Bioaccessibility-corrected risk assessment of urban dietary methylmercury exposure via fish and rice consumption in China.

The role of seafood consumption for dietary methylmercury (MeHg) exposure is well established. Recent studies also reveal that rice consumption can be an important pathway for dietary MeHg exposure in some Hg-contaminated areas. However, little is known about the relative importance of rice versus finfish in MeHg exposure for urban residents in uncontaminated areas. Especially, the lack of data on MeHg bioaccessibility in rice hinders accurately assessing MeHg exposure via rice consumption, and its importance compared to fish. By correcting commonly used risk models with quantified MeHg bioaccessibility, we provide the first bioaccessibility-corrected comparison on MeHg risk in rice and fish for consumers in non-contaminated urban areas of China, on both city- and province-scales. Market-available fish and rice samples were cooked and quantified for MeHg bioaccessibility. Methylmercury bioaccessibility in rice (40.5±9.4%) was significantly (p<0.05) lower than in fish (61.4±14.2%). This difference does not result from selenium content but may result from differences in protein or fiber content. Bioaccessibility-corrected hazard quotients (HQs) were calculated to evaluate consumption hazard of MeHg for consumers in Nanjing city, and Monte Carlo Simulations were employed to evaluate uncertainty and variability. Results indicate that MeHg HQs were 0.14 (P50) and 0.54 (P90). Rice consumption comprised 27.2% of the overall dietary exposure to MeHg in Nanjing, while fish comprised 72.8%. Employing our bioaccessibility data combined with literature parameters, calculated relative contribution to MeHg exposure from rice (versus fish) was high in western provinces of China, including Sichuan (95.6%) and Guizhou (81.5%), and low to moderate in eastern and southern provinces (Guangdong: 6.6%, Jiangsu: 17.7%, Shanghai: 15.1%, Guangxi: 20.6%, Jiangxi: 22.8% and Hunan: 25.9%). This bioaccessibility-corrected comparison of rice versus fish indicates that rice consumption can substantively contribute to dietary MeHg exposure risk for urban populations in Asia, and should be regularly included in dietary MeHg exposure assessment.