Using polyethylene passive sampling to assess transport of polychlorinated biphenyls (PCBs) between contaminated sediments, water, and biota

Abstract

Polychlorinated biphenyls (PCBs), which were a widely used group of chemicals before their manufacture was banned in 1979 in the United States, still contaminate numerous aquatic systems. Although there are ongoing efforts to remediate these sites, our ability to implement effective remediation strategies has been hindered by a limited understanding of how PCBs are transported in the environment as well as how they bioaccumulate into aquatic animals. Investigations of contaminated sites often rely on sediment measurements since PCB concentrations are highest in the sediment phase. However, previous research has shown that sediment concentrations are a poor predictor of contaminant fate and effects, whereas freely dissolved water concentrations were able to predict the extent of bioaccumulation and the onset of toxicological effects more accurately.

Additionally, the concentration gradient between the porewater (i.e., the interstitial water in sediment beds) and the overlying water is thought to be a major driver in PCB transport from the sediment bed. Passive samplers, which are made of polymers like polyethylene (PE), accumulate PCBs when they are deployed into environmental media, can be used to estimate freely dissolved water concentrations. When used in the laboratory by mixing with sediment samples, they provide a measure of the sediment-water equilibrium porewater concentration. When deployed in the field, they can provide measures of the in situ porewater and overlying water concentrations. In this work, PE samplers were deployed at two Superfund sites contaminated with PCBs to investigate if in situ porewater and sediments were at equilibrium with each other.

In situ porewater concentrations were consistently found to be lower than equilibrium concentrations at both sites, an effect that was likely caused by water flow through the sediment bed. At one of the sites, measurements of a geochemical tracer also showed that the exchange of porewater with overlying water was occurring and that the transport of PCBs from sediments was affected by more than just the concentration gradient. Lastly, the sorptive disequilibria between environmental media and the spatial heterogeneity of contamination were shown to affect the extent of bioaccumulation in aquatic animals at one of the sites.