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Report on the Environment

Ecological Exposure to Contaminants

What are the trends in biomarkers of exposure to common environmental contaminants in plants and animals?

Chemicals can be introduced to the environment intentionally (e.g., fertilizers, pesticides, and herbicides), or unintentionally through accidental spillage or leaks of chemicals used in home and commercial applications (e.g., in wastes from municipal and industrial operations). The extent to which the presence of mixtures of chemicals influences human health and the environment has long been a focus of EPA assessments.

Biomarkers of exposure can include measures of chemical concentrations in plant and animal tissue. Such measures provide insight into the magnitude of chemical exposure that organisms receive from their environment. Measures of biological response such as biochemical concentrations (e.g., enzymes and ligands) that respond to chemical exposures can also serve as biomarkers of exposure. Examples include histopathological anomalies such as plant tissue damage from ozone or tumors in fish exposed to sediment contaminated with polycyclic aromatic hydrocarbons (PAHs). This evaluation examines the trends in biomarkers of exposures to common environmental contaminants in plants and animals as presented in the ROE indicators. It also discusses challenges in assessing trends in these biomarkers.

Chemical stressors can have a detrimental effect on plant and animal communities. Exposure of plants and animals to chemical stressors can lead to increases in tissue concentrations of the chemical stressor in the plants and animals. Once stressor concentrations are above threshold levels, they can affect physiological systems within the plants and animals and can begin to have toxic effects on individuals within the population. These individual effects can lead to changes in plant and animal community structure when chemical stressor concentrations in the environment reach levels that can affect one or more species, or when the population numbers of a key species are detrimentally affected. Biomarkers of exposure, including concentrations of chemical stressors or key biomarkers collected over time within plant and animal tissues, can help to gauge the health of plant and animal communities over time. These biomarkers of chemical exposure, when coupled with other information (e.g., toxicity testing results), can provide a basis for estimating what levels of a chemical stress can and cannot be tolerated in the environment by plant and animal communities. These biomarkers also help explain the recovery of certain animal populations (e.g., brown pelican) that were once nearly driven to extinction by specific chemical stressors. Tissue levels of pesticides, PCBs, and mercury have been used for many years to evaluate exposures to such species as the brown pelican, bald eagle, and lake trout and a host of other fish and wildlife. The Mussel Watch program relies on sampling lower-trophic-level organisms (mussels and clams) for a broad range of chemicals to evaluate exposures in coastal areas. As these examples demonstrate, measures of bioaccumulative compounds in animal tissues provide an indication of exposure levels throughout food webs.

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