7092

• UCREFRP Catalog Number: 7092
• Author: Eisler, R.
• Title: Arsenic Hazards to Fish, Wildlife, and Invertebrates
• USFW Year: 1988.
• USFW - Doc Type: A Synoptic Review.
• Copyright Material: NO

dimethylarsine, and may volatilize to the atmosphere where oxidation reactions
result in the formation of dimethylarsinic acid (Woolson 1975). Arsenates are
more strongly adsorbed to sediments than are other arsenic forms, the
adsorption processes depending strongly on arsenic concentration, sediment
characteristics, pH, and ionic concentration of other compounds (EPA 1980). An
important mechanism of arsenic adsorption onto lake sediments involves the
interaction of anionic arsenates and hydrous iron oxides. Current evidence
suggests that arsenic is incorporated into sediments at the time of hydrous
oxide formation, rather than by adsorption onto existing surfaces (Aggett and
Roberts 1986). Arsenic concentrations in lake sediments are also correlated
with manganese; h&ous manganese oxides--positively charged for the
adsorption of Mn ions--play a significant role in arsenic adsorption onto
the surface of lake sediments (Takamatsu et al. 1985). The mobility of
arsenic in lake sediments and its release to the overlying water is related
partly to seasonal changes. In areas that become stratified in summer,
arsenic released from sediments accumulates in the hypolimnion until turnover,
when it is mixed with epilimnetic waters; this mixing may result in a 10 to
20% increase in arsenic concentration (Aggett and O'Brien 1985).
MicroorganisTj (inclgding four species of fungi ?5in lake Wiments oxidized
inorganic As to As and reduced inorganic As to As under aerobic
conditions; under anaerobic conditions, only reduction was observed (Freeman
et al. 1986). Inorganic arsenic can be converted to organic alkyl arsenic
acids and methylated arsines under anaerobic conditions by fungi, yeasts, and
bacteria--although biomethylation may also occur under aerobic conditions (EPA
1980).
Most arsenic investigators now agree on the following points: (1)
arsenic may be absorbed by ingestion, inhalation, or through permeation of the
skin or mucous membranes; (2) cells accumulate arsenic by using an active
transport system normally used in phosphate transport; (3) arsenicals are
readily absorbed after ingestion, most being rapidly excreted in the urine
during the first few days, or at most a week (the effects seen after long-term
exposure are probably a result of continuous daily exposure, rather than of
accumulation); (4) the toxicity of arsenicals conforms to the following order,
from greatest to least toxicity: arsines > inorganic arsenites > organic
trivalent compounds (arsenoxides) > inorganic arsenates > organic pentavalent
compounds > arsonium compounds > elemental arsenic; (5) solubility in water
and body fluids appears to be directly related to toxicity (the low toxicity
of elemental arsenic is attributed to its virtual insolubility in water and
body fluids, whereas the highly toxac arsenic trioxige, for example, is
Soluble in water to 12.0 g/1 at 0 C, 21.0 g/1 at 25 C, and 56.0 g/1 at 75
C); and (6) the mechanisms of arsenical toxicity differ considerably among
arsenic species, although signs of poisoning appear similar for all arsenicals
(Woolson 1975; NRCC 1978; Pershagen and Vahter 1979).
The primary toxicity mode of inorganic As +3 is through reaction with
sulfhydryl groups of proteins and subsequent enzyTj inhibition; inorganic
pentavalent arsenate does not react as readily as As with sulfhydryl groups,
9