A key element of any risk assessment is a clear and precise statement of risk. This is especially challenging in a probabilistic risk assessment, where statements about �likelihood� are meaningful only in the context of the assumptions � implicit and explicit � under which the risk estimates are made. Examples of probabilistic risk statements are drawn from the higher-tier ecological risk assessment of pyrethroid insecticides detailed in other posters and presentations in this symposium. Risk statements can be framed differently to address specific questions, such as, �What fraction of water bodies in a watershed, a region, or nationally are expected to exceed the threshold of ecological effects more than 1 year in 10?� or �What fraction of applications are expected to result in one or more water bodies exceeding the threshold of ecological effects?� In each case, the risk statements are accompanied by a full accounting of the assumptions of the exposure modeling, such as the dimensions of the water body, the watershed landscape, soil properties, climate, and application practices, as well as a clear definition of the threshold for ecological effects.

Probabilistic risk characterization statements: Examples from a higher-tier assessment of synthetic pyrethroids

248th National Meeting (2014)

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.