The three 'B' of fish mercury in China: Bioaccumulation, biodynamics and biotransformation

Mercury (Hg) is a global toxic pollutant and has raised the world's attention for decades. In this study, we reviewed the fish mercury levels in China (both marine and freshwater, as well as wild and farmed) documented over the past decade and their controlling environmental and biological factors. China is the largest contributor of global Hg cycling and the largest nation for the consumption and export of fish and fish product, thus Hg level in fish becomes a critical issue for food safety and public health. In China, Hg in fish is generally accumulated at a low level, but significant geographical differences were evident and formed the "hot spots" from the north to the south. For marine fish, the east (median: 70 ng g^-1 ww, range: 5.0-330 ng g^-1 ww) and southeast (median: 72 ng g^-1 ww, range: 0.3-329 ng g^-1 ww) of China have higher total Hg concentrations than the other coastal areas. For freshwater fish, Tibetan Plateau exhibited the highest total Hg levels (median: 104 ng g^-1 ww, range: 5.0-868 ng g^-1 ww). Risk assessment of the exposure of low-Hg-level fish to China's population deserves more attention and detailed fish consumption advisories to specific populations are urgently needed. The biokinetic model is a useful tool to characterize the underlying processes involved in Hg accumulation by fish. The diet (Hg concentration, speciation, food quality and quantity) and growth appear to be the important factors affecting the Hg levels of fish in China. The Hg biotransformation can also make contributions to Hg speciation and overall accumulation in fish. The intestinal microbes play an important role in Hg biotransformation and the potential for minimizing Hg contamination in fish deserves further investigation.