Abstract. An assessment was made of the in situ bioaccumulation of 13 polycyclic aromatic hydrocarbons (PAHs) in freshwater isopods in relation to their partitioning between sediments, particulate matter (Ͼ0.7 µm), and dissolved phases in eight different water systems of The Netherlands. Large differences in total (⌫ PAHs) concentrations and in relative abundance of individual PAHs were observed between organisms and abiotic compartments and among sampling stations. Principal component analysis revealed distinct differences between PAH profiles in sediments and water. High molecular weight PAHs dominated in the sediments, fluoranthene and pyrene in the isopods, and naphthalene in water. Apparent lipid-based bioconcentration factors (BCFs) increased with increasing hydrophobicity (n-octanol/water partition coefficient; K ow ). The total range of the BCFs varied only one order of magnitude, ranging from 10 5

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 techniques 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 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 slowly (t 0.5 : 99to>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 K ow (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 K ow. 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.