Linear-no-threshold concept for evaluating arsenic toxicity in rice grains

Arsenic (As) is a potent carcinogen that enters the human food chain mainly through rice, which is one of the staple food crops worldwide. During February 2022, a market survey was conducted and 500 samples of rice grains were collected across 41 different locations in Mumbai/Navi-Mumbai. On the basis of grain As-accumulation, samples were grouped into three categories including low- (0-30 ng g^-1 DW), medium- (31-70 ng g^-1 DW) or high- (>71 ng g^-1 DW). The health risk assessment revealed that a significant proportion of samples under the mid-As category with As-level below WHO permissible limit of 100 ng g^-1 DW, have hazard quotient > 1, indicating significant risk considering the dietary intake of 400 g rice/day. Further, a combination of parboiling and absorption-based traditional Indian cooking method was found effective in significantly reducing As-accumulation by ∼0.4-fold, in lieu of marginal dietary supplement of essential nutrients like iron and manganese. The extracts of Kolam rice significantly increased the levels of reactive-oxygen species (ROS) and reduced glutathione (GSH) in murine lymphocytes, compared those grown on As-free soil, indicating redox imbalance. Taken together, the findings supported that "linear-no-threshold" concept should be followed for evaluating toxicity of As-contaminated rice grains, to be safe or unsafe for human consumption.