Ecological Risk Assessment

Introduction ………………………………………………………………………………………………………………………….. 757 The Evolution of Environmental Toxicology and Ecological Risk Assessment ……………………………. 758 Ecological Risk Assessment: Definitions and Concepts…………………………………………………………….. 760 Risk Assessment Paradigm ……………………………………………………………………………………………. 760 Hazard Identification and Problem Formulation………………………………………………………. 760 Exposure Assessment or Exposure Characterization………………………………………………… 762 Exposure-Response Assessment or Effects Characterization ……………………………………. 762 Risk Characterization……………………………………………………………………………………………. 763 Risk Management …………………………………………………………………………………………………………………. 764 Comparison of Human Health and Ecological Risk Assessment………………………………………………… 765 Hazard Identification or Problem Formulation…………………………………………………………………. 766 Assessment Endpoints…………………………………………………………………………………………………… 766 Extrapolation and Testing ……………………………………………………………………………………………… 766 Integration of Human Health and Ecological Risk Assessment………………………………………………….. 767 Applications of Risk Assessment ……………………………………………………………………………………………. 767 Uncertainty in Risk Assessment ……………………………………………………………………………………………… 768 Challenges for Toxicology to Advance Ecological Risk Assessment ………………………………………….. 771 Describing Ranges of Effect Rather Than Single Thresholds ……………………………………………. 771 Interpreting Sublethal Effects ………………………………………………………………………………………… 771 Identifying Modes of Action Not Represented by Standard Assays …………………………………… 772 Better Extrapolation/Reducing Animal Usage………………………………………………………………….. 772 Multiple Stressors/Nonchemical Stressors……………………………………………………………………….. 772 Linkage of Organismal and Suborganismal Responses to Population and Community Response ……………………………………………………………………. 772 Conclusion……………………………………………………………………………………………………………………………. 773 Acknowledgments…………………………………………………………………………………………………………………. 773 References ……………………………………………………………………………………………………………………………. 773 Ecological risk assessment has been defined as “a process that evaluates the likelihood that adverse ecological effects may occur or are occurring as a result of exposure to one or more stressors” (USEPA, 1992). Conceptually, risk assessment is implied by Paracelsus’ observation that “only dose differentiates a remedy from a poison.” Risk is not an inherent property of a chemical toxicant but rather the product of its toxicity and the exposure received. Hence, the same chemical can show little risk at low exposures, but high risk at high exposures. This basic concept is embedded in our everyday behaviors. Gasoline is potentially very toxic to human beings, but we handle it without a thought on an almost daily basis. Why? Because even though gasoline has high toxicity, we have decided, consciously or unconsciously, that there is little chance that we would be exposed to that gasoline in a way and quantity that would cause us serious harm. It is this weighing of exposure and potential effect that is, in essence, a form of risk assessment.