Introduction

Managers and decision makers are challenged to solve complex environmental problems associated with the increasing pressures placed on vital natural resources by human activities. These challenges are made difficult by the sheer number and diversity of human disturbances and exacerbated by the complexity of imperfectly understood natural ecological systems. The process of ecological risk assessment (ERA) addresses ecological complexity and incorporates uncertainty in characterizing the impacts of natural and man-made disturbances on ecological resources.

ERA integrates ecology, environmental chemistry, environmental toxicology, geochemistry, hydrology, and other fundamental sciences in estimating the probabilities of undesired ecological impacts. In theory, ERA can be viewed as a subset of basic disturbance ecology. In practice, ERAs derive from specific needs to assess human-induced impacts on the environment. Many ERAs conducted in the United States are motivated by legislation, including the National Environmental Policy Act (NEPA), the Toxic Substances Control Act (TSCA), and the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA or Superfund). ERAs are also undertaken by private industry to determine future risks and liabilities associated with the development, use, and disposal (i.e., life cycle) of new or existing products (e.g., herbicides, pesticides, and industrial chemicals).

Several different approaches for performing an ERA have been developed internationally. No single methodology has been officially sanctioned. However, the approach developed by the United States Environmental Protection Agency (US EPA) guides many ERAs performed in the United States. The following discussion emphasizes this methodology.

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