PUERTO MALDONADO, Peru—On a busy, dusty street beside a huge open-air market, signs reading “oro” mark shops that trade in gold. The customers, mostly men in work clothes and rubber boots, have just arrived from the mining camps to sell their gold and wire money home.

Inside, shopkeepers heat the miners’ clumps of gold ore, releasing mercury vapors that waft into the shop, and then outside, into the streets crowded with townspeople.

Experts have long known Peru’s miners are exposed to extremely high levels of mercury. But now new research shows that the toxic threat has spread to towns in the Amazon and Andes Mountains where gold is sold.

In Puerto Maldonado, a jungle town in Madre de Dios, one of Latin America’s most productive gold mining areas, researcher Luis Fernández in 2009 detected mercury levels at a gold shop that were more than 20 times higher than an international worker safety standard. This February, his follow-up testing found mercury levels inside one shop that were so extreme his monitor couldn’t measure them.

Then, a week later, in a town high in the Andes, Fernández became truly alarmed when he measured mercury in the air outside the gold shops, and detected levels that exceeded the amounts considered safe.

“It seems clear that these workers are under extraordinary risk for acute mercury poisoning,” he said, adding that people outside the shops are highly exposed, too.

In the first study of its kind in Peru, Fernández and a team of researchers funded by the U.S. Environmental Protection Agency are measuring mercury pollution from gold shops in Puerto Maldonado, in the Amazonian lowlands, and La Rinconada, 15,000 feet above sea level in the Andes Mountains.

Their initial findings—coupled with new tests by Peru’s National Institute of Health that measured mercury in people’s urine—point to a public health risk in towns near informal mining camps, which have flourished with skyrocketing international gold prices.

Elemental mercury—the type released into the air and inhaled at the shops—can damage the nervous system, causing tremors, memory loss, muscle weakness and twitching, irritability, insomnia, headaches and reduced mental abilities. It also has been linked to immune system disorders in Brazilian miners. Extremely high levels can be deadly.

Peruvian officials estimate that there are 100,000 small-scale miners working in virtually every region of Peru, so gold-shop emissions are a widespread problem.

If La Rinconada and parts of Madre de Dios were in the United States, they “would most likely be Superfund sites,” said Fernández, a field lab research associate at the Carnegie Institution for Science’s Department of Global Ecology, located at Stanford University.

Gold mining is a dirty, dangerous business. Most of Madre de Dios’ 20,000 miners are “informal,” working without contracts, under hazardous conditions and with no safety equipment. Officially, the region produces about 20 tons of gold a year, although the real amount is probably higher because most of the mining is unregulated.

Working in far-flung camps along rivers or in the rain forest, laborers mix sediment with mercury – often using their hands and feet – to amalgamate the gold. But health experts say the greatest hazard comes from inhaling the vapor during reheating of the amalgam in the field or in shops with a flame or torch. Fernández estimates that between 2 and 5 percent of the weight of those lumps is mercury.

Dr. Carlos Manrique, who heads the Madre de Dios regional health department’s epidemiology office, said he saw miners with tremors, headaches and gastrointestinal problems – all possible symptoms of mercury poisoning – when he worked at the health clinic in Huepetuhe, a mining town about 100 miles from Puerto Maldonado. The river there is so silted from mining that trucks now drive on it.

“But I had no way of knowing if the symptoms were really due to mercury poisoning, because we don’t have equipment” for analysis, Manrique said.

No one has done a health assessment of Peru’s miners or townspeople to check for symptoms of mercury poisoning.

But a new study raises concerns. While most urine samples collected from about 200 people in Huepetuhe last year showed mercury levels below the World Health Organization limit for occupational exposure, a few were extremely high, according to Dr. Jonh Astete, who coordinated the study by Peru’s National Institute of Health.

Astete said some of the highest mercury levels were in people who were not directly involved in mining, but who lived near places where gold is bought and sold, such as the shop where the emissions were too high to be measured by the EPA’s gauge.

Every mining town has gold shops, all emitting mercury. About a dozen of these shops are clustered in less than two blocks across the street from Puerto Maldonado’s open-air market, the town’s main shopping area. In addition, officials say there are at least eight shops elsewhere in town, and some people probably process gold clandestinely in their homes.

Working under metal hoods with no filters, the shopkeepers heat the gold to vaporize the mercury before paying miners. During the burning, which takes several minutes, shop employees and customers are exposed to high doses of mercury vapor. Some shops have pipes leading outside, so the vapor spills into the air above the heads of shoppers passing by, near the windows of nearby low-budget hotels.

During a pilot study in 2009, Fernández found one shop in Huepetuhe where mercury averaged 450 micrograms per cubic meter of air—22 times higher than the World Health Organization’s occupational health standard — with spikes as high as 1,000.

Working with Argonne National Laboratory, the researchers devised a simple filter made of a barrel fitted with metal baffles and a fan, which local metalworkers can fashion for about $500. After a filter was installed in the shop, the levels dropped to about 40 micrograms per cubic meter, twice the international standard.

When the EPA team, headed by Marilyn Engle of the EPA’s Office of International Affairs, returned to Puerto Maldonado in February, they found that several other shops had installed similar, locally made filters. Their study will analyze the filters’ effectiveness.

As bystanders watched curiously, the EPA team set up metering equipment in black cases resembling portable speakers on the sidewalk outside shops. Donning respirators, they gave shop employees individual meters to wear for a work shift, then inserted tubes and traps into the hoods to measure elemental and gaseous mercury.

The team will use those data not only to calculate shop emissions, but also to model dispersion of airborne mercury.

Worldwide, informal mining like that in Madre de Dios releases between 650 and 1,000 tons of mercury a year into the air and waterways, according to the UN Environment Programme.

The threat is even more acute in La Rinconada, a one-time mining camp in the Andes that has grown into a town of about 40,000, with more than 200 gold shops. While miners in the Amazonian lowlands separate gold flecks from river sediment, those in La Rinconada drill ore from the mountains, then use huge grindstones to crush it with mercury.

They take the entire amalgamated mass – which Fernández said could weigh as much as a kilogram, half of which is mercury – to a shop for burning. Because of the mass, the process can take half an hour or more, exposing shop workers and customers to higher mercury levels for a longer time than in the shops in Puerto Maldonado.

In near-freezing temperatures, the vaporized mercury condenses quickly, precipitating into gutters and onto the street, and even pooling on the floor of shops or adjoining living quarters, Fernández said.

He said the risk of acute mercury poisoning for La Rinconada's shop owners is "extraordinary."

The droplets of elemental mercury are not as risky to developing fetuses as the form of mercury that is found in fish. They pass from the lungs into the bloodstream and are carried throughout the body, but they do not cross the placenta, according to Jennifer Nyland, assistant professor in the Pathology, Microbiology and Immunology Department at the University of South Carolina School of Medicine.

Nevertheless, much of the mercury vapor eventually precipitates out or dissolves in rain and washes into streams or rivers.

In waterways, bacteria convert elemental mercury to methylmercury, an organic form that accumulates in food chains, increasing in concentration higher up the chains. As a result, even people who do not live near gold shops are exposed to the mercury when they eat fish.

Humans are at the top of the food chain, and about 300 tons of fish a year are sold in the markets in Madre de Dios – not counting those caught by residents of indigenous communities along rivers near mining camps.

Adults, children and fetuses are at risk, because unlike inhaled mercury vapor, methylmercury can cross the blood-brain barrier and the placenta.

“The developing fetus is probably most sensitive to methylmercury,” said Donna Mergler, principal investigator of the Canadian Institutes of Health Research, who has studied mercury in Brazilian Amazonian communities in which fish is a dietary mainstay.

Methylmercury consumption is linked to decreases in IQ in children as well as neurodevelopmental problems.

In late 2009, Fernández tested tissue from 11 species of fish sold in the Puerto Maldonado market, finding mercury levels higher than the World Health Organization recommended maximum of 0.5 ppm in three of the most common fish. Studies in 2010 by Peru’s Ministry of Production had similar findings.

In Peru, the National Institute of Health’s urine samples reflect elemental mercury – mainly vapor inhaled within the past several days – but not methylmercury accumulated in human tissue, which shows up in blood or scalp hair.

Last year, working with a local doctor, Stanford University graduate student Katy Corrigan Ashe took hair samples from residents of Puerto Maldonado and several mining communities. She has just begun to analyze the samples, but has found levels above WHO’s occupational health limits in some people in Puerto Maldonado who are not miners.

Fernández plans to begin a new phase of the study of mercury in fish in Madre de Dios later this year. In addition, Peru’s National Institutes of Health will expand its study of mercury in miners and other residents to other communities along the Madre de Dios River.

In January, Manrique, the epidemiology director, was sworn in as a member of the Madre de Dios regional government council. He says he ran for office because he believed he had done as much as he could as a doctor, and that political leaders must solve the region’s health problems.

“Mercury poisoning is a problem that isn’t visible,” he said. “Local authorities still don’t realize how serious it is.”

This article originally ran at Environmental Health News, a news source published by Environmental Health Sciences, a nonprofit media company.