One of the benefits of passive sampling with polymer-film strips is that the same material can be used to sample water in a well-mixed water column and porewater in an unmixed porous media. This feature was exploited to determine the flux of contaminants due to molecular diffusion across the sediment-water interface at a site that posed technical challenges using more traditional techniques for sampling water and porewater. The Palos Verdes Shelf (PVS) Superfund site is in over 50 meters of water on the continental shelf and slope off the coast of southern California (USA). The site includes more than 25 km2 of sediments contaminated over several decades by municipal treatment plant effluent discharged via off-shore outfall pipes. Contaminants of concern include polychlorinated biphenyls (PCBs) and the pesticide DDT and its degradation products (e.g., DDE). In this study, strips of polymeric passive samplers (polyethylene (PE) and polyoxymethylene (POM)) were deployed across the sediment-water interface at four stations within the Palos Verdes Shelf Superfund site, including one station within a pilot remedial sand cap. In addition, samplers were deployed at one station (Santa Monica Bay) far from the Superfund site. The deployment platforms were designed to allow sampling of the sediment interstitial waters at 2 cm increments to a depth of up to 20 cm, and to sample the bottom water in the 20 cm above the sediment-water interface. Dissolved concentrations determined using both types of samplers agreed within an order of magnitude for the nineteen contaminants measured (five DDT breakdown products and fourteen PCBs), but differences were observed in the reproducibility of results and in the transfer of performance reference compounds and target compounds between polymer and sediments beds or water column. Within the Superfund site, diffusive fluxes at stations outside of the pilot remedial sand cap area were similar to those measured at a station inside the capped area: 240 to 260 ng cm-2 y-1 for p,p’-DDE. Flux was not detectable at the Santa Monica Bay station because concentrations in the water column and sediment porewater were too similar. This work demonstrates the utility of passive samplers for making in situ flux measurements at contaminated sediment sites, which will guide decisions on which stations receive priority for environmental remediation.

Calculating the diffusive flux of DDTs and PCBs across the sediment-water interface at the Palos Verdes Shelf Superfund site using polyethylene and polyoxymethylene passive samplers

250th National Meeting (2015)

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