A dynamic model for predicting chemical concentrations in water and biota during the planning phase of aquatic ecotoxicological tests

An unsteady-state fugacity model has been developed and validated as a predictive tool that will be useful in the planning phase of aquatic ecotoxicological tests. The model predicts the compound concentration trends in water and biota in experimental aquaria, with respect to the chemical and experimental conditions. The model has been validated with two echinoderm species, Paracentrotus lividus and Antedon mediterranea after a 28-days exposure to p,p'-DDE or triphenyltin chloride (TPT-CI), respectively. Differences between the predicted vs. measured concentrations of these compounds in water and biota were generally below a factor of two for both compounds. The model here proposed considers three different compartments, water, animals, and glass, and five loss processes: volatilisation, glass adsorption, abiotic degradation, bioconcentration and biotransformation. In particular, adsorption onto glass materials was introduced into the model by means of two equations (R-2 values of 0.86 and 0.90) relating the adsorption rate constant and glass-water partition coefficient on the base of the physical-chemical properties of the compound (log K-ow). The model can be applied during the planning phase of ecotoxicological tests and for understanding the behaviour of the compound at this micro-ecosystem scale after the tests have been performed.