How Does Pollution Affect a Food Web?
The concentration of pollutants in a food web (a community of interdependent organisms) can become magnified in organisms at higher trophic levels. While the initial concentration of pollutants may not be high enough to cause harm, severe abnormalities may result as these pollutants become increasingly concentrated in higher trophic and longer-lived species.
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Pollutants Entering the Food Web
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Primary producers take up inorganic nutrients from the surrounding soil or water. These producers can also consume pollutants such as mercury, the insecticide DDT and PCB (polychlorinated biphenyl).
Concentration of Pollutants
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Even low levels of environmental pollutants can become concentrated in the primary producers as they store these pollutants in their cells and tissues.
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Grazers
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A small amount of pollutant in these primary producers becomes concentrated in grazers (organisms that feed on producers) due to the sheer volume of material consumed.
Predators
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Predators of these contaminated grazers further concentrate the pollutants in their own bodies.
Top Predators
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Top-level predators tend to have very high concentrations of the pollutants due to the concentration of already high levels of contaminant in their prey. This has led state health authorities to issue warnings to avoid eating top-level predators, sharks for example.
Effects of Biological Magnification
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A number of physiological disorders are associated with abnormally high levels of certain pollutants in top-level predators. These include reproductive problems, organ failure and nervous ailments. For example, high levels of PCB have been linked to sterility and liver failure in bears, whales and other top predators.
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