To determine the amounts of arsenic compounds, such as arsenate, arsenite, monomethylarsonate (MMA), and dimethylarsinate (DMA) in soils, we developed an analytical technique that included solvent extraction, anion-exchange chromatography, and final determination of As by flameless atomic absorption spectrophotometry (FAA). This technique was successfully applied to typical As-polluted soils in Japan. As a result, arsenate was found to be the major component, and lower levels of DMA and MMA were also detected in most of the samples. (DMA: 4 to 69 ppb in paddy soils, 2 to 7 ppb in upland or orchard soils; MMA: 5 to 88 ppb in paddy soils, undetectable to 7 ppb in upland or orchard soils). In addition, two kinds of new As compounds (X1 and X2) were found and identified by field desorption-mass spectrometry. Seasonal variations of As compounds were also investigated in a rice field in Terayogai, Motoyoshi-town, Miyagi Prefecture. Consequently, the pH and the amounts of arsenite and DMA increased with the reduction of soil under flooded conditions, whereas the pH decreased and the amounts of arsenate and MMA increased under upland conditions.
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Takamatsu et al. (1982) studied this question.