• pond surrounded by green brush, reflecting a distant range of snow-covered mountains that are dominated by one massive mountain


    National Park & Preserve Alaska

Persistent Organic Pollutants (POPs)

Although Denali’s ecosystems are as intact as any in North America, and the scenery is breathtaking, these protected lands and waters are not as pristine as they may seem. Toxic airborne contaminants are accumulating in the arctic regions of the world, and Denali is no exception. DDT, the toxic chemical Rachel Carson warned about in her classic book, Silent Spring, is present in the sediments of Wonder Lake in concentrations among the highest measured in remote arctic lakes and rivers. DDT is one of many compounds classified as Persistent Organic Pollutants, or POPs, that are toxic to animals, including humans, and break down very slowly in the environment.

POPs can cause cancer, organ failure, and endocrine disruption, and other health effects, though it may take years of exposure for symptoms to be expressed. In the body, they are stored in fatty tissues, accumulating throughout an individual’s lifetime, and can become more concentrated at the upper levels of food chains through a process called bioaccumulation.

Arctic and subarctic ecosystems like Denali’s are particularly susceptible to accumulating POPs and other toxic airborne contaminants. In warmer climates, POPs are transported into an area, deposited from the atmosphere, and revolatilized back into the air. In colder parts of the world such as Denali, POPs are steadily deposited, but revolatilization is slower, so more contaminants remain in the ecosystem. Over time, this can lead to significant accumulation of POPs and other toxic airborne contaminants.

The National Park Service is embarking on a 5-year assessment program to determine the extent of POPs in Denali and six other national parks. You can find out more about this program, POPs, and other toxic airborne contaminants at the following web sites:

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