Bioconcentration of chlorpyrifos by the three-spined stickleback under laboratory and field conditions

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One of the aims of using kinetic models in aquatic toxicology is the prediction of residue levels of contaminants in aquatic organisms. However, only few investigations have compared residue levels observed in field tests to levels predicted through the use of laboratory-derived kinetic parameters. This paper investigates the feasibility of predicting the concentration of the organophosphorus insecticide chlorpyrifos in fish in outdoor mesocosms, using uptake and elimination rate constants determined in the laboratory. To this end three-spined sticklebacks were exposed to the insecticide in the laboratory and in three outdoor ditches. The lipid-based bioconcentration factor of chlorpyrifos in the sticklebacks was found to be (21 ± 4)·10 3 1 kg −1 in the laboratory. Uptake and elimination were succesfully described using a first-order one-compartment kinetic model. The lipid-based uptake and elimination rate coefficients were (26 ± 8)·10 3 1 kg −1 d −1 and 1.2 ± 0.4 d −1 respectively. The chlorpyrifos concentrations observed in sticklebacks which were taken from the mesocosms during the field study were found to be higher than calculated using the laboratory-derived toxicokinetic parameters. Discrepancies between expected and observed residues were similar for the two low-exposure ponds. The ratio between observed and expected residues was significantly higher in the third (high-exposure) ditch. It is concluded that the application of first-order one-compartment models, using laboratory-derived uptake and elimination rate coefficients, for the prediction of residues of chlorpyrifos in sticklebacks should be limited to concentrations far below the compounds LC50. Using the model at relatively high aqueous concentrations is likely to result in a significant underestimation of the residues in fish tissue.