A new study out of China shows that for millions of people at risk of eating toxic amounts of mercury-laced food, fish isn’t the problem. Rice is.
Mercury, once released into the environment can be methylated by bacteria to produce methylmercury, a potent neurotoxicant. Methylmercury poisoning has been linked with diminishing the IQ of children exposed in the womb and with raising blood pressure and other heart-disease risks among adults. Methylmercury is bioaccumulated especially in the marine food-chain. Because of the high concentrations resulting from the bioaccumulation, fish consumption is considered the primary pathway of methylmercury (MeHg) exposure for most people in the world. However, in the inland regions of China, most of the residents eat little fish, but they live in areas where a significant amount of mercury (Hg) is present in the environment.The new study:
To investigate salient MeHg exposure for the general adult population in Inland China, Zhang and his colleagues selected four locations within Guizhou Province representing typical rural areas, where the diet is primarily locally grown agricultural products: Wanshan (Hg mining and smelting activities), Qingzhen (coal-fired power plant), Weining (artisanal zinc smelting activities), and Leigong Natural Reserve (no direct Hg contamination sources).
Methylmercury and total mercury exposure through drinking water, diet, and respiration were assessed for adults in the four regions by performing mercury speciation analsis. Previous sampling provided data for air, water, fish, meat, and poultry, while agricultural products (rice, corn, and vegetables), drinking water from Wanshan and Leigong, and total gaseous mercury in Wanshan were newly evaluated in this study. These data were collectively used to calculate probable daily intakes for the general adult population.
Although mercury exposures for these communities varied dramatically, in every one of them “rice accounted for 94 to 96 percent of the probable daily intake of methylmercury”. Guizhou’s heavy cereal contamination traces in large part, the study says, to the fact that rice paddies harbor the types of bacteria that can convert inorganic mercury to its more toxic, methylated form. The probable daily intake (PDI) of MeHg was considerably higher in people living in Wanshan than in the other areas; approximately 34% of Wanshan residents exceeded the reference dose for MeHg established by the U.S. Environmental Protection Agency. The MeHg PDI in the other three locations were all below the reference dose. The new study
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last time modified: September 15, 2010