Rice Arsenic Accumulation Mitigated by Agricultural Sulfur Applications: Insights from Two-Year Mesocosm Experiments and a Meta-Analysis

Arsenic (As) accumulation in rice presents a global health concern, yet the impacts of expanding agricultural sulfur (S) applications on As behavior in rice systems remain inadequately understood. This study integrates two-year open-air mesocosm experiments with global meta-analysis to assess S effects on soil-to-grain As transfer. Mesocosm trials showed that sulfate fertilizers significantly reduced carcinogenic inorganic As (iAs) concentrations in white rice by up to 46% compared to nonsulfur controls, across different soils, irrigation regimes, and seeding practices. Meta-analysis further revealed consistent decreases in total As in grain (37%), leaves (25%), and stems (24%), but not in roots or iron plaque. Sulfur primarily suppressed root-to-grain iAs translocation rather than enhancing direct iron-plaque binding, as indicated by unchanged plaque As/Fe and positive correlations of grain iAs with root and stem As rather than with plaque As. However, sulfate addition increased porewater methylated As and tended to elevate grain dimethylarsenate, a precursor of highly cytotoxic dimethylated monothioarsenate (DMMTA), though grain DMMTA remained unchanged. Mitigation efficacy was more strongly influenced by soil pH and organic carbon than by total soil As. These findings support the targeted use of S fertilization to lower dietary iAs exposure, while emphasizing the importance of speciation-resolved monitoring to minimize unintended toxicological risks.