PT18 Population-Level Ecological Risk Assessment
Exhibit Hall
8:00 AM - Tuesday
(PT272) Individuals versus Organisms versus Populations in the definition of Ecological Assessment Endpoints.
Suter, G1, Fairbrother, A2, Munns, W3, Norton, S4, Wentsel, R4, Kravitz, M1, 1 Office of Research and Development, U.S. EPA, Cincinnati, OH, USA2 Office of Research and Development, U.S. EPA, Corvallis, OR, USA3 Office of Research and Development, U.S. EPA, Narragansett, RI, USA4 Office of Research and Development, U.S. EPA, Washington, DC, USA
ABSTRACT- The issue of defining ecological assessment endpoints at the organism and population levels of organization has caused confusion and acrimony, despite recent documents that attempted to elucidate the issue. Semantic confusion surrounding the terms individual, organism, and population in risk assessment may be clarified by comparing their use in human health and ecological risk assessments. Risks at the organism level may be described in terms of individual organisms (e.g., probability of death) or in terms of the organisms in a population (e.g., the frequency of death or death rate). Both of these types of endpoints are used in human health risk assessment, but the risks to a reasonable maximally exposed individual are emphasized. In ecological assessments, individual risks are estimated only for endangered species or similarly valued species. The most common ecological assessment endpoints are attributes of organisms in a population or community such as survival, growth, reproduction, which may be expressed as averages, rates, or frequencies. Population endpoints in ecological assessments include true attributes of the population level of organization such as extinction, production, and abundance. These ecological population endpoints are not used in human health risk assessments, because effects on human population attributes are not countenanced. Protection of attributes of organisms, such as survival, has been indicated by laws and regulations and has been upheld by the U.S. Federal Courts. It has practical advantages in that toxicity tests directly report relevant values, and protection of the attributes of organisms within a population may be assumed to provide some degree of protection of population attributes. However, there are cases in which population attributes are the appropriate endpoints for an ecological risk assessment. The levels of protection provided by a management decision depend on the choice among these types of endpoints.
Key words: population, endpoint, organism, ecological risk assessment