Microcosms as potential screening tools for evaluating transport and effects of toxic substances

Terrestrial and aquatic microcosms were evaluated for use in research on environmental contaminants. Research completed in this project attempted to: (1) evaluate relationships among size, complexity, stability, and replicability; (2) assess the simularity between microcosm results and actual environmental transport and effects; (3) identify and quantify system-level parameters that might be sensitive indicators of effects of chemical contaminants; (4) determine the relationship between system-level parameters measured in microcosms and in natural ecosystems; and (5) suggest protocols for establishing, maintaining, and interpreting results from microcosms. A number of experimental approaches using several microcosm designs and contaminants are reported. The use of terrestrial microcosm results was evaluated in conjunction with mathematical simulation models as a means of extending short-term exprimental results to interpret conditions as they might occur in the natural ecosystem. Although microcosms offer an excellent experimental system, their application to toxic substance testing is not a straightforward matter. They are characterized by complex dynamics and counterintuitive responses just as is the ecosystem to which they are an analog. These factors notwithstanding, microcosms do offer an excellent means of studying specific aspects of contaminant behavior and ecosystem processes. With appropriate attention to the design of specific questions, answers to which are relevant to interpreting ecological transport and effects of contaminants, microcosms can be useful tools.