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Backgrounder:
Toxic Metals Weigh Heavy on Birds
Mercury and lead are toxic metals released into the environment by natural and human activities. Although they are found in both terrestrial and aquatic habitats, they pose the most serious risk of poisoning to waterfowl, fish-eating birds and mammals, as well as the predators and scavengers that feed on these species.
Mercury is a major problem in aquatic habitats because certain environmental factors, including the acidity of the water and the presence of organic carbon, help to transform it into a form that is easily ingested by invertebrates and fish. The metal accumulates in the tissue of these organisms, and is biomagnified as it moves up the food chain.
Solid lead enters the food chain when lead shotgun pellets, or lead fishing sinkers or jigs are mistakenly ingested by birds. It also enters the chain when dead or wounded animals that contain lead shot are eaten by predators or scavengers. Lead has a relatively high toxicity, so adverse effects have been seen at even low levels of exposure.
Although the number of waterfowl killed in Canada each year as a result of ingesting lead shot has never been estimated, it was considered a potentially significant cause of mortality in game ducks before the ban was imposed. Birds of prey, such as eagles and owls, were also affected as a result of eating lead-contaminated prey.
Lead takes decades or even centuries to break down. It enters the environment through the hunting of big game, small game, and upland birds, and at target-practice ranges. Studies of lead levels in upland game birds, raptors and songbirds indicate that the frequency of high levels of exposure in these species is higher than was originally thought.
The ingestion of small lead sinkers and jigs by loons in lakes where sport fishing is popular also remains a problem. Lead poisoning accounts for up to 50 per cent of recorded adult loon mortality in Canada. It is also the leading cause of recorded deaths among adult Common Loons in North America during breeding season.
In 1997, Canada restricted the use of lead fishing sinkers and jigs in national wildlife areas and national parks. In Ontario, the province with the greatest angling pressures, Environment Canada has been involved in education and outreach programs to raise awareness of the impacts of lead on wildlife.
Fast Facts
- At least 50 per cent of mercury in the environment comes from fossil-fuel combustion, waste incineration and other industrial operations, such as smelting.
- Mercury levels in Herring gull eggs from sites across the Great Lakes are about half what they were in the late 1970s and early 1980s. This is due to a reduction in point-source pollution.
- Many lake bottoms contain up to 180,000 lead pellets per hectare, and some heavily hunted ones contain millions.
- Lead poisoning killed more than half of the Trumpeter swans which were released at Wye Marsh, Ontario, as part of a reintroduction program. Lead poisoning was also a common occurrence among swans wintering in southwestern British Columbia.
- A 1992 wingbone survey revealed that over 20 per cent of young-of-the-year Mallards and Black Ducks in Prince Edward Island, New Brunswick and Ontario had elevated lead levels.
- Twelve per cent of the Golden eagles and Bald eagles found dead in Saskatchewan, Alberta, Manitoba and British Columbia in the mid-1990s were found to be lead poisoned, and a further five per cent had elevated lead levels.
For more information on Fishing Lead-free please visit our website.
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