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7/14/2009 5:02:29 PM
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5/20/2009 10:14:01 AM
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UCREFRP
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
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CHEMICAL AND BIOCHEMICAL PROPERTIES <br />Elemental arsenic is a gray, crystalline material characterized by atonic <br />number 33, atomic webght of 74.92, density of 5.727, melting point of 817 C, <br />sublimation at 613 C, and chemical properties similar to those of phosphorus <br />(Woolson 1975; NAS 1977; NRCC 1978; EPA 1980; 1985). Arsenic has four valence <br />states: -3, 0, +3, and +5. Arsines and methylarsines, which are <br />characteristic of arsenic in t 9 e -3 oxidation state, are generally unstable in <br />air. Elemental ar?jnic, As , is formed by the reduction of arsenic oxides. <br />Arsenic trioxide (As ) is a product of smelting operations and is the <br />material used in synthesizing most arsgicals. It is oxidized catalytically <br />or by bacteria to arsenic pentoxide (As ) or orthoarsenic acid (H As04). <br />Arsenic in nature is rarely in its free state. Usually, it is a compo hnt of <br />sulfidic ores, occurring as arsenides and arsenates, along with arsenic <br />trioxide, which is a weathering product of arsenides. Most arsenicals degrade <br />or weather to form arsenate, although arsenite may form under anaerobic <br />conditions. Biotransformations may occur, resulting in volatile arsenicals <br />that normally are returned to the land where soil adsorption, plant uptake, <br />erosion, leaching, reduction to arsines, and other processes occur. This <br />natural arsenic cycle reflects a constant shifting of arsenic between <br />environmental compartments. <br />Arsenic species in flooded soils and water are subject to chemically and' <br />microbiologically mediated oxidation or reduction and methylation reactions. <br />At high Eh values (i.e., high oxidation-reduction ?gtential) typical of those <br />encountered in oxygenatSd waters, pentavalent As tends to exist as H Aso , <br />H Aso -, HAsO and AsO4 At lower Eh_, the corresponding trivalent arsenic <br />X cias can b present, as well as AsS (Thanabalasinm and Pickering 1986). <br />In aerobic soils, the dominant arseni? species was As , and small quantities <br />of arsenite and monom?jhylarsonic acid were present in mineralized areas; in <br />anaerobic soils, As was the major soluble species (Haswell et al. 1985). <br />Inorganic arsenic is more mobile than organic arsenic, and thus poses greater <br />problems by leaching into surface waters and groundwater (NRCC 1978). The <br />trivalent arsenic species are generally considered to be more toxic, more <br />soluble, and more mobile than As species (Thanabalasingam and Pickering <br />1986). Soil microorganisms metabolize arsenic into volatile arsine <br />derivatives. Depending on conditions, 17% to 60% of the total arsenic present <br />in soil may be volatilized (NRCC 1978). Estimates of the half-life of arsenic <br />7
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