Would you like some mercury with that fish?
Several small studies have shown that some fish in the Madre de Dios region in southeastern Peru contain dangerous levels of mercury. A larger study of mercury in fish and in people will soon get under way under the direction of Luis Fernández, a tropical ecologist from the Carnegie Institution for Science at Stanford University.
“We’re going to focus on measuring the amount of mercury in consumable fish in the rivers and lakes of Madre de Dios and the concentration ofmethylmercury in the hair of members of rural and urban communities in various watersheds in Madre de Dios,” Fernández told me.
Madre de Dios is the epicenter of a gold rush that is accelerating deforestation and polluting watersheds. Miners use huge sluices to collect sand laced with flecks of gold, and then add mercury to amalgamate the gold and separate it from the sediment. The result is a lump called a “sponge,” which is heated — often over an open flame — to vaporize the mercury, leaving behind a nugget of gold.
Miners sell those nuggets at gold shops, where they are heated again to drive off any remaining mercury. Those shops are often on busy streets in larger towns, where passers-by are exposed to mercury vapor.
While the environmental impacts of mining in Madre de Dios get a lot of attention, little is said about the health impacts of mercury exposure. Elemental mercury — the kind inhaled as vapor — can cause tremors, memory loss, muscle weakness, irritability, insomnia, headaches and reduced mental abilities. Last year, Fernández and a team of researchers from the US Environmental Protection Agency found alarming levels of mercury in the air in and around shops where gold is bought and sold inPuerto Maldonado, the capital of Madre de Dios.
Some mercury is dumped — or precipitates — into streams, where bacteria convert it into methylmercury. That form of mercury accumulates in the tissues of fish, becoming more concentrated higher up the food chain. Levels are highest in fish that eat other fish, as well as in creatures at the top of the food chain, including river otters, harpy eagles and humans.
If a woman who is pregnant eats fish containing high levels of methylmercury, that mercury can cross the placenta and affect the development of her unborn child. Methylmercury can also cross the barrier that normally protects the brain from toxics, so anyone can be at risk.
“We’re expecting to find that fish that live in watersheds downstream from areas where there is artisanal gold mining will have higher levels of mercury than those in pristine areas,” Fernández said. “We’re expecting that people who routinely consume fish in areas downstream from mining areas will be at greater risk for methylmercury poisoning.”
Two years ago, Fernández and colleagues found high levels of methylmercury in several fish species commonly sold in local markets. Those results and the air-quality study paved the way for this broader 18-month study, which will be funded by the Blue Moon Foundation. Fernández expects to have preliminary results by the end of the year.
For more about the gold rush in Madre de Dios, see my articles:
This paper by researchers from Duke University, the Ecole Nationale des Ingénieurs des Travaux Agricoles de Bordeaux, and CESEL S.A. in Lima:
And this collection of articles from the Peruvian Environmental Law Society (Sociedad Peruana de Derecho Ambiental, SPDA)