Adsorption and mobility of aromatic arsenicals in Japanese agricultural soils

We investigated the adsorption and mobility of aromatic arsenicals (AAs) in two types of Japanese agricultural soils in batch and column leaching experiments. The amounts of AAs adsorbed onto a Fluvisol (a sandy loam) and an Andosol (a light clay) decreased in the order of phenylarsonic acid (PAA) > methylphenylarsinic acid (MPAA) > diphenylarsinic acid (DPAA) > methyldiphenylarsine oxide (MDPAO) > dimethylphenylarsine oxide (DMPAO). The amounts of all AAs adsorbed onto the Andosol, which had more amorphous minerals and organic carbon, were higher than those adsorbed onto the Fluvisol. The adsorbability of AAs increased with both an increasing arsenate proportion and a decreasing hydrophobicity. This result suggests that the mechanisms of adsorption of AAs onto soil are due mainly to ligand exchange reactions and less to hydrophobic interactions. Mobility in the Fluvisol decreased in the order of DMPAO (30 cm) > MDPAO (25 cm) > MPAA (20 cm) > DPAA (15 cm) = PAA (15 cm). Mobility in the Andosol was less: DMPAO (15 cm) = MDPAO (15 crn) > DPAA (10 cm) > MPAA (5 cm) = PAA (5 cm). The mobility of MDPAO and DMPAO was higher than that of PAA and MPAA, and all AAs were less mobile in the Andosol than in the Fluvisol.