EPA's Report on the Environment: External Review Draft
Ecological Exposure to Contaminants
Ecological Exposure to ContaminantsWhat are the trends in biomarkers of exposure to common environmental contaminants in plants and animals?
Importance of Ecological Exposure to Contaminants
Environmental contaminants, such as chemicals introduced into the environment intentionally (as with fertilizers, pesticides, and herbicides) or unintentionally (through accidental spills or leaks of chemicals used in home and commercial applications), can harm plant and animal communities. At sufficient exposure levels, environmental contaminants can begin to have toxic effects on individuals within animal or plant populations. When a sufficient number of individuals are affected, contaminant exposure can change the structure and functioning of ecological systems.
Biomarkers of Contaminant Exposure
Ecological exposure to contaminants is tracked using biomarkers of contaminant exposure. Biomarkers measure either the levels of a contaminant (or its byproducts) in plant or animal tissue or the organism's biological response to the contaminant. Examples include:
- Tissue levels of pesticides, PCBs, and mercury, which have been used for many years to evaluate exposures in the brown pelican, bald eagle, lake trout, and a host of other fish and wildlife species.
- Pathological anomalies in plant or animal tissue, such as bleaching of plant tissue from ground-level ozone.
- Tumors in fish exposed to sediment contaminated with polycyclic aromatic hydrocarbons (PAHs).
- Biomarkers can be used to gauge the health of plant and animal communities over time.
- When coupled with other information (such as toxicity testing results), biomarkers of contaminant exposure can provide a basis for estimating the levels of a chemical stressor that plant and animal communities can and cannot tolerate.
- Decreases in biomarker levels can also help explain the recovery of certain animal populations, such as the brown pelican, that were once nearly driven to extinction by specific chemical stressors.
- Biomarkers can provide an indication of exposure levels throughout food webs. For example, the Mussel Watch program relies on sampling mussels and clams for many chemicals to evaluate exposures in coastal areas. Mussels and clams filter water to obtain their food, which exposes them to chemicals in the water.
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Three national-scale ROE indicators are available to address this question: Coastal Fish Tissue, Lake Fish Tissue, and Ozone Injury to Forest Plants. Indicators for tracking exposure are limited due to several challenges, including the limited number of biomonitoring programs and the challenge of determining whether the function of plant or animal communities is being affected by the exposure being monitored.