The process of bioconcentration considers (1) the uptake of chemicals directly from an organism's environment and (2) the depuration or loss of that chemical or its metabolites from the organism. For example, in fish a bioconcentration factor represents the ratio of concentration of chemical in fish tissues to concentration of chemical in the water, and the desire to predict the BCP for any chemical has stimulated the development of model systems investigating the metabolism and environmental fate of a number of chemical species. Here, the bioconcentration of a representative polynuclear aromatic hydrocarbon, anthracene, was considered in a series of experiments using rainbow trout in single compound and complex chemical mixture exposures.