Major Findings

Mercury in Fish

60% of the species of fish sold in in Puerto Maldonado had mercury levels that exceeded international mercury concentration limits for fish. Mercury levels of 9 of the 15 most consumed fish species had average levels of mercury above the international mercury reference limit (0.3 ppm).

Carnivorous fish species located high on the food chain had the highest mercury levels while species lower on the food chain had the lower mercury concentrations. Fish raised in the growing industry of fish farms generally had low mercury concentrations (figure 1).


Mercury levels increased in 90% of fish species between 2009 and 2012. Average mercury levels increased in 10 of 11 (90%) fish species analyzed between 2009 and 2012 including in species with mercury concentrations below the international mercury reference limit indicating that the aquatic ecosystems, the rivers and lakes in which these fish live, are increasingly impacted by mercury released by artisanal gold mining activity in Madre de Dios.


Mercury In Humans

78% of adults in Puerto Maldonado had hair mercury concentrations above international mercury reference limits for human hair. More than three out of four adults analyzed in Puerto Maldonado had mercury concentrations higher than the reference limit. Average mercury concentrations of adults were 2.7 ppm – almost three times the reference value of 1ppm (figure 2). Mercury levels in human hair ranged from 0.02 ppm to a high of 27.4 ppm, a level more than 27 times the international limit for mercury in human hair.


The most vulnerable population, Women of Child Bearing Age, had the highest average mercury levels. Women of child bearing age (between 16-49), a group most at risk from the neurotoxic effects of mercury, had the highest hair mercury levels of adults in Puerto Maldonado with average levels of 3.0 ppm (figure 2, red column). Women of child bearing age are particularly at risk because mercury can be passed to the developing fetus across the placental barrier and cause severe and permanent neurological damage to the unborn child.


The human population of Puerto Maldonado has a very high risk of mercury exposure and associated heath effects due to high consumption of local contaminated fish, experience in gold mining, and from inhalation of airborne mercury from gold buying shops. The majority of participants (92%) in Puerto Maldonado reported that they consume local river and lake fish regularly. 64% of respondents said they consume at least one high mercury species weekly, while 25% eat two or more on a weekly basis. Occupational exposure is also an important factor, as 25% of adults report working directly in gold mining. Lastly, the study results indicate that another significant exposure source of mercury exists in Puerto Maldonado and is contributing to the extremely high levels of mercury found in the adults of Puerto Maldonado. Suspected sources are the gold buying shops located in the center of Puerto Maldonado that release large amounts of mercury vapor, exposing thousands of people daily to toxic air levels.