dead birds was re-
corded. Most of the dead and dying birds were washed ashore by
storms, and nearly all the birds were severely emaciated. Although
OCR for page 170
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OCR for page 172
172
ARSENIC
TABLE 5-9 Results of Feeding Arsenic Trioxide-Poisoned Grass-
hoppers to Wild Birdsa
Species Arsenic Total Dose, mg Comment
Bobwhite quail 141 No effect observed
Mockingbird (nestling) 27.2 Matured
Robin (nestling) 40 Matured
Meadowlark (nestling) 17.2 Matured
Redwing blackbird (nestling) 13.8 Matured
Brown thrasher (nestling) 5.7 Died
Dickcissel (nestling) 10 Matured
Orchard oriole (nestling) 10.9 Matured
Scissortail (nestling) 12.2 Matured
English sparrow (nestling) 10 Matured
aDerived from Whitehead.854
extensive pathologic, microbiologic, and chemical testing was con-
ducted, no conclusive explanation for the deaths was determined. The
arsenic content of livers from 36 guillemots ranged from less than 0.1 to
41 ppm (dry basis), with an average of 7.1 ppm. Of the 36 samples, only
five contained arsenic at more than 10 ppm. Furthermore, apparently
healthy birds shot in the same area were found to contain arsenic at
0.7-20 ppm (average, 5.6 ppm) in their livers. These data are similar to
those obtained on the birds in the dieoff and do not indicate that arsenic
was directly involved in this instance.
Representative terms from entire chapter:
arsenic trioxide
