| The minamata disease eruped in Minamata bay at 1950s', which was caused by the fish that with high mercury concentrations in it, made researchers start to pay more attention on mercury pollution in environment.The sources of mercury in environment contains both naturally source and artifical source, the latter one plays a big role in effecting the mercury in environment. Hgo is very stable when it is emissioned to the atmosphere, and it can stay in the air for a long while that it may take a part in the global mercury circulation. IHg can be methylated in certain condition after settling to the earth surface. Different from inorganic mercury, Methylmercury could be absorbed and Biomagnification in higher trophic levels in food chain. In the countries and regions which the residents eat more fish, such as Japan and some europe countries, fish is the most important medium for human mercury exposure. However, in China, especially inland parts, the intake of fish is much lower. Compared with other kinds of crops, the biological concentration factor of mercury in rice plant was much higher. The methylmercury concentration in rice plant was 10-40 times of the other crops. For the residents who take rice as their main food, the contribution of rice to human mercury exposure is very important.This research collected rice samples from 12 regions where produce rice plant in 2009, and these parts' rice production output took 81% of total production in China. Total mercury concentrations and methylmercury concentrations of rice samples were analysed. The daily input of total and methylmercury for both rural and urban residents were also estimated to assess human mercury exposure risk in the 12 parts. The contributions of different mercury exposure midium was calculated. Total mercury (THg) and methylmercury (MeHg) concentrations were measured with cold vapor atomic fluorescence spectrometry (CVAFS) after digesting and by alkaline-leaching and solvent extraction--aqueous-phase ethylation reaction, GC separation and CVAFS detection, respectively.The research results obtained after systemic analyzing are as followed:(1) The total mercury concentration of rice ranged from 0.78μg·kg-1 to 47μg·kg-1, the average concentration was 9.3±8.7μg·kg-1, and the median is 5.6μg·kg-1,64% of the samples'THg was lower than 7μg·kg-1.11% samples from Guangdong, Jiangxi, Hubei, Hunan, Guizhou and Jiangsu exceeded the maximum allowed level of THg (20μg·kg-1) in foods in China, this might because of the mercury emission of industry activity, fossil fuel burning, mining activity and the nonferrous metallurgy.(2) The mean methylmercury concentration was 2.3±2.3μg·kg-1, while the median was 1.8μg·kg-1, average MeHg concentrations from different parts varied from 0.29μg·kg-1 to 3.2μg·kg-1, and 80% samples' value were below 3.0μg·kg-1. Only 4 samples'MeHg concentrations from Hunan exceeded 10μg·kg-1, which were 11μg·kg-1,17μg·kg-1,18μg·kg-1,18μg·kg-1, respectively. The singular high levels of MeHg in these samples may be resulted of considerable MeHg in its paddy soil.(3) The daily intake of THg for urban and rural residents were 0.075～0.20μg/kg·bw,0.054～0.22μg/kg·bw, respectively. The maximum one was 0.36μg/kg·bw. Mediums(such as rice, vegetables, aquatic products)contributed the human mercury health risk together, the contributions were different from each other because of different dietary behavior and different THg concentration. The daily intake of MeHg for urban people are 0.0098～0.021μg/kg·bw on average, the maximum value was 0.76μg/kg·bw, for rural people, PDI of MeHg were 0.0070～0.025μg/kg·bw, but the maximum value of Hunan was 0.12μg/kg·bw, which had exposure risk of 120%. Research found that the sources of human MeHg exposure mostly were from rice and aquatic products, the sum of their methylmercury exposure contributions were above 94%.According to the results of this research, we come to the following important conclusions:(1) The rice didn't suffer from severe mercury pollution, the THg and MeHg concentrations both situated low levels in general; (2) The daily intake of THg and MeHg for urban and rural residents were much lower than PTWI of THg & MeHg recommended by WHO and FAO and RfD of MeHg suggested by USEPA, except that people in Hunan rural area had a risk of MeHg exposure; (3) The sources of human THg exposure mostly were from rice, vegetables and aquatic products, while MeHg health risk mediums were almost rice and aquatic products.
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