Equilibrium Porewater Measurement of PCBs and PAHs Using Direct Water Extraction and Comparison with Passive Sampling

The freely dissolved concentration of hydrophobic pollutants in sediment porewater (C_pw) is a critical driver for exposure to aquatic organisms, bioaccumulation, toxicity, and flux across interfaces. In this research, we compared direct porewater extraction and passive sampling for C_pw measurements of a range of PCBs and PAHs in field-collected sediments. The direct water extraction method provided accurate quantification of C_pw for low to moderately hydrophobic PCB and PAH compounds (log K_ow < 6.5) that compared well with independent measurements performed using four passive sampling methods. Direct water extraction was adequate to assess narcosis toxicity of PAHs to benthic organisms that is driven by the concentrations of low to moderately hydrophobic PAHs (naphthalene to chrysene), even for a hypothetical sediment that had a tenth of the PAH concentrations of the study sediments and was assessed to be nontoxic. Prediction of PCB bioaccumulation in benthic organisms agreed within 50% for all measurement methods, but it was apparent that for less contaminated sediments, the direct water extraction method would likely have detection limit challenges, especially for the strongly hydrophobic PCBs. To address the uncertainty of the C_pw measurement of the strongly hydrophobic compounds and naphthalene, a new extrapolation approach is demonstrated that can be applicable for both direct water extraction and passive sampling methods.