Fate of arsenicals in different environmental substrates.

Abstract

The current knowledge of arsenic (As) transformations in the environment, as well as some gaps in this knowledge, are reviewed. These transformations involve As chemical and biochemical transformations in air, waters, sediments, and soils. Arsenic moves in a dispersive manner through air and water and is in physical and chemical equilibrium in many substrates. It is oxidized, reduced, methylated, volatilized, incorporated into biotic tissues, excreted, adsorbed, and desorbed. Oceanic sediments become the eventual sink for As. The rates of As movement and transformation vary with environmental conditions. Besides inorganic As, various methylated arsenicals are found naturally at environmentally sensitive equilibrium concentrations, which are probably maintained biotically. An As-transformation model has been constructed from rate constants derived from field observations. The environmental factors affecting these rate constants are discussed.

Potential impact of acid precipitation on arsenic and selenium.

“…In addition to physicochemical factors, a reasonably well established data base now exists to show that a number of biotransformations involving arsenicals occur in aquatic and terrestrial ecosystems (3)(4)(5). These bio- transformations are mediated by microbiota and higher level organisms, systems which are sensitive to media acidity.…”

“…The behavior of various arsenicals, particularly the inorganic and methylated forms, in soils is a function of soil type, metal colloid content, redox potential/acidity, relative phosphate content, the chemical form of arsenical, and microbiotic populations (36). The metalloid can be mobilized from and through soils by such factors as volatilization due to biotransformation, leaching downward, uptake by plant species, and runoff processes (36).…”

“…The metalloid can be mobilized from and through soils by such factors as volatilization due to biotransformation, leaching downward, uptake by plant species, and runoff processes (36).…”

“…The relative immobilization of inorganic arsenic and those organoarsenicals used as biocides in soil zones appears to be a function of metal (iron and aluminum) hydrous oxide content (36).…”

“…(4) Both As and Se enter complex geochemical and biogeochemical cycling/transformation processes, the relative expression of which determines overall environmental cycling and human exposure. (5) Environmental acidification has the potential for interacting with these processes in a multiplicity of ways. As with other environmental agents, there are some specific questions which help frame the issue of acid precipitation and its potential impact on the health aspects of As and Se.…”