Fisheries and Oceans Canada research scientist Paul Blanchfield and his team used one of the lakes at northwestern Ontario’s International Institute for Sustainable Development-Experimental Lakes Area (IISD-ELA) to conduct the study.
The controlled environment at IISD-ELA allowed the team to add special forms of mercury into the lake and its watershed over seven years. As expected, mercury levels in the lake and methylmercury in fish increased.
Surprisingly, methylmercury levels decreased by 76% in northern pike and 38% in whitefish, eight years after they stopped adding mercury to the lake.
This is significant as mercury is one of the most widespread contaminants in the province, resulting in fish consumption advisories on many waterbodies. While mercury is naturally occurring, human activity, such as burning coal, has increased its levels. Mercury emitted to the atmosphere can be transported long distances before falling in rain. Some mercury that ends up in lakes is converted to methylmercury by bacteria. Methylmercury accumulates in the food chain, and tends to be highest in top predatory fish, like pike, walleye, and lake trout. Exposure to too much methylmercury can be harmful to humans.
Situation gradually improving
“The situation has generally been improving due to efforts to reduce atmospheric mercury emissions,” Blanchfield said. “However, changes in food web structure through the introduction of invasive species, for example, and climate change can alter mercury accumulation by fish. In addition, large stores of mercury already in lakes and their watersheds from centuries of mercury pollution made it difficult to understand the effectiveness of pollution control measures from standard monitoring data alone. This is one of the reasons why we needed to undertake this whole ecosystem experiment.”
Blanchfield is hoping his findings will influence policy change. “We hope that the findings from our study will make it clear to policy makers that reducing mercury emissions to the environment is beneficial to fish consumers,” he said.