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

Abstract

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 (C ) and porewater (C ) polycyclic aromatic hydrocarbons (PAHs) were quantified in native sediments and dredged material to determine if the predictions of risk from C are consistent with those based on C . 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 C . Risk metrics based on C gave inconclusive estimates for toxicity, whereas measured C suggested toxicity is unlikely, a conclusion consistent with toxicity testing. The incorporation of black carbon (BC) into model estimates for C gave predictions more consistent with measured C , suggesting that geochemical conditions (especially BC) play an important part in predicting toxicity at moderately contaminated sites. In addition to the use of C in toxicity evaluation, in-situ C 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 C suggested little to no toxicity. The results from the project highlight the benefits to be gained by moving beyond inconclusive, screening-level C metrics and implementing more sensitive and accurate C metrics in assessments of risk in moderately contaminated sediments. Integr Environ Assess Manag 2018;14:212-223. © 2017 SETAC.

Review of Polycyclic Aromatic Hydrocarbons (PAHs) Sediment Quality Guidelines for the Protection of Benthic Life

“…However, the data were from 9 different sites, and using a single K BC across sites is inconsistent with data from Hawthorne, Grabanski et al (), which showed that measured K BC values for individual PAHs vary by more than 2 orders of magnitude across different sites. These results are consistent with a field study by Brennan and Johnson () who found improved estimates of PAH toxicity and bioaccumulation were observed with the 2‐C model compared to the 1‐carbon (1‐C) model, highlighting the importance of BC and the limitations of using a 1‐C phase model to describe PAH partitioning. Nevertheless, dissolved porewater predictions derived using the 2‐C model overpredicted the importance of BC partitioning in some sediments.…”

“…Furthermore, the development of guidance for the use of passive sampling methods and standard protocols is leading to their growing use in site risk evaluations and acceptance by regulating agencies (USEPA 2017b). Consistent with the conclusions of Brennan and Johnson (2017), the use of direct porewater measurements determined through passive sampling techniques provides the logical path forward for refining benthic risk assessments, establishing improved remediation goals to protect benthic life, and assessing remedial effectiveness. preparation.…”

“…A method of correcting for DOC complexation when calculating freely dissolved chemical in porewater measurements is available (USEPA 2012). Passive sampling devices that quantify the freely dissolved concentrations are increasingly being applied to in-situ and ex-situ conditions to quantify the bioavailability of PAHs and other hydrophobic organics in sediments (Vinturella et al 2004;Cornelissen et al 2008;Lu et al 2011;Burgess et al 2015;Brennan and Johnson 2017). Passive sampling methods involve the partitioning of the chemical between the freely dissolved phase and an absorptive material.…”

Comparison of In Situ and Ex Situ Equilibrium Passive Sampling for Measuring Freely Dissolved Concentrations of Parent and Alkylated Polycyclic Aromatic Hydrocarbons in Sediments

“…Because no black carbon measurement was performed in the present study, we cannot rule out the presence or effect of black carbon for this comparison which could help explain the underestimated sorption of higher-log K OW substances. Several studies (Accardi-Dey and Gschwend 2002;Koelmans et al 2006;Ghosh 2007;Brennan and Johnson 2017;Endo et al 2020) underpin the hypothesis that the widespread occurrence of black carbon may reduce in situ bioavailability and thereby lead to order-ofmagnitude discrepancies between measured in situ concentrations and EqP-computed porewater concentrations noted in the present and previous studies.…”

“…By definition, a toxic unit is the bioavailable concentration of a single PAH (i.e., C free in porewater), divided by the corresponding final chronic value. Alternatively, EPSMs can be used to determine the C free of PAHs, directly avoiding the need to invoke EqP assumptions that can significantly overstate bioavailability due to increased sorption capacities of heterogeneous carbonaceous phases in sediments (Apell and Gschwend 2016; Brennan and Johnson 2017). Guidance has also been developed for applying this procedure to derive porewater‐based remediation goals (US Environmental Protection Agency 2017a).…”