Interactions between the structural animo-polysaccharide, chitin, and the organophosphate pesticide, azinphosmethyl (Guthion), have been studied in a controlled continuous flow-through microcosm. Pesticide-induced microbial population changes and increases in substrate utilization of chitin are noted. Significant increases in total heterotrophs and chitinoclasts occurred relative to continuous application of azinphosmethyl. Rapid uptake and utilization of chitin and its derivatives, enhanced by controlled azinphosmethyl additions, were examined using a tagged chitin breakdown product, N-(glucosamine-1-14C)-acetyl-D-glucosamine. Rates of utilization coincided with rapid 14CO2 release, assimilation of 14C by microbial cells, and increases in colony forming units. Data correlations, using microbial and enzymatic criteria, inoculate the application of the benchtop microcosm in analyses of compound impact and substrate turnover.