Mercury Isotope Signatures of Methylmercury in Rice Samples from the Wanshan Mercury Mining Area, China: Environmental Implications

Rice consumption is the primary pathway of methylmercury (MeHg) exposure for residents in mercury-mining areas of Guizhou Province, China. In this study, compound-specific stable isotope analysis (CSIA) of MeHg was performed on rice samples collected in the Wanshan mercury mining area. An enrichment of 2.25in total Hg (THg) delta Hg-202 was observed between rice and human hair, and THg Delta Hg-199 in hair was 0.12higher than the value in rice. Rice and human hair samples in this study show distinct Hg isotope signatures compared to those of fish and human hair of fish consumers collected in China and other areas. Distinct Hg isotope signatures were observed between IHg and MeHg in rice samples (in mean +/- standard deviation: delta Hg-202(IHg) at -2.30 +/- 0.49, Delta Hg-199(IHg) at -0.08 +/- 0.04, n = 7; delta Hg-202(MeHg) at -0.80 +/- 0.25, Delta Hg-199(MeHg) at 0.08 +/- 0.04, n = 7). Using a binary mixing model, it is estimated that the atmospheric Hg contributed 31% +/- 16% of IHg and 17% +/- 11% of THg in the rice samples and the IHg in soil caused by past mining activities contributed to the remaining Hg. This study demonstrated that Hg stable isotopes are good tracers of human MeHg exposure to fish and rice consumption, and the isotope data can be used for identifying the sources of IHg and MeHg in rice