Polycyclic Aromatic Hydrocarbons in Freshwater Isopods and Field-Partitioning Between Abiotic Phases

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 (>0.7 µm), and dissolved phases in eight different water systems of The Netherlands. Large differences in total (Gamma 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; Kow). The total range of the BCFs varied only one order of magnitude, ranging from 10(5.1) (naphthalene) to 10(6.1) (benzo[a]pyrene). For PAHs with log Kow > 6.1 lower BCFs than expected were observed, which was attributed to reduced bioavailability, to the operational definition of the dissolved phase, and to growth dilution preventing equilibrium to be reached within the lifetime of the isopods. Abiotic partitioning coefficients, such as Koc (organic carbon normalized sediment-water partition coefficient) and Kpm (particulate matter-water distribution coefficient) increased with hydrophobicity for PAHs having a log Kow < 6.1. Sediment-water partition coefficients (Kd) increased with the organic carbon content of the sediments for most PAHs. It is concluded that isopods have a marked ability to accumulate PAHs and that their tissue residues tend to reflect spatial and temporal variations in the bioavailability of PAHs in littoral freshwater environments.