Traces of mercury have reached the most remote areas of the Colombian Amazon

It’s no surprise that the Amazon region is poisoned by mercury. In the region that’s fighting to remain humanity’s greatest asset against climate change, there are at least 2,312 sites and 245 areas where illegal mineral extraction takes place. This according to data from the Amazon Network of Georeferenced Socio-Environmental Information (RAISG).

From these sites, we know that mercury is being released into the environment. And, from that point, it begins a long journey. As data recently published by the Frankfurt Zoological Society (FZS) in Colombia shows, the chemical element passes through Indigenous communities in areas that are considered remote, and aren’t necessarily surrounded by mining.

“Mercury is very volatile; its dynamics are broader than people think,” says Esperanza Leal Gómez, director of the FZS in the South American country. After taking a look at more than 1,200 samples of fish from 2023 until February 2025 — which were collected by members of the Mocagua, El Itilla and La Victoria Indigenous reservations — the organization found that between 10% and 28% of the species analyzed had mercury concentrations above World Health Organization (WHO) recommendations. A similar analysis had never been performed in these Amazonian communities, which are considered to be “remote,” benefiting from a certain degree of protection.

The Itilla River, for example, is located in the municipality of Calamar, in the southern-central department of Guaviare. It completely overlaps with Serranía de Chiribiquete National Park, at its northernmost point. La Victoria is located between that same protected area and the Yaigoje Apaporis National Park. Meanwhile, the Mocagua River passes through Amacayacu National Natural Park, on the Amazon River.

The initiative initially aimed to better explore fishing methods and species consumption in each community. The idea of measuring the mercury levels in fish emerged during the process. “They had that particular question, so we took the opportunity to introduce the discussion about contamination. Also, the more you depend on fishing for food security, the more exposed you are to contamination.”

The first samples were taken in the respective malocas, or communal houses. Yesid López Pinto — a hydrobiological resources consultant at the FZS — explains that the freshly caught fish were brought there. That way, everyone could observe how a “slice” of the fish was removed, tagged and stored. “It was essential that the communities be informed and, if necessary, be able to take samples,” he explains.

In the mornings, the team waited for the fishermen to arrive from their first outings. And, during the day, they also entered some homes with permission, to take fragments of the fish that the men had caught the previous night. The researchers then stored the samples and sent them to laboratories at the University of Cartagena and the University of Córdoba, in the north of Colombia.

The highest mercury levels were found in fish from La Victoria, while the lowest were found in Mocagua. What most intrigued the scientists, however, was the case of El Itilla. Of the three, it’s the reserve that’s furthest from any mining (at least, mining activities that have been identified) and yet, there are concentrations of mercury in the fish.

The FZS has a hypothesis: the Indigenous reservation is surrounded by an area that has faced significant deforestation. And the loss of trees — especially to fires — also releases mercury. “This relationship between vegetation loss and mercury isn’t something we’ve measured in this case, but it’s been reported in the literature,” says Leal, who still insists that this is an assumption. Finding a causal relationship would require further studies, as well as answering another question: how much mercury poisoning are the people living on the reservations experiencing?

What the researchers do know is that the species with the highest concentrations of mercury are indeed those that feed on other fish and are longer than 13 inches, such as piranhas, marlin, payara and corvina. And, although some are part of the regular diet on the reserves, they’re not the fish that are consumed the most.

“Fortunately, in the three areas where we work, [the residents] still eat a high number of different species, precisely because they haven’t lost their fishing skills,” Leal adds. What she means is that if fishing methods — such as diving or trapping techniques — are maintained, the diversity of captured species is greater. And, when a person eats food from different sources, they’re less exposed to mercury contamination. This is a kind of adaptive advantage that the Indigenous people of the Amazon possess.

The knowledge from this experience was reflected in a custom-made poster for each of the three reservations. It displays the sampled species and their mercury concentrations. They’re categorized similarly to a traffic light: those with high levels appear in red, those with medium levels appear in orange, while those with low mercury concentrations appear in green. “This isn’t to tell them what they can’t eat,” Leal emphasizes. Rather, it’s more like a reminder to keep in mind the range of options offered by the Amazonian rivers.

Translated by Avik Jain Chatlani.

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