The utility of solid-phase microextraction in evaluating polycyclic aromatic hydrocarbon bioavailability during habitat restoration with dredged material at moderately contaminated sites.

The over- or underprediction of risk in moderately contaminated sediments can have a large impact on the nature of applied management strategies given that concentrations border on being toxic or not toxic. Project managers should give significant consideration as to how moderate levels of contaminants in native sediments and dredged material used for restoration will impact recovery of habitat. Total solid-phase (Ctotal ) and porewater (Cfree ) polycyclic aromatic hydrocarbons (PAHs) were quantified in native sediments and dredged material to determine if the predictions of risk from Ctotal are consistent with those based on Cfree . The sediment matrix phase in which PAHs were quantified resulted in disparate conclusions regarding the predicted reduction in contamination following restoration. Total solid-phase PAH concentrations suggested a significant decrease following restoration, whereas little to no change was observed in measured Cfree . Risk metrics based on Ctotal gave inconclusive estimates for toxicity, whereas measured Cfree suggested toxicity is unlikely, a conclusion consistent with toxicity testing. The incorporation of black carbon (BC) into model estimates for Cfree gave predictions more consistent with measured Cfree , suggesting that geochemical conditions (especially BC) play an important part in predicting toxicity at moderately contaminated sites. In addition to the use of Cfree in toxicity evaluation, in-situ Cfree measurements provided a constraint on diffusive PAH loads from sediment relative to ongoing stream loads. If passive sampling had been employed during the sampling designs and site evaluations, the costs of toxicity testing would not have been incurred, given that Cfree suggested little to no toxicity. The results from the project highlight the benefits to be gained by moving beyond inconclusive, screening-level Ctotal metrics and implementing more sensitive and accurate Cfree metrics in assessments of risk in moderately contaminated sediments. Integr Environ Assess Manag 2018;14:212-223. © 2017 SETAC.