Methylmercury in Chinese-grown and imported rice on sale in China: implications for human exposure health risk

Xiaohang Xua,b, Jialiang Hana, Runsheng Yinc, Jian Pand, Xun Wanga, Yan Line, Yajie Wangf and Guangle Qiua*

aState Key Laboratory of Environmental Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, China

bUniversity of Chinese Academy of Sciences, China

cState Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, China

dGuizhou Normal University, China

eNorwegian Institute for Water Research, Norway

fCollege of Food Safety, Guizhou Medical University, China

xuxiaohang@vip.skleg.cn

In recent years, rice was found to have the methylmercury (MeHg), and rice consumption was identified to be the major pathyway of MeHg exposure in mercury (Hg) mining areas in China. As China is the largest rice producer and consumer in the world, rice Hg and its associated exposure risk has been of public concerns. Our objectives were to thoroughly investigate total Hg (THg) and MeHg levels in rice sold in Chinese market, and evaluate the exposures and risks of inorganic Hg (IHg) and MeHg via rice intake for Chinese residents. The temporal trend of Hg levels in Chinese producing rice and the Hg exposure were also investigated. Rice samples of 767 brands were collected from Chinese markets according to the producing areas. Results of THg and MeHg in commercial rice were measured. Sensitivity and uncertainty was performed by Monte-Carlo simulation. The exposures and risks of IHg and MeHg for different age-gender groups were calculated under the conditions of without and with consideration of bioaccessibilities of THg and MeHg. The body weights and rice intake rates of different age-gender groups are according to the Chinese National Nutrition and Health Survey. The average rice THg and MeHg levels were 3.97±2.33 µg/kg and 1.37±1.18 µg/kg, respectively. The highest daily intake were obtained in younger groups (2-4 years old for female and 4-7 years old for female), accounting for 6% of the reference dose (RfD)-0.1 µg/kg bw/day for MeHg, 0.3% of the provisional tolerance week intake (PTWI)-0.571 µg/kg bw/day for IHg. When considering the bioaccessibilities of THg and MeHg, the values were much lower than those without considering bioaccessibilities. Relatively lower concentrations than earlier studies were found since 2007. This may suggest a declining temporal trend of THg and MeHg in Chinese producing rice and associated Hg exposures. Generally, Chinese residents met a low and safe MeHg and IHg exposure via rice consumption. Effective Hg pollution control measures taken lead to the decline of THg and MeHg levels in Chinese grown rice. In future, more focus should be paid to effect of chronic Hg exposure of younger groups, especially those in Hg polluted sites.

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