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What’s the Issue: Methylmercury Exposure

Exposure to mercury affects the immune system, alters genetic and enzyme systems, and damages the nervous system, including coordination and the senses of touch, taste, and sight (1). Methylmercury is the most toxic form of mercury. People are exposed to methylmercury almost entirely by eating contaminated fish that are at the top of aquatic foodchains (2) 

Research to Practice: Ecosystem Research to Characterize Methylmercury Exposure Routes in the Amazon 

Regional increases of mercury levels in fish were generally thought to be directly attributable to mercury releases from local gold mining operations. However, an extensive three year study, conducted from 1994-1997 along the Tapajós River basin, shed new light on the question (3). These studies demonstrated that mercury from mining operations contributed only a small percentage of the total mercury found in the river (4).



As with any of the chemical elements, mercury exists naturally as part of the Earth and over time, the ultimate sink for mercury is in the sediments of the Earth's oceans and lakes (5). The scientists linked high mercury concentrations with the initiation of slash-and-burn agriculture, a common practice in the Amazon today. By removing trees, loggers and 'slash and burn' farmers unearth naturally occurring mercury deposits bound to soil particles and rains wash this mercury rich soil into nearby water ways where it is converted to methyl mercury (a form easily taken up by fish and humans).

Researchers established a close relationship with the community to educate community members about the risks of eating different fish species through posters depicting methylmercury concentrations in different types of fish. Local residents also began to change agricultural techniques. In a joint initiative with researchers, small farmers identified the crops that could improve diets and reduce the intake of mercury (6). The researchers also worked with local fishermen to identify the stretches of river that would have lower methylmercury levels and be safest for fishing.

These interventions based on scientific evidence and carried out in collaboration with the local community have produced concrete results: from 1995 to now, measured mercury levels in local residents dropped significantly (7)

What’s Next? Further Research on Ecosystem Health and its links to Human Health

Further research that examines the links between ecosystem and human health is vital to understand environmental determinants of human diseases. The rapid economic development and urbanization of countries in the Latin American and Caribbean region are exacerbating a whole host of emerging and re-emerging environmental health threats. The World Health Organization estimates that worldwide, 13 million deaths could be prevented every year by making our environments healthier (8).

For more information on environmental health visit the PAHO Sustainable Development and Environmental Health Website

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(1) Edna M Yokoo, Joaquim G Valente, Lynn Grattan, Sérgio Luís Schmidt, Illeane Platt and Ellen K Silbergeld. 2003. Low level methylmercury exposure affects neuropsychological function in adults.Environmental Health: A Global Access Science Source 2:8.

(2) USGS Factsheet.

(3) IDRC Research Program Case Studies.

(4) René Canuel, Marc Lucotte and Sylvie Boucher de Grosbois. 2009. Mercury cycling and human health concerns in remote ecosystems in the Americas. S.A.P.I.EN.S, 2.1. Link

(5) Wheeler, M. 1996. Measuring Mercury. Environmental Health Perspectives 104:8. Link.   

(6) Lebel, J. 2005. Salud: um enfoque ecosistémico. Bogotá: Alfaomega.

(7) Ibid.

(8)WHO Environmental Health:


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