Mercury in Atlantic Canada: A Progress Report

Executive Summary

Over the past three years, in response to both international and regional concerns, Environment Canada Atlantic Region has lead a multi-disciplinary, interagency initiative to help determine the sources, fate and effects of mercury in the environment. Departmental scientists, along with many external research partners, have focused their studies on: determining the sources, fluxes and trends of mercury in air, water, vegetation and biota; identifying the environmental factors which influence the cycling of mercury in aquatic and terrestrial ecosystems and its uptake by plants and animals; and assessing the ecological impacts of observed mercury concentrations.

A great deal of progress has been made in our understanding of mercury in the environment of Atlantic Canada. Our results show that anthropogenic mercury emissions within the Atlantic provinces total about 960 kg/yr. Those regional emissions are about 6% of the Canadian total and about 6% of the total emitted in the northeast United States. Mercury concentrations in the air and precipitation in southwest New Brunswick and Nova Scotia are both similar to other sites in eastern North America. Both local and distant sources contribute to the mercury measured locally in air and precipitation. Historical patterns of atmospheric mercury deposition have been determined from bog and lake sediment cores taken within the region. Mercury deposition has increased 2 to 3 times since the onset of the industrial period in the mid-1800s. There are no obvious geographic gradients in mercury concentrations in lake waters within the region that can be related simply to long-range atmospheric transport. Total mercury concentrations in lake waters are influenced more by lake basin characteristics, such as the abundance of wetlands and aqueous concentrations of total organic carbon. In turn those same watershed factors, as well as lake acidity, appear to play a large role in influencing mercury levels in fish. Mercury concentrations were greater in larger, older predatory fish, especially those from acidic, brownwater lakes. Fish mercury concentrations varied widely among neighbouring lakes, when those lakes differed in lake chemistry. Mercury concentrations tended to be higher in freshwater fish than in comparable estuarine fish species. Mercury concentrations measured in the blood of common loons were very high in southwest Nova Scotia and high in southwest New Brunswick compared to the rest of North America. Mercury concentrations in both adult and juvenile loons were closely correlated with mercury concentrations in 10-cm yellow perch taken from the same lakes. A clear relationship was found between blood mercury concentrations in adult loons and their ability to nest and raise young. Current levels of mercury exposure appear to be impairing loon reproduction on acidic lakes in Nova Scotia and New Brunswick. Mercury also appears to adversely affect the behaviour of young loon chicks. Blood samples taken from juvenile osprey in Nova Scotia and New Brunswick had similar blood mercury concentrations to those observed in juvenile loons.

Despite those scientific advances, many important questions remain. The relative importance of natural vs. anthropogenic mercury sources to the air, lakes and biota studied remains unclear. Geographic patterns of mercury deposition and ambient concentrations in air, soils, lakes, fish and wildlife have not been determined extensively within the region, especially in Newfoundland and Labrador. It is presently unclear if the observed impairment of common loon reproduction will significantly impact regional loon populations over the long term. Similarly, impacts are unknown on regional populations of other fish-eating wildlife, like osprey, bald eagle, river otter and mink, which face similar mercury exposure.

With those and other questions remaining unanswered, it may prove difficult to predict the immediate benefits of regional control measures limiting mercury emissions to the environment. Nevertheless, there is growing evidence of environmental impacts associated with present levels of mercury in the environment of Atlantic Canada. Therefore any steps to prevent and reduce mercury pollution would be valuable.

Many of the potential control measures to deal with regional mercury use and emissions are under the jurisdiction of the provincial governments. The New England Governors/Eastern Canadian Premiers Mercury Action Plan, signed in Fredericton, NB in June 1998, outlines many recommendations to reduce mercury emissions, to promote source reduction and safe waste management, and to foster cooperative mercury research and monitoring. The following recommendations are made for future cooperative regional activities, in collaboration with provincial agencies and other partners, on the mercury issue: work in active partnership with provincial, state and federal counterparts in Canada and the United States, particularly in the areas of mercury research, assessment and strategic monitoring; maintain and enhance atmospheric monitoring of mercury in the region; further refine the regional mercury emissions inventory; expand the spatial data set of mercury concentrations in fish and use that information to conduct risk assessments on the impact of mercury on fish-eating wildlife; and develop an integrated ecosystem mercury model for use in predicting how mercury deposition in the Region will manifest itself in effects at the ecosystem level.