The high price of gold

Mercury initially leaves no visible traces. In its most dangerous form for humans and animals, it is odorless, does not discolor water, and is almost impossible to taste. This heavy metal travels with rivers, where microorganisms convert it into methylmercury, which then accumulates along the food chain. In this way, it ultimately ends up on the plates of people who depend on the rivers for their livelihoods.

Mercury occurs naturally in low concentrations – including in the Amazon region. However, in many and increasingly more areas, environmental mercury levels are being significantly elevated by illegal gold mining. There, the metal is used to extract even the finest gold particles from river sediments, allowing it to enter rivers and soils.

A new study has, for the first time, systematically measured the extent of mercury exposure among people in Loreto, a region in northern Peru where FZS is also active. The results are cause for concern – and point to serious consequences for the health and food security of affected communities.

Majority of participants in the critical range

The study was conducted by the Centro de Innovación Científica Amazónica (CINCIA) under the leadership of environmental scientist Claudia Vega, together with FZS in Peru. Hair samples from more than 430 people from nine communities in the catchment areas of the Nanay, Pintuyacu, and Putumayo rivers were analyzed. Hair samples are internationally recognized as a reliable biomarker for long-term exposure to methylmercury, the organic and particularly toxic form of mercury. To ensure robust and meaningful results, the research team combined these data with fish and sediment samples from the river systems.

Exposure far above recommended limits

Around the Nanay and Pintuyacu rivers, the average mercury concentration was 8.41 milligrams per kilogram of hair, and at the Putumayo it reached 15.67 milligrams, with peak values exceeding 50 milligrams. A large proportion of the population studied therefore clearly exceeds the joint recommendation of the World Health Organization (WHO) and the Food and Agriculture Organization (FAO) of a maximum of 2.2 milligrams per kilogram, above which health risks can no longer be ruled out. These levels indicate that affected individuals have been exposed to the toxin over an extended period.

Pregnant women and children are particularly at risk. In the Putumayo catchment area, the analysis shows that 81 percent of women of childbearing age are exposed to this elevated health risk.

“These figures do not represent abstract exposure – they represent real people,” says Claudia Vega. “Methylmercury can attack the central nervous system, meaning the brain and spinal cord, including in unborn babies. The consequences are severe and can last a lifetime.”

The poison from gold mining

According to the World Health Organization, mercury is one of the most dangerous environmental toxins. The contamination in Loreto is a local symptom of a global problem: the rising demand for gold. High gold prices are attracting more and more gold miners, and nearly half of the gold in Peru is extracted illegally. Due to a lack of effective controls and the rarity of penalties, the gold rush in the Peruvian rainforest continues largely unchecked.

“Every gold ring has a story,” says Vega. “Many consumers do not know where their gold comes from – and that it may have been mined illegally, poisoning people and biodiversity in the Amazon, the world’s largest tropical rainforest.”

This is also confirmed by fish samples from rivers and local markets. Large predatory fish in particular, which absorb the heavy metal through their prey, show high levels of contamination. For many Peruvians living along the rivers, fish is the main source of protein and an essential part of their diet.

“The tragedy,” Vega explains, “is that many communities are not involved in gold mining themselves. They bear the consequences of destruction that begins elsewhere and reaches them through the rivers.”

Pollutants reach remote regions

The Amazon region is vast and highly interconnected. Pollutants often travel hundreds of kilometers, reaching even remote protected areas. In the Yaguas–Putumayo region, FZS has been supporting conservation efforts for years. A strategically important ranger post in Yaguas National Park is intended to help detect and prevent illegal activities at an early stage.

“Our rangers are the eyes and ears of the region,” explains Claus Garcia, FZS coordinator for the Yaguas–Putumayo landscape and co-author of the study. “After dredging vessels were discovered within the protected area, park management is now coordinating measures with authorities to remove them. We are concerned about how this external pressure is increasing. Without a presence on the ground, protected areas – which serve as refuges for many species – would quickly be lost.”

Problem across the entire Amazon

The study builds on earlier research from the Colombian Amazon, which has also documented elevated mercury levels in both people and fish. One of these studies was conducted by FZS together with Indigenous communities in the region (see GORILLA 1/2025). Together, these findings paint a clear picture: in many parts of the Amazon, mercury is a silent threat to both people and nature. And it is spreading – carried by rivers all the way to the oceans.

For FZS, protecting biodiversity is inseparable from protecting local communities. “Conservation does not end at the borders of a national park,” says Garcia. “If rivers are poisoned, the entire system suffers: ecosystems as well as the people who depend on them.”

The study from Peru provides a scientific basis to raise greater awareness of this issue. It highlights the urgent need for stronger controls against illegal gold mining, greater international responsibility, and long-term support for protected areas. For the people of the Amazon, it is not only the future of their environment that is at stake, but also that of their children.

– by Anja Schuller.