Illegal mining in Latin America

The water supply has also been affected. Thirty to forty tonnes of mercury are pumped into rivers in the region each year. Unsurprisingly, it has worked its way through the food chain. By analysing hair samples, another Carnegie study found that 78% of people in Madre de Dios had three times the usual concentration of mercury in their bodies. Some were more than 27 times over the international limit.
http://www.economist.com/blogs/americasview/2014/09/illegal-mining-latin-america