Complex mixture toxicology: Evaluation of toxicity to freshwater aquatic receptors from biodegradation metabolites in groundwater at a crude oil release site, recent analogous results from other authors, and implications for risk management.

Aquatic toxicity posed by the complex mixture of biodegradation metabolites and related oxygen-containing organic compounds (OCOCs) in groundwater at typical petroleum release sites is of concern to regulatory agencies; several are using results from laboratory studies in older literature that are not appropriate analogs for risk management. Recent field studies from typical sites and natural groundwater should be utilized. In this study, OCOCs downgradient of the biodegrading crude oil release at the USGS Bemidji site were tested for freshwater aquatic toxicity using unaltered whole groundwater samples.

Biodegradation of petroleum hydrocarbons in a weathered, unsaturated soil is inhibited by peroxide oxidants.

Field-weathered crude oil-containing soils have a residual concentration of hydrocarbons with complex chemical structure, low solubility, and high viscosity, often poorly amenable to microbial degradation. Hydrogen peroxide (HO)-based oxidation can generate oxygenated compounds that are smaller and/or more soluble and thus increase petroleum hydrocarbon biodegradability. In this study, we assessed the efficacy of HO-based oxidation under unsaturated soil conditions to promote biodegradation in a field-contaminated and weathered soil containing high concentrations of total petroleum hydrocarbons (25200 mg TPH kg) and total organic carbon (80900 mg TOC kg).