EVALUATION OF RESIDUAL POLYCYCLIC AROMATIC HYDROCARBONS IN SEDIMENTS FOLLOWING A SPILL OF DILUTED BITUMEN

Crude oils consist of inherently complex mixtures of hydrocarbons of variable structures and molecular weights, resulting in unique mixtures. The bitumen portion of crude oil most commonly consists of immobile hydrocarbons that require unconventional extraction techniques and dilutants to mobilize it for transport. Polycyclic aromatic hydrocarbons (PAHs), a chemical group commonly found in this portion of crude oil, are known to pose human and ecosystem threats. Increased transport of diluted bitumen, along with subsequent pipeline breaks/spills, has stimulated the need to understand better the persistence and fate of PAHs in the environment. This study sought to evaluate the presence of PAHs in sediment impacted by the 2010 pipeline rupture of approximately 843,000 gallons of diluted bitumen from Canada’s Athabasca tar sands oil field into the Kalamazoo River near Marshall, MI. Approximately 5 years after the spill, riverbank sediments were collected for detection of PAHs. Most of the collected samples were from remediated/reworked sediments directly impacted by the initial spill and extensive clean-up process. Samples were analyzed for the presence of PAHs using GC-FID, and results were compared to those collected both upstream and downstream of the spill site. PAHs commonly associated with diluted bitumen (ex. naphthalene, acenapthene, flourene) were detected in nearly all samples impacted by the spill, regardless of grain size fraction, with concentrations being notably higher in the impacted area. For example, concentrations of acenaphthene, a biomarker for Athabasca tar sands oil, ranged from 1.9-4.9 ppm in samples collected from the remediated spill area, while samples from nearby locations both upstream and downstream of the rupture had no detectable concentrations. Laboratory microcosms consisting of native sediments and water from the impacted area were subsequently constructed to evaluate the changes in PAH concentration and accumulation of degradation byproducts over time. Preliminary results indicate recalcitrant behavior of PAHs with a prolonged release of a variety of hydrocarbon compounds that may pose long-term environmental threats. Results indicate that, despite remediation efforts, PAHs are persisting in the impacted sediments and may pose long-term water quality issues