KEY FINDING 11. Concentrations of legacy contaminants in terrestrial, freshwater, and marine systems have generally declined over the past 10 to 40 years. Concentrations of many emerging contaminants are increasing in wildlife; mercury is increasing in some wildlife in some areas.
This key finding is divided into five sections:
- Key finding overview (this page)
- Contaminant trends
- Trends in contaminants in the Great Lakes
- Interactions between contaminants and envrionmental change
- Effects of contaminants on wildlife
Contaminants are substances that are introduced into the environment through human activity. Some, like mercury, are naturally occurring but are increased in concentration through human activity to levels that could harm ecosystems and humans. Contaminants may travel great distances through the atmosphere and oceans and end up in ecosystems distant from their sources. This key finding considers only contaminants that persist in the environment and accumulate in the tissues of plants and animals. Legacy contaminants have been banned or restricted but are still widespread in the environment. Emerging contaminants are newer chemicals, or substances that have been in use for some time and have recently been detected in the environment – usually emerging contaminants are still in use or only partially regulated.
Contaminants can harm species and ecosystems and impair ecosystem services. They can directly affect animals when present in their diets, such as by impairing reproduction, and can also become a problem for humans who rely on them for food – particularly for Aboriginal people with diets heavily reliant on marine mammals and fish.1 The widespread presence of contaminants in wildlife has been a concern in Canada since the 1970s and concentrations of selected contaminants have been monitored in some species and locations over various periods since then. There are long-term, ongoing datasets adequate for trend analysis, but these are restricted to a few areas, such as the Great Lakes and parts of the Arctic.
Several persistent organic pollutants, including the pesticide DDT and the industrial chemicals PCBs, are considered legacy contaminants. Despite being banned or restricted, some of these substances persist at levels that may impair animal health in some populations of long-lived top predators (including killer whales2 and polar bears3) and in areas where there is a history of heavy use of some of these substances (such as the Great Lakes4).
Brominated flame retardants, for example PBDEs, are one class of emerging contaminants that have been detected in the environment, even in remote locations, at increasing levels since the mid-1980s. Concentrations of some brominated flame retardants show signs of stabilizing or declining in the last few years in response to new regulation and reductions in their use.1 Other emerging contaminants include some pesticides and herbicides in current use.
Mercury is a third example of a contaminant that can accumulate in wildlife. While mercury is a naturally occurring element, much of the mercury in marine and freshwater systems is from industrial sources such as coal burning – and mercury releases are increasing in parts of the world.5 Mercury levels in animals are highly variable and trends are mixed.1
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