Methylation is accepted to be a major process controlling the biological availability of mercury, and a number of recent articles and reviews have addressed this process. Recently, the occurrence of elevated mercury in fish tissues from systems in regions considered to be remote from point or local sources of mercury have been documented.
These appear to be related to acidification of surface waters and to recent impoundments, usually in connection with hydroelectric dam construction. The present chapter addresses this second phenomenon, which is being investigated for Canadian Reservoirs by Environmental and Social Systems Analysts (ESSA) Ltd, LGL Associated and the University of Toronto in an ongoing study funded by the Canadian Electrical Association.
Elevated mercury levels have been detected in fish from a number of Canadian reservoirs. A preliminary study in 1976 of approximately 6000 fish throughout Labrador revealed that the highest mercury levels were found in fish from the Smallwood Reservoir and waters of the Churchill River downstream of the Control Structure. The maximum mercury levels in burbot (1.93 Jlwgm) and in lake trout (3.9 Jlwgm) were in fish from the reservoir.”