Efforts to curb pollution in the Toronto waterfront over the past four decades have shown positive results in the health of sport fishes.
The latest study from the Ontario Ministry of the Environment and Climate Change and the University of Toronto analyzed government data on mercury, dioxin/furans and polychlorinated biphenyl (PCB) in local and migratory fish populations from 1975 to 2011.
What they found was not surprising, per se, but it did confirm that efforts to curb pollution in the Toronto waterfront over the past four decades have shown positive results in the health of sport fishes, said Satyendra Bhavsar, a research scientist with the ministry and the universities of Toronto and Windsor.
Mercury levels in seven sport fishes show an overall reduction between 46 per cent and 76 per cent among all fish examined.
Their study, published in the March edition of the Journal of Great Lakes Research, demonstrated that mercury levels in seven sport fishes – brown bullhead, brown trout, northern pike, rainbow smelt, white sucker, yellow perch and common carp – show an overall reduction between 46 per cent and 76 per cent among all fish examined. The trend suggests that mercury is no longer a serious contamination of concern for fish varieties in the Toronto area, Bhavsar told A\J.
Overall, PCB concentrations in northern pike, white sucker and brown trout have decreased by 76 per cent to 95 per cent while the other species saw little change. These reductions are significant, but the volume of PCB present in the water and its persistent nature means the decline is less substantial than it may appear. Releasing PCB into the environment has been illegal since 1985, but it accumulates easily in the fatty tissue of fish.
PCB has a half-life in fish from eight to 26 years, meaning fish today still suffer health effects from previous decades of PCB pollution. Contaminated fish can still pass those chemicals onto humans who eat them. Prolonged human exposure to polychlorinated biphenyl can stunt the neurological development of children, harm the reproductive system, alter thyroid hormone levels and compromise our immune system. It’s also a known carcinogen.
As such, despite a decline in contaminant levels, the concentration of PCBs in Toronto waterfront fish remains above the current advisory benchmark for safe consumption.
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But the slowdown in PCB reduction level is natural once major sources of pollution have been identified and controlled, Bhavsar said. It’s more important to remember the level of PCBs in the Toronto waterfront area is continuing a downward trend.
Contamination levels for mercury and PCBs have been declining since the 1972 implementation of the Great Lakes Water Quality Agreement, assisted by efforts to reduce stormwater flow into the watershed and improving spill-control efforts.
Urbanization has challenged remediation efforts along the 42 kilometres of Toronto waterfront.
While governments, industry and the general public have become more aware of the need to protect watersheds from terrestrial pollution, urbanization has challenged remediation efforts along the 42 kilometres of Toronto waterfront. The four million people who live on 2,000 square kilometres of land between the Rouge River in Scarborough and Etobicoke Creek in the city’s west end continue to impact the health of local fish populations.
Meanwhile, the vitality of Toronto’s sport fish stacks up well against other tested locations on the Great Lakes with regards to mercury. Mean mercury concentrations in the Toronto area were lower than those of a majority of tested locations in the Great Lakes, especially for northern pike and yellow perch. The Toronto area fared worse, however, when PCB levels were compared against other Great Lakes locales for all fish species.
But the study was about trends over time, Bhavsar said. And the bigger picture is upbeat.
“Fish contamination levels have declined dramatically,” he said. “The good part is that it is still ongoing, the levels are still declining and we should expect better levels in future.”
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