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.