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Mercury from gold mining contaminates Amazon communities’ staple fish

  • The four species of fish most commonly consumed by Indigenous and riverine people in the Brazilian state of Amapá contain the highest concentrations of mercury.
  • In some species, researchers found levels of mercury four times in excess of World Health Organization recommendations.
  • The mercury comes from gold-mining activity, where it’s used to separate gold from ore before being burned off and washed into the rivers.
  • The health impacts of mercury contamination are well-documented, and include damage to the central nervous system, potentially resulting in learning disabilities for children and tremors and difficulty walking for adults.

For the communities of the Amazon, a land defined by its rivers, fish has always been an important part of the diet. In the northern reaches of the Amazon, the top four species are tucunaré, pirapucu, trairão and mandubé.

But small-scale gold mining has turned these fish into an often deadly health hazard. According to a study published in July in the International Journal of Environmental Research and Public Health, mercury levels found in pirapucu (Boulengerella cuvieri) were four times higher than the safe limit established by the World Health Organization (WHO).

The researchers analyzed 428 samples of fish caught between 2017 and 2018 in five rivers in the Brazilian state of Amapá. The collection points were close to potential mining areas, where mercury is often used to separate gold from ore. The result: detectable levels of mercury were found in all samples. In 28.7% of them, the amount exceeded the WHO limit.

The study — a joint effort by the Oswaldo Cruz Foundation (Fiocruz), WWF Brazil, the Amapá Institute for Scientific and Technological Research (IEPA) and the Institute for Indigenous Research and Training (Iepé) — reveals the risks to which the state’s Indigenous and riverine populations are exposed, especially children.

To collect fish samples, the researchers traveled along remote rivers such as the Oiapoque and Araguari, near Brazil’s border with French Guiana. Image courtesy of Iepé.

Study co-author Paulo Basta, a medical doctor and researcher at Fiocruz, a scientific institution in Rio de Janeiro, says the impacts of mercury exposure on unborn children are already well-documented. These children “may face intelligence quotient impairments that will last throughout their lives,” he says. “They will have learning difficulties and fewer chances of getting good jobs and income. The result is a permanent cycle of inequality and poverty.” In the most severe cases, the child may be born with deformities.

In adults, mercury contamination may lead to coordination problems such as difficulty walking and hand tremors, hearing and vision impairment, and even dementia, Basta says.

Iepé assistant executive director Décio Yokota, another co-author of the study, says fish from the area studied is consumed by people from at least four Indigenous territories: Wajãpi, Uaçá, Juminã and Galibi. For these populations, fish is the main source of protein and also the main vector of mercury contamination as a result of bioaccumulation. “Small fish eat the algae, then a bigger fish eats the small fish and is eaten by other, even bigger, fish,” he says. “That’s why the most contaminated fish are usually at the top of food chains. They accumulate a very large amount of mercury in the process.”

This explains why carnivorous fish had the highest levels of contamination in the study: 77.6% of them had mercury above the WHO limit. “If you eat these contaminated fish every day, you increase your level of contamination each time you eat them,” Basta says.

The proportion contaminated with unsafe levels of mercury was 20% among omnivorous fish, which feed on both fish and plants, and 2.4% among herbivorous fish. The study authors recommend eating a maximum of 200 grams (7 ounces) of carnivorous fish a week. In the case of mandubé (Ageneiosus inermis), pirapucu, tucunaré (Cichla monoculus) and trairão (Hoplias aimara), consumption should be restricted to once a month.

Tucunaré (Cichla monoculus) collected during research. As a carnivorous fish at the top of the food chain, it accumulates the highest concentration of mercury. Image courtesy of Iepé.

Yokota acknowledges that it isn’t easy for people who rarely have other sources of protein to follow the recommendation. “Ideally, mining should be eliminated. If that’s not possible, we need to think about changing our diet. But we cannot tell people who have no other source of protein not to eat fish. That’s why we suggest that they try to eat more herbivorous fish, whose levels of contamination are much lower.”

A 2014 report shows mining is the main cause of deforestation in the Guiana Shield, a ​​2.5-million-square-kilometer (965,300-square-mile) area that straddles part of northern Brazil, French Guiana, Suriname, Guyana and part of Venezuela. It’s a long-standing problem that has gotten worse in recent years, according to Marcelo Oliveira-da-Costa, a WWF Brazil conservation expert and co-author of the new study. “Managers of Amapá’s conservation units say law enforcement has not been effective, and the political signals sent by the federal government are terrible,” he says. “If you look at the Amazon as a whole, [mining] is only increasing.”

Oliveira says there’s an urgent need for studies on the impact of mercury contamination on the Amazon’s Indigenous peoples. “We know that people are contaminated in several areas, such as the Yanomami, the Munduruku … but what are the effects? There is no investment to study the effects of contamination on those populations,” he says.

To fill in this information gap, the same research institutions plan to carry out studies later this year to assess the impact of mercury on the health of Amapá’s riverine families and the Munduruku people in Pará state.

The researchers collected 428 fish samples from 18 different locations. The fish were caught by local fishermen hired for the study. Image courtesy of Iepé.

Banner image of a fish caught during one of the expeditions, courtesy of Iepé.

This story was first reported by Mongabay’s Brazil team and published here on our Brazil site on Aug. 17, 2020.


Hacon, S. D., Oliveira-da-Costa, M., Gama, C. D., Ferreira, R., Basta, P. C., Schramm, A., & Yokota, D. (2020). Mercury exposure through fish consumption in traditional communities in the Brazilian northern Amazon. International Journal of Environmental Research and Public Health17(15). doi:10.3390/ijerph17155269

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