Ecotoxicology is a relatively new science concerned with contaminants in the biosphere and their effects on constituents of the biosphere, including humans. Although relevant effects range from the molecular to the biospheric levels of biological organization, most measures of effect generated by ecotoxicologists are designed to infer adverse effect at the level of the individual organism. This is a consequence of core methods adoption from classic toxicology, a discipline appropriately concerned with effects on individuals. This has created a bias in the ecotoxicology literature that can compromise inferences about effects at higher levels of biological organization such as the population, ecological community, or ecosystem levels. Despite this bias, the methods described herein can and are used pragmatically to infer effects including those occurring at higher levels.

Effect metrics are derived for different kinds of exposures, most notably acute exposures to high concentrations and chronic exposures to low concentrations. Acute exposures are defined in various ways but all definitions reflect a relatively brief and intense exposure scenario. By recent convention, chronic exposures are defined as those exceeding 10% of an individual's life span. However, the definition of chronic exposure varies in literature and depends on the specific methodologies used to produce an effect metric. As an example, some chronic toxicity tests for aquatic species use an exposure duration of 28 days regardless of the longevity of the test species.

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