Metabolic Fate of the Arsenical Fungicide, Ferric Methanearsonate, in Soil

Abstract

The metabolic fate of the fungicide MAF [ferric methanearsonate; (CH₃AsO₃)₃Fe₂] was studied in 3 cultivated soils under laboratory conditions. In the flooded soils, the monomethyl arsenic moiety of MAF disappeared with half-lives of 11-28 days. The primary product was an inorganic-arsenic (Inorg-As). Dimethyl-arsenic (DM-As) and trimethyl-arsenic (TM-As) compounds were also detected. The fates of sodium arsenate, dimethylarsinic acid and trimethylarsine oxide corresponding to the MAF metabolites were examined. The results indicate that ultimate fate of MAF is transformation to Inorg-As species. The fate of MAF was examined in the soils under 4 different conditions. Evolution of gaseous arsines was observed only in the soil amended with glucose under flooded conditions, and the TM-As was the principal component. The fate of MAF was compared with that of disodium methanearsonate (DSMA) under the similar 4 conditions of soils. The results indicate that MAF is much more persistent than DSMA, especially in moist soil.