Research Profile - Understanding the ecology of health

A Canadian researcher studies nutrition, contaminants and biodiversity in the Amazon

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For many people that live near the Tapajós River, a major tributary of the Amazon River, the body of water is more than just a part of their landscape. It is their highway, their livelihood and their main source of food. And it is affecting their health

In 1994, researchers in Brazil asked Dr. Donna Mergler, a neurotoxicologist, and Dr. Marc Lucotte, a biogeochemist, from the Université du Québec à Montréal to come down to the Tapajós River to help investigate whether the health of people living in fishing villages along the river was affected by the high levels of mercury in their bodies. With funding from the International Development Research Centre, the researchers began to look for the source of the mercury and assess the villagers' health.

"Dr. Lucotte's team found that deforestation was the source of the mercury," says Dr. Mergler. "There's mercury naturally in the soil, and when you take away the forest cover, soil erosion increases and the soil goes into the water, where it is transformed into organic mercury, enters the food chain and accumulates in the fish."

This contamination of the fish population was a big problem for the riverside communities, which rely on fish as a main source of food. They also ate more predator fish – those at the top of the food chain – which have the highest levels of mercury contamination.

Dr. Mergler and her team recorded the types and quantity of fish that the villagers ate and collected hair samples to see how their mercury levels changed. This way, the researchers were able to identify which fish species were contributing the most mercury to the villagers' diets. They then tested the villagers' nervous system and cardiovascular functions to see if the mercury was affecting their health.

"For example, we looked at motor coordination, fine motor movement and vision, and we found that higher one's mercury level, the poorer their performance on tests that evaluate these skills," says Dr. Mergler. "The person does not necessarily have a clinical disorder, but if you are a fisherman that needs to repair your net, the fact that you are losing motor coordination, fine movement and vision is very important."

In the next stage of the project, Dr. Mergler and her team worked with the villagers to find ways to reduce their exposure to mercury while still keeping fish on the menu. They developed an educational campaign and slogan: "Eat more fish that don't eat other fish."

Five years after the introduction of the slogan, Dr. Mergler found that the villagers were eating more herbivores (fish that eat only plants), the mercury levels in their hair had decreased, and their motor skills were improving. Acting on a question posed by one of the villagers during a workshop with women on nutrition and health, the researchers decided to study other aspects of the villagers' diet, to see if something else might be influencing mercury levels.

"This is a little village of about 550 people, in the middle of the Amazon, only accessible by boat at the time – and everyday for an entire year 26 women wrote down everything that they ate," recalls Dr. Mergler. The activity was coordinated by the village mid-wife, who ensured that the questionnaires were filled out daily. At the end of the year, the researchers analyzed the villagers' hair again and discovered that those who were eating a lot of fruit had lower mercury levels, even if they also ate a lot of fish.

But even as their mercury levels fell, the villagers' vision failed to improve. At this point, the research team received funding from the Canadian Institutes of Health Research (CIHR) to look more closely at what was happening with the visual system of 450 persons from 12 riverside villages. Their findings confirmed the negative effects of mercury on several visual functions, but they also discovered that selenium, whose major source was Brazil nuts, seemed to offset some of the visual damage caused by mercury exposure.

Dr. Carlos Passos, who joined the Tapajós project as a Brazilian undergraduate student, feels that the project illustrated the importance of taking a broad, multidisciplinary view of the environment to solve a complex health problem. "While conducting investigations into the potential protective effects of local Amazonian fruit consumption in preventing exposures to methyl mercury via dietary fish intake, I could see the advantages of applying the principles of an eco-health approach in order to maintain an ecosystem's integrity and improve human health," says Dr. Passos. "Such experiences have been of great usefulness in our current research activities on the Tapajós."

The work of Dr. Mergler and her colleagues has now inspired a Teasdale-Corti project to work with local farmers to reduce slash and burn deforestation and stop the mercury contamination at its source. The project will work with farmers to move away from traditional agricultural practices, which speed up the erosion process, and start growing local grains and trees to help preserve the soil.

"By taking an ecosystem approach and linking all of these ideas together, we're trying to figure out how one can use the tremendous biodiversity of the Amazonian environment to foster good nutrition, reduce toxic risk and improve human health," says Dr. Mergler.