Field testing of equilibrium passive samplers to determine freely dissolved native polycyclic aromatic hydrocarbon concentrations

Equilibrium passive samplers are promising tools to determine freely dissolved aqueous concentrations (C-W,C-free) of hydrophobic organic compounds. Their use in the field, however, remains a challenge. In the present study on native polycyclic aromatic hydrocarbons (PAHs) in Oslo Harbor, Norway, two different passive sampler materials, polyoxymethylene (POM; thickness, 55 mu m [POM-55] and 500 mu m [POM-500]) and polydimethylsiloxane (PDMS; thickness, 200 mu m), were used to determine in the laboratory C-W,C-free in sediment pore water (C-PW,C-free), and the suitability of five passive samplers for determination of C-W,C-free in overlying surface water was tested under field conditions. For laboratory determinations of C-PW,C-free, both POM-55 and PDMS turned out to be suitable. In the field, the shortest equilibrium times (approximately one month) were observed for POM-55 and PDMS (thickness, 28 mu m) coatings on solid-phase microextraction fibers, with PDMS tubing as a good alternative. Low-density polyethylene (thickness, 100 mu m) and POM-500 did not reach equilibrium within 119 d in the field. Realistic values were obtained for dissolved organic carbon-water partition coefficients in the field (approximately one log unit under log K-OW), which strengthened the conclusion that equilibrium was established in field-exposed passive samplers. At all four stations, chemical activity ratios between pore water and overlying water were greater than one for all PAHs, indicating that the sediment was a PAH diffusion source and that sediment remediation may be an appropriate treatment for PAH contamination in Oslo Harbor.