Bioconcentration kinetics of chlorobenzenes and the organophosphorus pesticide chlorthion in the pond snail Lymnaea stagnalis - A comparison with the guppy Poecilia reticulata

Bioconcentration factors and uptake and elimination rate constants are determined for seven chlorobenzenes and for the organophosphorus pesticide chlorthion in the pond snail Lymnaea stagnalis. The toxicokinetic parameters are related to octanol-water partition coefficients (K(ow)) and compared with literature data for the guppy (Poecilia reticulata). In contrast to the guppy, uptake rate constants for chlorobenzenes in the pond snail increase proportionately with K(ow) in the pond snail. Elimination rate constants decrease with increasing K(ow) values, similarly to the guppy. Absolute elimination rate constants, however, are higher than in the guppy. For the pond snail, the relationship between bioconcentration factors of chlorobenzenes and hydrophobicity is described as: log BCF = 1.97 log K(ow) - 7.45 (r2= 0.93). The slope of this relationship is remarkably steeper than for the guppy and aquatic organisms in general. Bioconcentration kinetics of clorthion in the pond snail do not suggest a significant impact of biotransformation. By means of the application of the fish kinetic bioconcentration model, differences in the kinetic behaviour of chlorobenzenes in the guppy and the pond snail are examined with respect to differences in their weight, surface area and lipid content. The observed higher elimination rates in the pond snail are reasonably well predicted by the model and can as such be explained by its lower lipid content in combination with its slightly lower surface to mass ratio. Uptake rate constants of the lower chlorinated benzenes in the pond snail are substantially overestimated by the model. Furthermore, the model seems incompetent to describe their dependency on hydrophobicity. The insufficiencies of the model are discussed with respect to possibly inaccurate assumptions in parametrization of the model and to the model itself, being founded on first-order one-compartment kinetics and diffusive mass transfer. Protein binding is suggested to be most likely responsible for the observed discrepancies.