A passive sampler based on solid-phase microextraction for quantifying hydrophobic organic contaminants in sediment pore water.

Sediment-quality assessment often is hindered by the lack of agreement between chemical and biological lines of evidence. One limitation is that the bulk sediment toxicant concentration, the most widely used chemical parameter, does not always represent the bioavailable concentration, particularly for hydrophobic organic compounds (HOCs) in highly contaminated sediments. In the present study, we developed and tested a pore-water sampler that uses solid-phase microextraction (SPME) to measure freely dissolved (bioavailable) HOC concentrations. A single polydimethylsiloxane (PDMS)-coated SPME fiber is secured in a compact, protective housing that allows aqueous exchange with whole sediment while eliminating direct contact with sediment particles. Fibers with three PDMS coating thicknesses were first calibrated for 12 model HOCs of current regulatory concern. Precalibrated samplers were exposed to spiked estuarine sediment in laboratory microcosms to determine the time to equilibrium and the equilibrium concentrations across a range of sediment contamination. Time to equilibrium ranged from 14 to 110 d, with 30 d being sufficient for more than half the target HOCs. Equilibrium SPME measurements, ranging from 0.009 to 2,400 ng/L, were highly correlated with but, in general, lower than HOC pore-water concentrations determined independently by liquid-liquid extraction. This concept shows promise for directly measuring the freely dissolved concentration of HOCs in sediment pore water, a previously difficult-to-measure parameter that will improve our ability to assess the impacts of contaminated sediments.