Genetic, Chemical, and Field Management Strategies for Reducing Accumulation of Arsenic in Rice Grains.

There is public concern over amounts of arsenic contained in rice grains and foods. The World Health Organization (WHO) has set a CODEX limit of 0.2 ppm inorganic arsenic (iAs) in milled white rice, and a lower limit of 0.1 ppm for baby food products. Arsenic is of greater concern in rice than other grain crops because the redox conditions in flooded rice paddies makes soil As more available for plant uptake. One method proposed for reducing grain-As concentrations is to produce rice without a flood for all or part of its production period, but this can increase pests and decrease yields. Because roots uptake As through phosphorus and silica transporters, application of P and Si fertilizers have also been evaluated. Our research has focused on identifying rice genes and physiological factors that can be exploited to reduce grain-As. From among 1763 widely diverse rice accessions, subsets of low grain-As and high grain-As accessions were selected and compared for As concentration and metabolism in leaves and roots under field and hydroponic conditions. Data indicated that reduced grain-As concentrations were not due to reduced root uptake or root-to-shoot transfer rates, but were associated with more efficient sequestration of As in leaf vacuoles, a process that involves several sulfur-containing compounds. The effects of foliar application of sulfur fertilizer were investigated, but were not found to reduce grain-As concentrations nor severity of As-toxicity symptoms.