Polymer coated glass fibers were applied as disposable samplers to measure dissolved concentrations of persistent and bioaccumulative pollutants (PBPs) in sediment porewater. The method is called matrix solid-phase microextraction (matrix-SPME), because it utilizes the entire sediment matrix as a reservoir for an equilibrium extraction:  a glass fiber with a 15 μm coating of poly(dimethylsiloxane) (PDMS) was placed in a sediment sample until the PBPs reached their equilibrium distribution between the PDMS and the sediment matrix (1−30 days). PBP concentrations in the PDMS were determined by gas chromatography, and they were divided by PDMS water partition coefficients to derive at dissolved porewater concentrations. This approach was applied to measure porewater concentrations of spiked as well as field sediment, and several hydrophobic organic substances (log K OW 5.2−7.5) were measured with high precision in the pg to ng/L range. Simple equilibrium partitioning is the basis for the substantial concentration factors that are built into matrix-SPME and for the low demands in materials and operation time. Matrix-SPME was in this study directed at the determination of dissolved porewater concentrations in sediment, and it is further expected to be applicable to other environmental media, to field sampling, and to the sensing of fugacity.

There is an increasing body of evidence that the bioaccumulation of sediment-associated hydrophobic organic compounds (HOCs) is strongly influenced by sequestration. At present, it is not known how equilibrium partitioning theory (EqP), the most commonly employed approach for describing sediment bioaccumulation can be applied to sediments with sequestered contaminants. In this paper, we present freely dissolved pore-water concentrations of HOCs. These data were employed to interpret sediment bioaccumulation and sequestration data in order to arrive at a process based evaluation of EqP. The data analysis suggests that sediment bioaccumulation of compounds up to log K(ow) 7.5 in Tubificidae can be described as bioconcentration from pore-water. In addition, the pore-water concentrations of HOCs (4.5 < log K(ow) < 7.5) are established by equilibrium partitioning between the rapidly desorbing HOCs fraction in the sediment and the pore-water. Taken together, these findings indicate that EqP is a conceptually correct representation of sediment bioaccumulation, provided that sequestration is accounted for. This implies that the risk assessment of sediment-associated HOCs can be significantly simplified: With a method at hand for measuring freely dissolved pore-water concentrations of HOCs, it appears that HOCs' body residues in sediment dwelling organisms can be estimated on the basis of concentrations in pore-water and bioconcentration factors.

In the present study, the relationship between bioavailability of polycyclic aromatic hydrocarbons (PAHs) to benthic amphipods and the PAH desorption kinetics was examined. To that end, field-contaminated sediment was treated in three different ways. One subsample had no addition of PAHs and contained native PAHs only. To a second subsample, six PAHs (phenanthrene, fluoranthene, anthracene, pyrene, benzo[b]fluoranthene, and benzo[k]fluoranthene) were added in the laboratory. Two of the PAHs were added at higher concentrations to a third subsample, serving as a control for concentration-dependent uptake. Marine amphipods (Corophium volutator) were exposed to the three subsamples for a maximum of 25 d and were subsequently analyzed. Desorption kinetics were determined for both the lab-contaminated and the native PAHs. The biota-to-sediment accumulation factor (BSAF) values of the individual native and lab-contaminated PAHs correlated well with the rapidly desorbing fraction (R2 = 0.76). The BSAFs were 1.4 to 3.3 higher for the lab-contaminated PAHs compared with the native PAHs, while the difference between the rapidly desorbing fractions was a factor of 1.1 to 1.8. The BSAFs of the lab-contaminated PAHs in the second and third subsample were equal, indicating concentration-independent accumulation. The results suggest that lab-contaminated PAHs are more available to amphipods than native PAHs and that differences in bioavailability of lab-contaminated and native PAHs to marine amphipods are related to differences in desorption behavior.

In contrast to equilibrium partitioning model (EqP) calculations, biota to sediment accumulation factors (BSAF) of hydrophobic organic compounds for deposit-feeders are highly variable. Recent literature suggests that this variability can be attributed to differences in sequestration or the presence of slowly desorbing fractions in the sediment. In the present study, we investigated whether the observed relationship between bioavailability and sequestration is causal. We determined BSAF values and sequestration status, measured as the distribution over rapidly and slowly desorbing fractions, of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) in a manipulated sediment as well as in the original, unmanipulated sediment The manipulation, 48 h suspending with Tenax, resulted in reduction of the rapidly desorbing fraction, while other factors such as contact time and sediment properties remained constant. Contrary to expectations based on EqP, BSAF values did not remain constant but were reduced by a factor of 2-27, proportional to the reduction in rapidly desorbing fractions. The results provide direct evidence of a causal relationship between sequestration and bioavailability to deposit-feeders. Furthermore, the present study demonstrates the need to modify traditional use of the equilibrium partitioning model to account for variation in the sequestration status of HOC in sediments.

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