Gold mining site in Guacamayo mining area. Many fish species sold in the markets of Madre de Dios contain high levels of mercury, 78 percent of adults have hair mercury concentrations above international mercury reference limits for human hair. Photo: Luis Fernandez

By Lacey Avery
28 May 2013

( – The Madre de Dios region in Peru is recognized for its lush Amazon rainforests, meandering rivers and rich wildlife. But the region is also known for its artisanal gold mining, which employs the use of a harmful neurotoxin. Mercury is burned to extract the pure gold from metal and ore producing dangerous air-borne vapors that ultimately settle in nearby rivers.

"Mercury in all forms is a potent neurotoxin affecting the brain, central nervous system and major organs," Luis Fernandez, an ecologist and research associate at the Carnegie Institution's Department of Global Ecology, told "At extremely high exposure levels, mercury has been documented to cause paralysis, insanity, coma and death."

However, mercury does not typically trigger dramatic immediate health effects, Fernandez continued. Instead it causes slow, insidious damage eventually resulting in reduction of life span and decreased quality of life.

Mercury is especially toxic to women of childbearing age, between the ages of 16 and 49. The toxin can be passed to the developing fetus across the placental barrier and cause severe and even permanent neurological damage to the unborn child. Although recognized as a major environmental health contaminant, the dangers of mercury are still actively debated in most mining regions in the Amazon.

"Because of the slow nature of the damage done by mercury, combined with the vague symptoms of early exposure, it is common that mercury contamination is overlooked, or, in many cases, actively denied as a real health threat," Fernandez said.

But mercury is a health threat, especially in Puerto Maldonado, the capitol city of Madre de Dios. In 2009, Fernandez and a team of scientists found that many fish species sold in the markets of Madre de Dios contained high levels of mercury.

The study, led by the Carnegie Institution for Science's Department of Global Ecology, prompted the organization to establish the Carnegie Amazon Mercury Ecosystem Project (CAMEP) in 2012. Directed by Fernandez, CAMEP is made up of eight Peruvian universities and non-governmental organizations with Carnegie scientists.

The organization followed up on the 2009 report with two new studies in 2013. The investigations found high mercury concentrations not only in most of the wild caught fish sold in markets in Puerto Maldonado, but also in residents.

From May to August 2012, researchers offered adults in Puerto Maldonado free mercury hair testing, the main method used to determine mercury exposure in humans. The 226 participants completed a survey requesting information about individual fish consumption and mercury exposure history.

Researchers also analyzed mercury concentrations in the muscle tissue of commonly consumed fish. Fifteen different species of fish were purchased from several markets in the city during August 2012. Both the hair and fish samples were analyzed for total mercury at a laboratory established at the Environmental and Computational Chemistry Group, University of Cartagena in Colombia.

Researchers found that 9 of the 15 most consumed fish species sold in Puerto Maldonado had average levels of mercury above the international mercury reference limit of 0.3 part per million (ppm). In addition, the average mercury levels increased in 10 of the 11 fish species from 2009 to 2012, indicating the aquatic ecosystems are frequently altered by mercury, most likely due to artisanal gold mining activity.

"Initially confined to areas around the main stem of the Madre de Dios River, mining has expanded into dozens of formerly pristine tributaries, rivers, streams and lakes all over the department of Madre de Dios," Fernandez explains.

Mercury contamination is not restricted to wildlife. Many native communities and remote rural populations rely on wild caught fish for protein. Based on the survey, 92 percent of participants reported that they consume fish caught from local rivers and lakes on a regular basis. Sixty-four percent of the adults consume at least one high mercury fish species each week.

The hair tests found that 78 percent of adults had hair mercury concentrations above international mercury reference limits for human hair.

The average mercury concentrations of adults were 2.7 ppm – almost three times the reference value of 1 ppm. Mercury levels in human hair ranged from 0.02 ppm to an alarming high of 27.4 ppm. Women of childbearing age, the most vulnerable group, had the highest hair mercury levels with average levels of 3.0 ppm.

In addition to the consumption of contaminated fish, 25 percent of the adults reported working directly in gold mining. Scientists believe the residents are exposed to the toxin from gold mining and the inhalation of airborne mercury in gold buying shops located in the center of the city.

"Gold shops boil off the mercury found in the amalgams that miners create in the mining areas and sell to gold merchants," Fernandez explains. "Recent studies of gold shops in Peru indicate that an average gold shop can emit as much mercury as a 100 megawatt coal fired power plant each year." [more]

Scientists discover high mercury levels in Amazon residents, gold-mining to blame



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