US EPA

1378682 

Technical Report 

Fate of organic arsenicals in soils and plants 

Ray, B 

1975 

PESTAB/75/2089 

Pest 

1 

9-14; 1975 

PESTAB. The use of 2 organic arsenicals, monosodium acid methanearsonate (MSMA) and disodium methanearsonate (DMSA), as herbicides in cotton crops is discussed with respect to their fate in the soil and their metabolism and toxicity in plants. In the soil, MSMA is oxidized by microorganisms to inorganic orthoarsenic acid and carbon dioxide or is reduced and methylated by microorganisms to volatile methylarsines, primarily dimethyl arsine. Some of the ortho-arsenic acid is converted to insoluble salts of iron, aluminum, and calcium, and some is converted to volatile methylarsines. The latter are produced in very low concentrations and are transported by air to other areas. They are eventually oxidized in air and the arsenical oxidation products are redeposited in other soils by the actions of gravity and rainfall. The ultimate result of this microbiological, metabolism is a redistribution of soil arsenic from areas of high available arsenic to areas of low available arsenic. The amount of available arsenic in a soil is influenced by such factors as soil surface area, organic matter content, ion exchange sites, and the availability of ions such as iron, aluminum, and calcium, which can form water-insoluble arsenical salts.