CONICET | Buscador de Institutos y Recursos Humanos

We have studied the distribution and bioelimination of the organophosphorus pesticide parathion in a native microcosm consisting of water, sediment, bivalves and aquatic plants. A common apparent clearance constant for biotic and abiotic components was suggested from the analysis of parathion accumulation and degradation.In this work we developed a global model explaining the toxicokinetics of a lipophilic compound and particularlarly the common steady state degradation in an aquatic microcosm, using a set of linear differential equations. We simulated the distribution and degradation of the compound in the microcosm, and fitted sigle-compartment equation models to data, estimating the apparent sorption and elimination constants. We verified the existence of a common apparent degradation constant for all the components. We infer from the mathematical expressions and corroborate from the simulated data that the apparent degradation constant is equal to the sum of the metabolic rates at each biotic compartment multiplied by the compound mass ratios established at steady state between the biotic and the abiotic compartments.Product kinetics simulation showed that steady state might also be achieved in the different compartments, with the same apparent constant as that obtained for toxicant clearance. As a practical result, the total radioactivity in water would serve to calculate the global clearance constant in a simple experimental way if a radiotracer is used. Physical and chemical degradation and chemical loss due to volatilization and CO2 diffusion were analyzed in the microcosm model. The assessments of the cases where these factors affect the clearance process as well as the implications emerged are discussed.

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