PAH bioavailability in field sediments: comparing different methods for predicting in situ bioaccumulation.

In situ exposure concentrations of chemicals in sediments and their depending risks are determined by site-specific parameters (e.g., sediment organic carbon composition), controlling bioavailability. Over the years, several analytical methods have been developed to assess bioavailable concentrations or fractions. Some of these methods have been successful in the laboratory, but few attempts have been made to test their potential for predicting actual in situ bioavailability. In this study, solid-phase microextraction (SPME)-fibers and aquatic worms (Lumbriculus variegatus) were exposed in situ at three locations. In addition, laboratory-based methods, i.e., methods with which sampling of the bioavailable fraction/concentration took place in the laboratory, being SPME, polyoxymethylene solid-phase extraction (POM-SPE), hydroxypropyl-beta-yclodextrin-(HPCD), and 6 h-Tenax extraction were applied to sediments collected at the locations. Using equilibrium partitioning-based calculations, biotic PAH levels were calculated from the concentrations or fractions extracted by the used methods. In general, method-predicted concentrations were within a factor of 10 of those measured in field-exposed oligochaetes, with in situ SPME and laboratory-based POM-SPE yielding the best results. As a reference, the currently used generic risk assessment approach overpredicted biotic concentrations by a factor of 10-100, which corresponded to in situ SPME-derived sediment-water distribution coefficients and biota-to-sediment accumulation factors being up to 2 orders of magnitude higher and lower, respectively, than generic values. These observations advocate site-specific risk assessment for PAHs, for which potential tools were evaluated in this study.