Evaluating sedimentary PAH bioavailability based on equilibrium partitioning and passive sampling at the Dover Gas Light Superfund Site (Dover, Delaware, USA)

Abstract

From 1859 to 1948, the Dover Gas Light plant produced combustible gas for industrial, commercial, and residential applications using pine resin, coking coal, oil, and wood, and finally, a coal-gas process. Waste coal tar was discharged into the St. Jones River in Dover, Delaware (USA), via a ditch and culvert and, following plant closure in the 1940s, through groundwater flow from structures buried on the site. By the end of the 20th century, polycyclic aromatic hydrocarbon (PAH) contamination of the sediments in the St. Jones River was suspected to have occurred, and state and federal agencies initiated environmental assessments of the newly designated Superfund site. The current study investigated the spatial distributions of total PAHs in St. Jones River sediments adjacent to the site and evaluated their bioavailability. In 2017, 34 sediment cores were collected, sectioned, and analyzed using an on-site fluorometric screening technology indicating total PAH sediment concentrations ranging from 0.1 to 15 000 mg/kg (wet). A subset of cores involving 20 samples of various depths was selected and further analyzed by conventional GC/MS analysis for 16 parent PAHs. In addition, a 34-day in situ deployment of polyethylene passive samplers was performed to measure vertical bioavailability profiles of parent PAHs in sediments at three locations and overlying waters at four stations. Freely dissolved concentrations (C free ) of total PAHs were estimated based on equilibrium partitioning (EqP) of the GC/MS results and the passive sampling findings. C free values were used to calculate acute and chronic toxic units ranging from 1.4 to 56, based on EqP and 1.3 to 15 based on passive sampling. For six samples where comparative data were available, EqP calculations overestimated bioavailability by < 2-to 54-fold. Combining rapid field measurements with more accurate analyses of sediment concentrations and bioavailability in a tiered framework supported a time-efficient and cost-effective site investigation.

Potential Hazards of Polycyclic Aromatic Hydrocarbons in Great Lakes Tributaries Using Water Column and Porewater Passive Samplers and Sediment Equilibrium Partitioning

“…Under nonequilibrium conditions, the f eq for the amount of each PRC lost from the PED was calculated by Equation (2): $$<math xmlns="http://www.w3.org/1998/Math/MathML" altimg="urn:x-wiley:07307268:media:etc5896:etc5896-math-0002" display="block" wiley:location="equation/etc5896-math-0002.png" displaystyle="true"><mrow><mrow><msub><mi>f</mi><mrow><mtext>eq</mtext><mo>\unicode{x02212}</mo><mtext>PRC</mtext></mrow></msub><mo>\unicode{x0003D}</mo><mfrac><mrow><mo stretchy="false">(</mo><mrow><msub><mi>C</mi><mtext>PRCi</mtext></msub><mo>\unicode{x02212}</mo><msub><mi>C</mi><mtext>PRCf</mtext></msub></mrow><mo stretchy="false">)</mo></mrow><msub><mi>C</mi><mtext>PRCi</mtext></msub></mfrac></mrow></mrow></math>$$where f eq–PRC is the fractional equilibria for the PRC; C PRCi is the concentration of PRC in the PED at construction, and C PRCf is the concentration of PRC remaining in the PED after deployment (see the calculated f eq–PRC values in the Supporting Information, Tables S2 and S3). Our study was consistent with published guidance and other studies by using three representative PRCs covering a range of fugacities (Burgess et al, 2021; Choi et al, 2013; Fernandez et al, 2009; Ghosh et al, 2014; Reitsma et al, 2013; USEPA, 2017). Fernandez et al (2009) showed that the accuracy of using a few PRCs for assessing multiple target compounds was in good agreement with C free estimates when one was using target analyte–matched PRCs, thereby eliminating the need to have a full one‐to‐one PRC to target analyte match.…”

“…where f eq-PRC is the fractional equilibria for the PRC; C PRCi is the concentration of PRC in the PED at construction, and C PRCf is the concentration of PRC remaining in the PED after deployment (see the calculated f eq-PRC values in the Supporting Information, Tables S2 and S3). Our study was consistent with published guidance and other studies by using three representative PRCs covering a range of fugacities (Burgess et al, 2021;Choi et al, 2013;Fernandez et al, 2009;Ghosh et al, 2014;Reitsma et al, 2013;USEPA, 2017). Fernandez et al (2009) showed that the accuracy of using a few PRCs for assessing multiple target compounds was in good agreement with C free estimates when one was using target analyte-matched PRCs, thereby eliminating the need to have a full one-to-one PRC to target analyte match.…”

“…The PEDs were prepared by the Battelle Memorial Institute (Norwell, MA, USA) following internal standard operating procedure (SOP) 5‐366, Preparation of Polyethylene Devices for Deployment and Extraction. The PEDs consisted of 25‐µm‐thick low‐density polyethylene (LDPE) sheets that were cut to approximately 40‐ × 15‐cm size, cleaned using a mixture of organic solvents, and then spiked with performance reference compounds (PRCs; anthracene‐ d 10 , fluoranthene‐ d 10 , and pyrene‐ d 10 ; consistent with Burgess et al, 2021) using an 80% methanol to 20% water solution to determine equilibrium status and facilitate quantification of PAH concentrations (Ghosh et al, 2014). After 7 days of agitation in the spiking solution, the solution was drained and the PEDs were rinsed and soaked overnight in Milli‐Q water to remove any remaining spiking solution.…”

“…The ∑ESBTU is a common EqP‐based screening approach for potential toxicity of PAH mixtures in sediments (Burgess et al, 2021; Endo et al, 2020; Kemble et al, 2013). The ΣESBTU accounts for the OC content of the sediment and its effect on contaminant bioavailability, and is therefore considered to be applicable across a range of sediment types (USEPA, 2003).…”

“…Sorption to coal tar particles, when present, can be even greater (Khalil et al, 2006). As a result, in sediments high in BC or coal tar, EqP‐based toxicity assessments such as the ΣESBTU can overestimate C free , and thus PAH bioavailability and biological effects, by orders of magnitude (Arp et al, 2009; Burgess et al, 2021; Endo et al, 2020; McGrath et al, 2019). In recent years, improvements in passive sampling technology have facilitated the direct measurement of porewater PAH C free in sediments, potentially enabling more accurate estimates of biological effects compared with EqP‐based methods (Apell & Gschwend, 2014; Burgess et al, 2021; Endo et al, 2020; Fernandez et al, 2009; Mayer et al, 2014).…”