TOXICITY ASSESSMENT OF OIL SPILL AFFECTED GROUNDWATER: DIRECT IN VITRO ASSESSMENT AND TOXCAST-BASED EXPOSURE-ACTIVITY RATIOS (EARS)

In 1979, a crude oil pipeline stretching from south-central Alberta, Canada to Superior, Wisconsin, USA ruptured just outside of Bemidji, Minnesota. This rupture released almost 11,000 barrels of crude oil into surrounding land and groundwater. Groundwater samples from this legacy crude oil spill site, which has been studied for over 40 years, were collected in 2018 to characterize the biological activity of aged, oil-spill-affected groundwater. Water samples were collected upgradient and downgradient of the hydrocarbon plume and measured for physical and biogeochemical properties, including dominant redox zonation and organic chemistry. Samples were assessed for interaction with 48 human nuclear receptors (hNRs), and 24 g-protein coupled receptors (GPCRs) using Attagene’s FACTORIAL™ platform. These assays indicated upregulation of several transcription factor (TF; e.g., pregnane x receptor and aryl hydrocarbon receptor), NR (e.g., estrogen receptor), and GPCR (e.g., Prostaglandin D2 receptor) pathways by at least 20%. Upregulation levels as high as 45% were observed in samples taken at the start of the hydrocarbon plume versus sites farther downgradient, and no or minor upregulation of these targets was observed in upgradient background wells. GPCR data first obtained in 2019 mirrors the occurrence of upregulation in relation to well location which has been demonstrated by previous TF and hNR data (McGuire et al., 2018, Bekins et al., 2020). These results expand our understanding of molecular targets of oil-spill derived chemicals, and suggest that use of these bioeffects-based, high-throughput molecular tools can be used to assess effectiveness of remediation of petroleum-impacted sites. Historical chemistry data from this site are being analyzed to identify potential drivers of the observed biological activities. Specifically, toxicity data from ToxCast dataset are being used to calculate exposure-activity ratios (EARs) for the chemicals present in wells found throughout the hydrocarbon plume. Toxicity data from the CompTox Dashboard (https://comptox.epa.gov/dashboard/) will be evaluated using ToxEval package. We will calculate EARs for each of the chemical-molecular target combinations identified. This process will allow for prioritization of both, affected molecular targets and chemical actors in this system.