ABSTRACT
Adequate extrapolation of results from standard laboratory toxicity tests to other time scales of exposure and response requires observations on the time course of toxic effects. In the effect characterization of contaminants, both lower and higher tier toxicity tests may be performed for comparative, retrospective, or predictive purposes. Mathematical models have been developed and used to extrapolate toxicity under pulsed exposure conditions. Several compilations of vertebrate toxicity data have confirmed the consensus described for invertebrates that adult full-grown individuals are less sensitive to toxicants than are individuals at early life stages, although exceptions also exist. The arrangement and condition of individuals through time in a certain habitat are indicative of the local state of the population. Different populations of algae in the phytoplankton community were inhibited, stimulated, or apparently unaffected by atrazine. An advantage of field studies is that information can be obtained about recovery of disturbed populations and ecosystem functions.
