By comparing the mercury isotopic composition in human hair and dietary sources for Chinese inland population, the major mercury exposure sources were identified.
Background:Mercury is a global pollutant. Following emission mainly from combustion sources, inorganic mercury is readily transformed to methylmercury, a toxin causing neurological damages. Methylation of Hg occurs microbially in aquatic ecosystems, and bioaccumulation of MeHg along the food chain can result in high levels of MeHg in fish and other organisms at the top of the food chain. Therefore, fish consumption is considered the major exposure route of Hg to humans. Dietary mercury exposure due to terrestrial sources is generally lower, due to shorter food chain length. Unfortunately, heavy mercury pollution can also lead to contaminated crops. Rice paddies have been shown to enhance Hg methylation, explaining high MeHg levels in rice. For health risk assessment of populations living in such contaminated areas, the identification Hg exposure pathways is a prerequisite. Unfortunately, such evaluation is not straightforward, since numerous dietary and other sources must be investigated for their Hg levels and speciation.
Mercury stable isotope geochemistry has been demonstrated to provide useful information to trace Hg sources and biogeochemical processes of Hg in the environment. The seven stable isotopes of mercury can undergo fractionation, depending either on mass or magnetic isotope effects or nuclear volume. Combining the mass-depending fractionation (MDF) and the mass-independing fractionation (MIF) of Hg isotopes can provide information about sources and pathways of Hg in the environment. While no significant MDF and MIF of Hg isotopes has been observed during bioaccumulation of dietary MeHg in fish, an offset ~2‰ in δ202 Hg was observed between fish and tissues of fish-consumers, indicating that MDF of Hg isotopes occurs during metabolic processes in mammals.
The new study:
The international research group hypothesized that populations from Guizhou Province, China may have distinct hair isotopic signatures compared to previous results, since rice consumption is the most important pathway for human Hg exposure in Guizhou. To test this hypothesis, the group investigated the isotopic composition of Hg in hair samples of residents from three different areas in Guizhou Province (South China) representing a mining, an urban and rural area. Also, potential dietary sources, such as fish, rice and vegetables were studied as well.
Rice and vegetables showed low δ202 Hg and small negative to zero Δ199 Hg, while fish showed relatively higher δ202Hg and positive Δ199 Hg. Also, human hair samples from the different areas showed distinct isotopic signatures. Hair samples from residents of a mining area and a rural area displayed near zero Δ199 Hg, pointing to rice as the major exposure source. The hair from residents of the urban area showed positive Δ199 Hg likely caused by consumption of fish. A binary mixing model based on Δ199 Hg showed that rice and fish consumption accounted for 59% and 41% of dietary Hg sources for residents of the urban area, respectively, whereas rice is the major source for residents of the mining and rural area. These results were cross-checked by calculations of probable daily intakes, suggesting that the Hg isotope approach can be used to quantify exposure sources.
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Related EVISA Resources
Link Database: Mercury exposure through the diet Link Database: Environmental cycling of methylmercury Link Database: Environmental cycling of inorganic mercury Link Database: Environmental pollution of methylmercury Link Database: Environmental pollution of inorganic mercury Link Database: Toxicity of mercury
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