Toxicokinetics and bioconcentration of polycyclic aromatic hydrocarbons infreshwater isopods

A novel method based on a first-order two-compartment model was used to det ermine the bioconcentration and toxicokinetic rate constants of six differe nt polycyclic aromatic hydrocarbons (PAHs) in the freshwater isopod Asellus aquaticus, a common species in most European freshwater systems. Numerical integration and iterative parameter estimation techniques were applied to account for time-varying aqueous exposure concentrations. All PAHs exhibite d a rapid uptake. Monophasic elimination patterns were observed for benzo[e ]pyrene and benzo[a]pyrene (biological half-life t(0.5): 7-8 days). For the other PAHs (anthracene, phenanthrene, pyrene, benzo[ghi]perylene) typical biphasic patterns were encountered with rapidly (t(0.5): 0.6-2 days) and sl owly (t(0.5): 99 to >1000 days) exchanging compartments. Some PAHs (pyrene and benzo[ghi]perylene) will hardly be eliminated during the normal life sp an of the organism. Bioconcentration factors (log BCF, wet weight; derived from rate constants) increased with molecular weight and K-ow (n-octanol/wa ter 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 K-ow. It is argued that biotransformation of PAHs in freshwater isopod s seems to play a minor role and that this species may be suitable for the assessment of the bioavailability of PAHs in littoral freshwater environmen ts.