Methylmercury and inorganic mercury in Chinese commercial rice: Implications for overestimated human exposure and health risk

Xiaohang Xu,Jialiang Han,Jian Pang,Xun Wang,Yan Lin,Yajie Wang,Guangle Qiu

doi:10.1016/j.envpol.2019.113706

Abstract

China is the largest rice producer and consumer in the world, and mercury (Hg) levels, particularly methylmercury (MeHg), in rice and health exposure risks are public concerns. Total Hg (THg) and MeHg levels in 767 (domestic = 709 and abroad = 58) Chinese commercial rice were investigated to evaluate Hg pollution level, dietary exposures and risks of IHg and MeHg. The mean rice THg and MeHg levels were 3.97 ± 2.33 μg/kg and 1.37 ± 1.18 μg/kg, respectively. The highest daily intake of MeHg and IHg were obtained in younger groups, accounted for 6% of the reference dose-0.1 μg/kg bw/day for MeHg, 0.3% of the provisional tolerance week intake-0.571 μg/kg bw/day for IHg. Residents in Central China and Southern China meet the highest rice Hg exposure, which were more than 7 times of those in Northwest China. Lower concentrations than earlier studies were observed along the implementations of strict policies since 2007. This may indicate that a declining temporal trend of Hg in Chinese grown rice and associated exposures could be obtained with the implementations of strict policies. Though there exist Hg pollution in commercial rice, Hg levels in Chinese commercial rice is generally safe compared with Hg polluted sites. Populations dwelling in China have relatively a quite low and safe MeHg and IHg exposure via the intake of commercial rice. Strict policies contributed to the decrease in THg and MeHg levels in Chinese-grown rice. More attention should be paid to younger groups.

Highlights

Mercury (Hg) pollution in rice has become an emerging topic of concern since the beginning of this century
A few studies have reported the total Hg (THg) levels in rice from Chinese markets, demonstrating a range of
Residents in Central China and Southern China meet the highest rice Hg exposure, which were more than 7 times of those in Northwest China

Summary

Introduction

Mercury (Hg) pollution in rice has become an emerging topic of concern since the beginning of this century. In 2003, Horvat and colleagues firstly observed high MeHg levels in rice collected from the Wanshan mercury mine in southwestern China, the world’s third largest mercury mine (Horvat et al, 2003). Subsequent studies have found that rice consumption constitutes >94% of the MeHg exposure for residents in Guizhou province, southwestern China, who seldom eat fish (Zhang et al, 2010a). With the knowledge that rice intake is an important human MeHg exposure source in polluted areas (Feng et al, 2008), public concern has risen in recent years, mainly because rice is the staple food of more than half of the world’s population (FAOSTAT, 2019). A large number of scientists have started to study Hg biogeochemistry in rice plants and rice paddies (Krupp et al, 2009; Liu et al, 2019a; Rothenberg and Feng, 2012; Rothenberg et al, 2014; Strickman and Mitchell, 2017; Windham-Myers et al, 2014; Xu et al, 2016)

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