Distribution and Weathering of Crude Oil Residues on Shorelines 18 Years After the Exxon Valdez Spill

Abstract

In 2007, a systematic study was conducted to evaluate the form and location of residues of oil buried on Prince William Sound (PWS) shorelines, 18 years after the 1989 Exxon Valdez Oil Spill (EVOS). We took 678 sediment samples from 22 sites that were most heavily oiled in 1989 and known to contain the heaviest subsurface oil (SSO) deposits based on multiple studies conducted since 2001. An additional 66 samples were taken from two sites, both heavily oiled in 1989 and known to be active otter foraging sites. All samples were analyzed for total extractable hydrocarbons (TEH), and 25% were also analyzed for saturated and aromatic hydrocarbon weathering parameters. Over 90% of the samples from all sites contained light or no SSO at all. Of samples containing SSO, 81% showed total polycyclic aromatic hydrocarbon (TPAH) losses greater than 70%, relative to cargo oil, with most having >80% loss. Samples with SSO were observed in isolated patches sequestered by surface boulder and cobble armoring. Samples showing lowest TPAH loss correlated strongly with higher elevations in the intertidal zones. Of the 17 atypical, less-weathered samples having less than 70% loss of TPAH (>30% remaining), only two were found sequestered in the lower intertidal zone, both at a single site. Most of the EVOS oil in PWS has been eliminated due to natural weathering. Some isolated SSO residues remain because they are sequestered and only slowly affected by natural weathering processes that normally would bring about their rapid removal. Even where SSO patches remain, most are highly weathered, sporadically distributed at a small number of sites, and widely separated from biologically productive lower intertidal zones where most foraging by wildlife occurs.

Long-term effects of the ‘Exxon Valdez’ oil spill: sea otter foraging in the intertidal as a pathway of exposure to lingering oil

“…Thus, intertidal foraging provides a potential pathway of exposure to oil for sea otters and other nearshore species through direct contact with oil and/or through ingestion of contaminated prey , Short et al 2006, Boehm et al 2008. The pits left behind by foraging sea otters are evidence of their feeding activities, and are readily quantifiable through systematic beach sur veys.…”

“…We use surveys of foraging pits on beaches in oiled areas of WPWS and data from TDRs implanted in sea otters residing in these areas, along with published estimates of the distribution and abundance of lingering oil (Short et al 2006, Boehm et al 2008, to estimate the probability that sea otters inhabiting these areas may encounter oil while foraging in intertidal habitats. We had 4 objectives: (1) describe the extent of intertidal foraging by sea otters in WPWS, (2) estimate rates at which foraging sea otters encounter lingering oil, (3) estimate the frequency of occurrence of intertidal foraging pits dug by sea otters across soft-sediment bea ch es at northern Knight Island, where lingering oil is most common, and (4) quantify the concentration of total polycyclic aromatic hydrocarbons (TPAH) in sediments from intertidal foraging locations.…”

Cytochrome P4501A biomarker indication of the timeline of chronic exposure of Barrow’s goldeneyes to residual Exxon Valdez oil

“…Some of the oil released during the 1989 Exxon Valdez oil spill has remained in intertidal sediments of Prince William Sound, Alaska over the subsequent two decades (Boehm et al, 2008;Short et al, 2004;Short et al, 2006). Estimates of the quantity remaining (Boehm et al, 2008;Short et al, 2004) represent a small fraction of the oil that originally settled on Prince William Sound beaches following the spill (Wolfe et al, 1994), with residual oil in intertidal areas estimated to exceed 50,000 kg in 2001 (Short et al, 2004).…”

“…Estimates of the quantity remaining (Boehm et al, 2008;Short et al, 2004) represent a small fraction of the oil that originally settled on Prince William Sound beaches following the spill (Wolfe et al, 1994), with residual oil in intertidal areas estimated to exceed 50,000 kg in 2001 (Short et al, 2004). Concern and debate persist over whether vertebrates continue to be exposed to the remaining oil and, if so, whether that exposure negatively affects individuals or populations.…”

Exposure of sea otters and harlequin ducks in Prince William Sound, Alaska, USA, to shoreline oil residues 20 years after the Exxon Valdez oil spill

“…By environmentally significant amounts, we mean compositions and concentrations of and exposure durations to PAH that could harm wildlife, such as sea otters and harlequin ducks, that forage on the shore, as defined by risk-based concentrations of ingested individual and total PAH [16,17]. Polycyclic aromatic hydrocarbons are the chemicals of greatest toxicological concern in fresh and weathered petroleum [18,19] and represent approximately 1.2% by weight of the mass of organic matter in the unweathered North Slope (Alaska, USA), crude oil cargo of the Exxon Valdez [20].…”