Traditional Tibetan medicine exposes people and environment to high mercury levels

Many people view the Tibetan Plateau, or "Roof of the World," as a pristine alpine environment, largely untouched by pollution. But researchers, reporting in ACS' journal Environmental Science & Technology, have now shown that traditional Tibetan medicine (TTM) exposes people and the environment to high levels of mercury and methylmercury.

Used by Tibetans for more than 1,000 years, TTM is a complex concoction of herbs and minerals in pill form. Pharmacists often add minerals to TTM that might contain mercury and other heavy metals in the belief that they have therapeutic effects. High levels of total mercury have been reported in TTM, but until now nobody has analyzed the amount of methylmercury—one of the most toxic forms of the element. Xuejun Wang and coworkers wanted to understand the life cycle of mercury and methylmercury from their ingestion in TTM to their release into the environment.

The researchers began by measuring total mercury and methylmercury concentrations in seven commonly used types of TTM. With this information, they estimated that the average probable daily intake of total mercury by Tibetans was 34-fold higher than in a region of China specializing in mercury mining and 200¬-3,000-fold higher than in Japan, Norway and the U.S. Probable intake of methylmercury was also higher in Tibet than in the other regions, except for in Japan, where high amounts of marine fish (another source of methylmercury) are consumed. In 2015, Tibetans excreted about 1,900 pounds of total mercury, mostly from TTM, into municipal sewage treatment plants and released about 7,900 pounds directly into the environment, the researchers estimated. Only about 3.2 ounces of methylmercury likely entered municipal sewage. However, actual methylmercury levels could be much higher because bacteria in sewage might convert inorganic mercury into the more toxic form, the researchers say.