The Price of Gold.

Indians at Risk in French Guiana 

The Wayana Amerindians of French Guiana live along the Maroni River and depend upon its fish as a significant source of food. However, that food source may be threatened by gold mining operations upstream, which release mercury pollution into the river. French researchers investigating the effects of mercury pollution upon the Wayana have found that all the natives over 1 year of age who were tested were ingesting more mercury than recommended by the World Health Organization (WHO) in their traditional fish-based diet [EHP 109:449-456]. Nadine Frery, a researcher at the National Institute of Public Health Surveillance in Saint-Maurice, France, and colleagues from the University of Bordeaux also report that the mercury load appears to cause what are characterized as subtle neurologic effects on the population, especially on children.

According to Frery, gold mining activities have been responsible for important discharges of mercury into the environment. In the mercury amalgamation method, gold obtained from river sediments, soils, and groundwater rocks is separated from elemental mercury by open-circuit heating, an activity that discharges this volatile form of mercury into water and air. Mercury can then find its way into carnivorous fish in its highly toxic methylmercury form. Along the aquatic food chain, there is a bioamplification of metal concentrations, leading to very high concentrations in the top predators--including people, such as the Wayana.

Frery and colleagues conducted the studies over seven days in each of two seasons, March and November 1997. Those periods are marked by changes in diet, particularly as fish and game sources fluctuate seasonally. The investigators gathered data on 165 subjects, including fish consumption over a 1-14 day period. Each day, they made records of the fish consumed species, size, weight, and weight after evisceration and deboning. They also recorded the weight, sex, and age of the persons participating in each meal. The total weight of consumed fish allowed the scientists to calculate the daily amount of mercury ingested by the families. Hair sampling analysis was performed by Canada's Center of Toxicology of Quebec to measure the transfer of mercury from endogenous fish species to the human subjects.

Hair sampling revealed that 57% of the 165 people studied had mercury concentrations 2-3 times higher than the WHO safety limit of 10 micrograms per gram/liter. Furthermore, from their food alone all of the Wayana subjects over 1 year old received 6-9 times the International Programme on Chemical Safety's estimated daily human intake of total mercury of 6.7 micrograms per day. (This figure allows for both direct exposures sources, such as polluted drinking water, and indirect sources, such as fish in which mercury has collected.) Similar results occurred among riverside populations eating a fish-based diet in portions of the Amazon River basin in Brazil following a gold rush that began in the late 1980s.

Along with the dietary study, Frery and colleagues gave each child a neurologic examination and neurobehavioral development tests. The results of the tests showed a correlation between mercury concentrations and neurologic or behavioral deficits. "Children are very vulnerable to the effects of mercury," Frery says. "We have observed that some of the children have difficulty in coordination and appear to have other subtle neurological problems."

Frery and coauthor Alain Boudou are returning to French Guiana this year to determine the severity and importance of the neurologic effects noted, and to see if programs can be established to decrease mercury ingestion by the Wayanas, even in the face of continued gold mining operations. Jointly to these studies on Wayana communities, a multidisciplinary program is being conducted in French Guiana to investigate the chemical fate of mercury in air, soil, and fresh water and to analyze the transfer process along the food web.