T4 AM Endangered Species and Environmental Contaminants: Status of the Science (Part 1)
Tuesday, 15 November 2005: 8:00 AM - 11:40 AM in Ballroom 4

(STA-1117-648013) Toxicity endpoints used in risk assessment: What do they really mean?

Stark, J¹, ¹ Washington State University, Puyallup, WA, USA

ABSTRACT- Acute lethal concentration estimates (LC50) are the most widely developed measure of toxicity and are often used in the ecological risk assessment process for the protection of threatened and endangered species. Uncertainty factors such as 1/20th of the LC50 are also used to compensate for a lack of knowledge of the impacts that pesticides and other toxicants might have on particular species. Exposure to toxicants can cause multiple sublethal effects. Therefore, the LC50 may be woefully inadequate as a measure of effect on populations. Recent studies have shown that LC50s cannot be compared among species to predict population-level outcomes because of differences in life history variables. For some species, 50% mortality will result in significant population declines, while for others, 50% mortality will only slow population growth slightly. In other words, 50% mortality or 50% reduction in fecundity does not mean the same thing for all species. In this presentation, measures of toxicity based on individuals will be compared to effects on actual populations. A modeling approach will also be used to show possible outcomes of lethal and sublethal effects on populations. The value of various endpoints of toxicity for prediction of population effect will be discussed.

Key words: ecological risk assessment, LC50, modeling, pesticides