Wildcat gold mining releases mercury that bioaccumulates in fish. Indigenous communities eating contaminated fish show neurological symptoms. The river carries poison downstream. Traditional food becomes toxic.
The liquid metal's path
In the remote regions of the Brazilian Amazon, illegal gold mining operations, known as garimpos, introduce elemental mercury into the environment. Miners mix liquid mercury with dredged river sediment to form an amalgam with tiny gold particles. This mixture is then heated, vaporizing the mercury to leave behind the gold. This process releases hundreds of tons of mercury into the atmosphere and directly into river systems like the Jauaperi.
Once in the water, the elemental mercury stays in the water. Anaerobic bacteria in the sediment convert it into a far more dangerous compound: methylmercury (MeHg). This organic form of mercury is highly neurotoxic and readily absorbed by living organisms. It enters the base of the aquatic food web through microorganisms and moves up the food chain. Methylmercury bioaccumulates, meaning organisms absorb it faster than they can excrete it. As smaller fish are eaten by larger ones, the concentration of the toxin becomes magnified at each successive trophic level.
A poisoned diet
For the indigenous and riverine communities who depend on the river for sustenance, this process of biomagnification has made a dietary staple toxic. Predatory fish, which are often a preferred food source, accumulate the highest concentrations of methylmercury. Species such as the peacock bass (Cichla ocellaris), wolf fish (Hoplias malabaricus), and large catfish can have mercury levels far exceeding the 0.5 micrograms per gram limit recommended by the World Health Organization (WHO). In some studies of Amazonian rivers, certain carnivorous fish have shown mercury concentrations as high as 2.64 micrograms per gram.
The constant consumption of contaminated fish leads to chronic mercury exposure. Studies on indigenous groups like the Yanomami and Munduruku show alarming results. Hair samples, a common biomarker for long-term mercury exposure, have revealed levels many times higher than the WHO's upper safe limit of 6 micrograms per gram. Some communities show average concentrations well over 20 µg/g. The health consequences are severe. Symptoms of mercury poisoning include cognitive disorders, loss of coordination, vision and hearing problems, and tremors. The exposure is particularly dangerous for fetuses and young children, as methylmercury can cross the placental barrier and affect brain development, leading to irreversible neurological damage.
💡Fun Facts
Methylmercury, the form that accumulates in fish, is significantly more toxic to humans than the elemental mercury used by miners.
Up to 96% of the total mercury found in Amazonian predatory fish can be in the form of methylmercury.
It is estimated that for every kilogram of gold extracted via this method, miners release a significant amount of mercury into the ecosystem.
Mercury is a persistent element; it does not break down and can cycle between the water, soil, and atmosphere for long periods.