Source: US EPA |
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Source: US EPA |
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| Introduction |
PCBs,
polychlorinated biphenyls, are colorless and odorless chemicals that were
widely used in electrical equipment and other industrial applications before
they were banned in 1976. These man-made chemicals are considered toxic
because exposure to small doses is suspected of contributing to a variety
of health problems. PCBs do not quickly decompose into less harmful chemicals,
so they are extremely persistent in the environment.
Of
the 1.4 billion pounds of PCBs produced in this country before 1976, about
half has entered the environment via discharges to air, land, and water.
Products that contain PCBs are also still being disposed of. The problem
is, PCBs remain mobile in the environment, leaching out of landfills into
rivers and lakes, and evaporating into the air. Scientific studies have
shown that atmospheric fallout accounts for a substantial amount of the
PCBs entering the Great Lakes today. Most PCBs in the environment end up in rivers, streams, lakes and, ultimately, the oceans. Once there, PCBs enter the food chain and become progressively concentrated from small organisms to large fish and, finally, in people who eat the fish. Many large, fatty fish like lake trout, carp, and chinook salmon have been found to contain PCB concentrations 100,000 to 1 million times greater than the concentrations in surrounding waters. As a result, some fish contain high enough PCB levels that they are considered unsafe for human consumption.
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| Purpose |
After
completing this investigation, students should be able to:
1.
Identify ways in which dangerous materials can enter the environment.
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From Decision
Making Activities for the Great Lakes, Toxins in Fish: How Should the
Public Health Be Protected?
Developed by the Ohio Sea Grant Education
Program, The Ohio State University. © 2003