Occurrence of Per- and polyfluoroalkyl substances in Wheat, Maize, Rice, and Soybean from Chinese Major Grain Producing Regions

Dietary exposure to per- and polyfluoroalkyl substances (PFAS) has been a concern for many years. Previous studies demonstrated that foods such as meat, milk, fish, vegetables, and tuber crops could be potential sources of human exposure to PFAS. However, research on PFAS contamination in grains remains limited. Therefore, this study conducted a comprehensive investigation of PFAS contamination in raw grains from major grain-producing regions in China. Among all grain species, soybeans exhibited the highest Σ₁₆PFAS level (1.01 ng/g dw), followed by rice (0.570 ng/g dw), wheat (0.542 ng/g dw), and maize (0.245 ng/g dw). Short-chain perfluoroalkyl carboxylates (PFCAs) displayed higher detection frequencies compared to their long-chain homologues and perfluoroalkyl sulfonates (PFSAs). Perfluorobutanoic acid (PFBA) and perfluorooctanoic acid (PFOA) were dominant in wheat, maize, and soybean samples, while sodium p-perfluorous nonenoxybenzenesulfonate (OBS) was predominant in rice. OBS contributed approximately 70% to Σ₁₆PFAS concentrations in rice. The concentration difference of OBS was not significant between indica rice and japonica rice, however, a disparity was observed between early indica rice and mid-late indica rice, suggesting that the growing period potentially affects OBS level in rice grains. Compared to other regions, east China displayed relatively higher PFAS concentrations in grain samples. This finding is consistent with previous studies and may be attributed to the intensive industrial and human activities. The estimated daily intake (EDI) of Σ₁₆PFAS in grains from this study ranged from 0.0829 to 3.32 ng/kg bw/day. The dietary health risks associated with PFOA in wheat and OBS in rice warrant further attention.