Chemical Form and Bioaccessibility of Mercury in Traditional Tibetan Medicines

Extremely high mercury (Hg) concentrations have been identified in traditional Tibetan medicine (TTM) products, but the chemical form and bioaccessibility of Hg remain unknown. We conducted experiments to explore whether the Hg contained in TTM is toxic. We determined that HgS is not the exclusive form of Hg in TTM; other compounds could be present in substantial quantities, ranging from 2 to 52% of the total Hg in commonly used TTMs. A substantial amount of Hg could be released from TTM after ingestion. In total, an average of 12 mu g of Hg (mostly inorganic)/g (range of 0.41-25 mu g of Hg/g) in TTMs was released into the liquid phase in simulated human gastro-intestinal environments. However, different from the results from ngestion by fish, the release of Hg from TTM in the intestinal environment is larger than that in the gastric environment by a factor of 2. In the case of joint ingestion with protein-rich products, releases of methyl Hg and inorganic Hg from TTM in gastrointestinal environments could be significantly enhanced by factors of 9 and 6, respectively. Our efforts further highlight that the Hg contained in TTMs could be harmful to human health, and the clinical safety of different TTM products should be thoroughly evaluated.