Fate analysis predictions of agricultural or industrial source toxicants in aquatic or marine environments can be affected by the presence or absence of adapted (preexposed) microbial populations and amenable substrates for cometabolic or cooxidative biotransformation. Polychlorinated biphenyls (PCBs) were evaluated in controlled laboratory microcosm systems in the presence of the aminopolysaccharide polymer chitin. Toxicants evaluated included the commercial Aroclors 1232, 1248, and 1254. Crosscouplings of each PCB mixture and polymer were noted, resulting in an optimization of epiphytic microbial metabolic activity. Significant primary degradation was noted for the lesser chlorinated biphenyls, that is, Aroclor 1232. Gas chromatography analysis of Aroclor 1248 and 1254 showed several tetra and penta isomers remaining. However, when polymer epiphytic populations were predominantly adapted microbial strains, that is, a Pseudomonas species and an Acinetobacter species, additional refractile isomers were metabolized. A comparison of kinetic rate constants based on biotransformation of each commercial mixture showed significant changes in halflife as correlated to isomer mixture, available polymer, and microbial inoculation.