Study Finds High Levels of Mercury in Hair Samples From Indigenous Women in Peru and Nicaragua
Study Finds High Levels of Mercury in Hair Samples From Indigenous Women in Peru and Nicaragua Small-scale gold mining in the area releases mercury into the environment, where it can make its way into fish and, in turn, humans Sara Hashemi - Daily Correspondent October 14, 2025 1:05 p.m. A gold mining operation in Peru IPEN Women in Indigenous communities living near artisanal and small-scale gold mining operations in Peru and Nicaragua have high levels of mercury in their hair, a new analysis suggests. Researchers say the finding illustrates the dangers of small-scale mining worldwide. A new report published October 14 by the International Pollutants Elimination Network (IPEN)—a coalition of non-governmental organizations dedicated to eliminating toxic chemicals—analyzed hair samples from 105 women of child-bearing age (18-44) in four Indigenous communities in Peru and two in Nicaragua. All lived along rivers close to gold mining operations, and fish was part of their diets. An analysis performed at the Biodiversity Research Institute in Maine found 88 percent of these women had mercury levels above the United States Environmental Protection Agency’s 1 ppm threshold for adverse effects from mercury in a developing fetus. All but one had levels above 0.58 ppm, a stronger threshold proposed by a variety of environmental organizations based on research linking low levels of mercury exposure to brain damage to fetuses. The researchers attribute the high mercury levels in the women’s hair to small-scale gold mining. Pollution caused by the practice is a growing problem globally, and Indigenous communities face the brunt of its impact. These mining operations use mercury to extract gold: Miners dredge gold from soil or river sediment and mix in mercury to form a hard coating around the metal. This mercury-gold amalgam is then burned, leaving behind the coveted gold, while mercury is released into the environment. Key concept: Mercury in fish Though nutrition experts tout fish as a healthy food, chowing down could get you sick due to high mercury levels in some fish. The EPA advises people to eat primarily from a list of healthier seafood including anchovy, herring, lobster and salmon and avoid the fishes with the highest mercury levels: king mackerel, swordfish, shark, bigeye tuna, orange roughy, marlin and tilefish. “The rivers are becoming contaminated as a result of the mercury use and gold extraction,” Lee Bell, the lead author of the study and IPEN’s mercury and persistent organic pollutants policy advisor, tells Smithsonian magazine. “You’ve got food chain contamination, and Indigenous people are heavily reliant on fish from the rivers in the Amazon basin as their main dietary protein source,” he adds. “They have very little say in the impacts that are occurring, and there’s very little redress for them under the current arrangements, both at national and international level, to preserve their human rights.” Though it’s naturally occurring in the environment, mercury acts as a neurotoxin in the human body. According to the World Health Organization, the element “is toxic to human health, posing a particular threat to the development of the child in utero and early in life.” Its impacts include nervous system damage, developmental and behavioral disorders, and kidney problems. The amount of mercury in hair is considered a reflection of a person’s blood concentration of mercury at the moment of hair growth. Hair samples are collected in Puerto Arturo, Peru. IPEN “The results from this sampling project clearly indicate that women of childbearing age in Peru and Nicaragua are being impacted by mercury contamination of their environments,” the researchers write in the report. The local effects of the contamination—and its associated impacts on child development within the community—“far outweigh the economic gain for the few miners who succeed in extracting significant amounts of gold,” they conclude. William Pan, a researcher at the Duke Global Health Institute who studies mercury contamination but was not involved in the new report, tells Smithsonian magazine that while the study further confirms that mercury pollution is a problem in Indigenous communities in South America, it has a serious limitation: the fact that the sampling was not randomized. Instead, the women were selected based on different criteria, including their willingness to participate. The 105 women in the study represented about 25 percent of the women in their communities. “Normally, you would say a 25 percent sample is pretty good. But since it wasn’t randomized, you can’t say it’s representative of those women,” Pan explains. “That’s not to say the mercury levels aren’t high, but I don’t know why they did not randomize.” Bell notes that because the Indigenous communities that participated in the study are small, randomizing their sample would have been difficult. But given that the community members shared similar diets on the same rivers, “it is unlikely that randomization would have produced much different results,” he adds. If governments were to conduct larger studies in the future, he agrees that randomization would play a role there. The Minamata Convention on Mercury is an international treaty adopted in 2013 that aims to protect human health and the environment against the impact of mercury. Currently, it does not prohibit the use of mercury in artisanal and small-scale gold mining operations. “Minamata is just not doing enough to address that problem,” Pan tells Smithsonian magazine. “I think you really need to tackle the main problem. Let’s just stop mercury. Let’s figure out how to stop that.” Marcos Orellana, an environmental lawyer and the United Nations special rapporteur on toxics and human rights who wrote the foreword to the report, also says the convention needs strengthening. “This may be a very good moment to think about ways to do that, now that the evidence keeps on mounting in regard to the gaps that hinder the Minamata Convention’s effectiveness when it comes to small-scale gold mining,” he tells Smithsonian magazine. The treaty’s governing body will meet in early November, and Bell says he hopes it bans the use of mercury in these mining operations, as well as the mercury trade. Get the latest stories in your inbox every weekday.
Small-scale gold mining in the area releases mercury into the environment, where it can make its way into fish and, in turn, humans
Study Finds High Levels of Mercury in Hair Samples From Indigenous Women in Peru and Nicaragua
Small-scale gold mining in the area releases mercury into the environment, where it can make its way into fish and, in turn, humans
Sara Hashemi - Daily Correspondent
Women in Indigenous communities living near artisanal and small-scale gold mining operations in Peru and Nicaragua have high levels of mercury in their hair, a new analysis suggests. Researchers say the finding illustrates the dangers of small-scale mining worldwide.
A new report published October 14 by the International Pollutants Elimination Network (IPEN)—a coalition of non-governmental organizations dedicated to eliminating toxic chemicals—analyzed hair samples from 105 women of child-bearing age (18-44) in four Indigenous communities in Peru and two in Nicaragua. All lived along rivers close to gold mining operations, and fish was part of their diets.
An analysis performed at the Biodiversity Research Institute in Maine found 88 percent of these women had mercury levels above the United States Environmental Protection Agency’s 1 ppm threshold for adverse effects from mercury in a developing fetus. All but one had levels above 0.58 ppm, a stronger threshold proposed by a variety of environmental organizations based on research linking low levels of mercury exposure to brain damage to fetuses.
The researchers attribute the high mercury levels in the women’s hair to small-scale gold mining. Pollution caused by the practice is a growing problem globally, and Indigenous communities face the brunt of its impact. These mining operations use mercury to extract gold: Miners dredge gold from soil or river sediment and mix in mercury to form a hard coating around the metal. This mercury-gold amalgam is then burned, leaving behind the coveted gold, while mercury is released into the environment.
Key concept: Mercury in fish
Though nutrition experts tout fish as a healthy food, chowing down could get you sick due to high mercury levels in some fish. The EPA advises people to eat primarily from a list of healthier seafood including anchovy, herring, lobster and salmon and avoid the fishes with the highest mercury levels: king mackerel, swordfish, shark, bigeye tuna, orange roughy, marlin and tilefish.
“The rivers are becoming contaminated as a result of the mercury use and gold extraction,” Lee Bell, the lead author of the study and IPEN’s mercury and persistent organic pollutants policy advisor, tells Smithsonian magazine.
“You’ve got food chain contamination, and Indigenous people are heavily reliant on fish from the rivers in the Amazon basin as their main dietary protein source,” he adds. “They have very little say in the impacts that are occurring, and there’s very little redress for them under the current arrangements, both at national and international level, to preserve their human rights.”
Though it’s naturally occurring in the environment, mercury acts as a neurotoxin in the human body. According to the World Health Organization, the element “is toxic to human health, posing a particular threat to the development of the child in utero and early in life.” Its impacts include nervous system damage, developmental and behavioral disorders, and kidney problems. The amount of mercury in hair is considered a reflection of a person’s blood concentration of mercury at the moment of hair growth.
“The results from this sampling project clearly indicate that women of childbearing age in Peru and Nicaragua are being impacted by mercury contamination of their environments,” the researchers write in the report. The local effects of the contamination—and its associated impacts on child development within the community—“far outweigh the economic gain for the few miners who succeed in extracting significant amounts of gold,” they conclude.
William Pan, a researcher at the Duke Global Health Institute who studies mercury contamination but was not involved in the new report, tells Smithsonian magazine that while the study further confirms that mercury pollution is a problem in Indigenous communities in South America, it has a serious limitation: the fact that the sampling was not randomized. Instead, the women were selected based on different criteria, including their willingness to participate.
The 105 women in the study represented about 25 percent of the women in their communities. “Normally, you would say a 25 percent sample is pretty good. But since it wasn’t randomized, you can’t say it’s representative of those women,” Pan explains. “That’s not to say the mercury levels aren’t high, but I don’t know why they did not randomize.”
Bell notes that because the Indigenous communities that participated in the study are small, randomizing their sample would have been difficult. But given that the community members shared similar diets on the same rivers, “it is unlikely that randomization would have produced much different results,” he adds. If governments were to conduct larger studies in the future, he agrees that randomization would play a role there.
The Minamata Convention on Mercury is an international treaty adopted in 2013 that aims to protect human health and the environment against the impact of mercury. Currently, it does not prohibit the use of mercury in artisanal and small-scale gold mining operations.
“Minamata is just not doing enough to address that problem,” Pan tells Smithsonian magazine. “I think you really need to tackle the main problem. Let’s just stop mercury. Let’s figure out how to stop that.”
Marcos Orellana, an environmental lawyer and the United Nations special rapporteur on toxics and human rights who wrote the foreword to the report, also says the convention needs strengthening. “This may be a very good moment to think about ways to do that, now that the evidence keeps on mounting in regard to the gaps that hinder the Minamata Convention’s effectiveness when it comes to small-scale gold mining,” he tells Smithsonian magazine.
The treaty’s governing body will meet in early November, and Bell says he hopes it bans the use of mercury in these mining operations, as well as the mercury trade.