Toxicokinetics and bioconcentration of polycyclic aromatic hydrocarbons in freshwater isopods

A novel method based on a first-order two-compartment model was used to determine the bioconcentration and toxicokinetic rate constants of six different polycyclic aromatic hydrocarbons (PAHs) in the freshwater isopod Asellus aquaticus, a common species in most European freshwater systems. Numerical integration and iterative parameter estimation technique- s were applied to account for time-varying aqueous exposure concentrations. All PAHs exhibited a rapid uptake. Monophasic elimination patterns were observed for benzo[e]pyrene and benzo[a]-pyrene (biological half-life t0.5: 7-8 days). For the other PAHs (anthracene, phenanthrene, pyrene, benzo[ghi]perylene) typical biphasic patterns were encountered with rapidly (t0.5: 0.6-2 days) and slowly (t0.5: 99 to > 1000 days) exchanging compartments. Some PAHs (pyrene and benzo[ghi]perylene) will hardly be eliminated during the normal life span of the organism. Bioconcentration factors (log BCF, wet weight; derived from rate constants) increased with molecular weight and Kow (n-octanol/water partition coefficient) from 2.6 L kg-1 (anthracene) to 5.7 L kg-1 (benzo[ghi]perylene). A linear relationship was observed between log BCF and log Kow. It is argued that biotransformation of PAHs in freshwater isopods seems to play a minor role and that this species may be suitable for the assessment of the bioavailability of PAHs in littoral freshwater environments.