Arsenic Speciation in Rice Paddy Soils.

Arsenic can undergo several chemical and microbial transformations in soil, including oxidation/reduction, methylation/demethylation, and volatilization, which could impact arsenic bioavailability for plant uptake. An experiment was conducted in field plots at Stuttgart, AR to determine whether arsenic concentration and water management (flooded versus saturated) impact the speciation and transformation of soil arsenic. The treatments were: (1) fallow and planted with the rice variety “Wells”; (2) saturated and flooded, and (3) a moderate arsenic concentration native soil and an adjacent soil amended with monosodium methanearsonate (MSMA). Soil samples were collected prior to planting, after flooding, and prior to harvest and analyzed for total arsenic and arsenic speciation.  Arsenic species were determined by HPLC-ICP-MS following extraction. These results will help to determine if different water management systems can alter arsenic speciation in soil and ultimately affect plant uptake of arsenic.