TOXICITY ASSESSMENT OF CRUDE OIL CONSTITUENTS AND BREAKDOWN PRODUCTS IN THE PETROLEUM-IMPACTED GROUNDWATERS AT A BIODEGRADATION AND NATURAL ATTENUATION LEGACY SITE NEAR BEMIDJI MINNESOTA

Remediation of oil spills requires not only an understanding of the physical, chemical, and biological processes affecting chemical fate and transport but also an understanding of the toxicological endpoints that determine the risk to human and ecosystem health. Recent research indicates waters impacted by petroleum hydrocarbons may exhibit a variety of biological activities that can lead to adverse health effects. Here, we report data from the Bemidji Crude Oil Spill legacy site where 38 years ago, 10,700 barrels of crude oil were released and still, the oil and its breakdown products (metabolites) remain in the subsurface. Water samples were collected from various contamination levels within the hydrocarbon plume and measured for physical and biogeochemical properties, including dominant redox zonation and organic chemistry. The waters were then assessed for: 1) acute toxicity (in situ, raw samples, Microtox®, N=30), and 2) human nuclear receptor (NR) activity (solid phase extracted samples, 48 NRs evaluated using Trans-FACTORIAL™ platform, N=5). Up to 51% acute toxicity was observed in samples taken from more contaminated, methanogenic zones with relatively high concentrations of nonvolatile dissolved organic carbon (NVDOC) (e.g., 29.7 mg/L C). Acute toxicity was not observed in less contaminated or background samples from iron reducing zones with NVDOC concentrations of 3.3 mg/L C and 1.7 mg/L C respectively. In vitro NR assays indicated upregulation in a few predominant biological pathways including: peroxisome proliferator-activated receptor gamma and alpha (PPAR), estrogen receptor alpha (ERa), pregnane X receptor (PXR), and retinoid X receptor beta, (RXRb). Increased activation of these pathways may be linked to adverse impacts on development, endocrine and liver function. Similarly, higher levels of NR activity were observed in samples taken from methanogenic zones than those from iron-reducing zones within the plume, and no or minor upregulation of these targets was observed in background samples. These results expand our understanding of potential toxicity of petroleum-impacted waters and have implications for decisions involving the effectiveness of remediation of petroleum-impacted sites to protect human and ecosystem health.