Uptake of Organic Arsenic Species By Rice.

Rice (Oryza sativa) is a staple food crop in many regions of the world and its contamination by arsenic constitutes a substantial health risk to many consumers. Recent research has begun to identify pathways that may ultimately be used to decrease the health risk posed by contaminated rice. Under reduced conditions, arsenite can enter rice roots through a silicic acid transporter, which has prompted competition studies at field scales. However, less is known about how organic forms of arsenic enter rice. Dimethyl arsenic acid (DMA) and monomethyl arsenic acid (MMA) have been found in rice grains, particularly in rice grown in the southern United States. Researchers have suggested that DMA and MMA also enter the rice root via silicic acid transporters. To test the ability of silicic acid to compete with MMA and DMA at relevant concentrations, we performed hydroponic experiments with varying levels of silicic acid additions. Rice biomass and arsenic concentrations were measured at the completion of vegetative and reproductive stages. Preliminary data indicate that MMA decreased rice biomass, while silicon additions had negligible effect on biomass. Data will also be presented from a field-scale experiment where several agronomically relevant silicon amendments were added to rice paddies. Collectively, this research provides insights into whether silicon amendments can decrease rice uptake of organic arsenic species.