Total grain-arsenic and arsenic-species concentrations in diverse rice cultivars under flooded conditions

Arsenic (As) is not an essential element and can be toxic to both plants and animals. Low As concentrations in all foodstuffs, including rice grain, is a desirable goal because of the potential detrimental impacts of As on plant growth and yield and its potential toxicity to humans. Twenty-five diverse rice (Oryza sativa L.) cultivars, including both indica and japonica subspecies, were grown over a 3-yr period (2004, 2005, and 2007) on a moderate As-concentration, paddy soil (Dewitt silt loam, fine, smectitic, thermic Typic Albaqualf) under continuously flooded field conditions. The total grain-As [TGAs; HNO₃/H₂O₂ digestion and analysis by inductively-coupledplasma mass-spectroscopy (ICP-MS)] and Asspecies [trifluoroacetic acid (TFA) extraction and analysis by high performance liquid chromatography (HPLC) coupled with ICP-MS] concentrations and their relationships with plant-growth parameters (e.g., heading date and yield) were assessed. The only As species detected in milled (polished) rice grain were inorganic As^III (arsenite) (iAs^III) and dimethylarsinic acid (with pentavalent As) (DMAs^V). Total grain-As (TGAs) and As-species concentrations, as well as iAsIII/ TGAs ratio, each varied widely between cultivars. Arsenic concentration and speciation were mostly dependent on genotype (G), but there were also significant genotype by year (G × Y) and year (Y) effects that were likely impacted by annual differences in environmental conditions, such as temperature, and local soil characteristics. This study indicates the significant potential for lowering rice-grain As concentration through genotype selection and plant breeding.