Questions concerning environmental mobility of arsenic: needs for a chemical data base and means for speciation of trace organoarsenicals.

Abstract

Biomethylation of metals, including arsenic, apparently occurs as a global process. Health control strategies therefore depend on accurate analysis of arsenic's environmental mobility. Determining to what extent biotransformations occur and how resultant organometal(loids) are sequestered in food chains requires sophistication beyond present-day total element determinations. Rather, active molecular forms of arsenic must be speciated for each environmental compartment, and it is necessary to quantify the dynamics of arsenic's mobility. Thus, new chemical facts are needed yielding rates of methylation or demethylation of arsenic; partition coefficients of organoarsenicals between air, water, and organic phases; and arsenic redox chemistry in polar media. NBS research in this context is reviewed with examples of recent results emphasizing speciation methodology. Topic areas discussed are: the nature of aquated methylarsenic species (NMR and laser-Raman spectroscopy); transport of methylarsenicals from aqueous media (gas chromatography-graphite furnace AA detection applied to metabolic Me3As formation); and speciation of involatile organoarsenicals in aqueous media (demonstration of HPLC utilizing element-specific AA detection and appraisal of electrochemical detectors). IntroductionBiotransformations of metalloids such as arsenic have been known for years, but only in recent times has the ubiquitous biomethylation of arsenic (1) and a number of other elements, including heavy metals (2-4), become apparent as a general environmental process (5). Clearly, anthropogenic inputs in inorganic materials can and do enhance such transformations, resulting in transport of volatile or lipidsoluble pollutants. Moreover, there is evidence (6) that even higher organisms, specifically man, can invoke elimination processes which involve formation of methylarsenic compounds. Consequently,

Sources, Transport and Alterations of Metal Compounds: An Overview. I. Arsenic, Beryllium, Cadmium, Chromium, and Nickel

“…It has been suggested that increased utilization 55 of compounds containing cadmium has accelerated the rates of mobilization and transport of Cd which far exceed the rates of the natural, abiotic cycling processes (114). These rates have led to increased deposition of cadmium in atmospheric, aquatic and terrestrial environments with subsequent increased uptake of Cd by accumulation in the biota (114).…”

“…It is generally acknowledged that it is difficult to quantitate the degree of transport of arsenic due to complex multimedia (e.g., sediment/soil-water-biotaair) exchange of arsenic and the natural differences between air, soil, and water systems (55,57). Cycling of arsenic in the environment is dominated by adsorption and desorption to soils and sediments, and is maintained at low concentrations in water and air (57).…”

“…Cycling of arsenic in the environment is dominated by adsorption and desorption to soils and sediments, and is maintained at low concentrations in water and air (57). Alkyl arsines are formed in soils and possibly sediments and in sewage sludge (55,57,80), hence, transport can occur in air and water. While the transport of alkyl arsines in air may involve only the gaseous phase or a gaseous/particulate phase, the extent of transport in air is unknown (57).…”