Methylmercury in rice (Oryza sativa L.) grown from the Xunyang Hg mining area, Shaanxi province, northwestern China

Abstract

Mercury (Hg) is a global pollutant and can transform into methylmercury (MeHg), a highly toxic and bioaccumulative organic form. Recent surveys showed that rice (Oryza sativa L.) rather than fish is the main source of human MeHg exposure in Hg mining and retorting regions in Guizhou province, southwestern China, where rice is a traditional staple food. Here we report that MeHg in rice grown at an active Hg mining and retorting region in Shaanxi province, northwestern China, characterized with different climate compared to Guizhou, contained levels up to 240 μg kg–1 MeHg in bran, 78 μg kg–1 MeHg in polished rice, and 30 μg kg–1 MeHg in hull, respectively. Although the polishing process may reduce MeHg content, the mass balance calculation showed that greater than 50 % of total MeHg mass can be observed in white rice (polished rice). The ongoing Hg retorting activities, which account for the high levels of ambient air Hg, result in high levels of MeHg in rice grains. Our results further demonstrate that the accumulation of MeHg is a common feature of rice.