Balancing human exposure, risk and reality: questions raised by the Canadian aboriginal methylmercury program.

Environmental contaminants such as methylmercury which bio-accumulate in aquatic ecosystems present an exposure risk to Aboriginal peoples living traditional lifestyles. The results of a 20 year testing program of methylmercury exposure levels of 38,571 Canadian Aboriginal people in 514 native communities across Canada are presented. 608 individuals had blood or blood equivalent levels over 100 micrograms/l. The highest individual level was 660 micrograms/l. The highest mean levels were found in the Inuit in N.W.T. In that same group, over 30% of women aged 15-45 years who were tested had levels over 10 micrograms/g methylmercury in hair with a mean of 16 micrograms/g, well into the 10-20 micrograms/g "risk" range defined by WHO for fetal exposure. A discussion of the management of risk from exposure to methylmercury in the Canadian Aboriginal population is presented, concentrating especially on the need to balance the theoretical basis of the risk assessment, for different population groups and for different exposure patterns, against the potential real impact on health caused by restrictive advice on consumption of traditional foods, especially fish.