Duration of Elevated Mercury Levels in Fish in Boreal Reservoirs in Québec, Canada and Health Risk Management

At the La Grande hydroelectric complex located in northern Québec, Canada, the evolution of fish mercury levels was monitored from 1978 to 2012. Five fish species were followed: two non-piscivorous and three piscivorous. Total mercury concentrations (mg.kg^-1) were measured in more than 45,000 fish. In reservoirs, the average mercury concentrations in all species increased rapidly after impoundment, peaking after 4 to 11 years in non-piscivorous species, and after 9 to 14 years in piscivorous species, at levels 2 to 8 times higher than in surrounding natural lakes. Depending on the reservoir, the levels return to the same as found in fish in natural surrounding lakes after 10 to 20 years for non-piscivorous species and after 20 to 30 years in most piscivorous species.

To manage the potential health risks related to the marked but temporary increase in fish mercury levels, consumption guides were produced in collaboration with public health authorities and models to predict the duration and the level of the mercury increase in fish for future projects were developed. For non piscivorous species, the additional consumption restriction lasted for 0 to 26 years depending on the waterbody, while in piscivorous species it lasted for 0 to 30 years.