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(429) Persistence of oil spilled from the T/V Exxon Valdez on beaches of Prince William Sound, Alaska, USA, after 12 years.
Short, Jeffrey*,1, Lindeberg, Mandy1, Harris, Patricia1, Maselko, Jacek1, Pella, Jerome1, Rice, Stanley1, 1 Auke Bay Laboratory, Alaska Fisheries Science Center, National Marine Fisheries Service, NOAA, Juneau, Alaska, USA
ABSTRACT- The rapid disappearance of oil from the surface of beaches three years after the Exxon Valdez oil spill implied that remaining oil would quickly disperse. Although this presumed rapid dispersal has been cited in criticism of recent reports claiming long-term toxic impacts of the spill to fauna that forage or reproduce intertidally, it has not been quantitatively confirmed. We therefore conducted an extensive field study of Exxon Valdez oil remaining in Prince William Sound (PWS) in summer, 2001, based on a representative probability-based sampling design. We selected 91 beach segments at random from 3 mutually-exclusive categories of oiled beaches surveyed during 1989-1993, and excavated 6,775 quadrats each 0.25 sq. m and up to 0.5 m deep placed according to a stratified random sampling design among the selected beach segments, at tidal elevations ranging from +1.8 m to +4.8 m. We found Exxon Valdez oil on 53 of the selected beaches, as surface oil in 226 quadrats and as subsurface oil in 347 quadrats. We estimate the equivalent of 3.94 ± 1.14 ha (± SE) and 7.99 ± 2.36 ha of beach remained oiled by surface and subsurface oil. The combined oiled area (correcting for overlap) was 11.4 ± 2.25 ha, over twice the oiled area measured in 1993. Most of the surface oil was present as weathered asphalt pavements, soft surface oil residues or surface sheens. Subsurface oil was present as a fluid light oil residue in 62% of subsurface oiled quadrats, followed by fluid medium oiled residue (21%), oil film (11%) and fluid heavy-oil residues (6%). Subsurface oil was most prevalent in the more biologically productive mid- and lower-intertidal, in contrast with surface oil. The total volume of oil remaining in 2001 is estimated as about 65,000 L, or about 8% of the volume estimated remaining in 1992, indicating annual dispersion on the order of 22%. Although the decline in volume has reduced the intensity of oiling in sediments, the decline has not been sufficient to appreciably reduce the area of oiled sediments. The remaining subsurface oil contains suites of polycyclic aromatic hydrocarbons (PAH) that are readily available biologically, and is most prevalent in beaches that were most heavily oiled initially. These beaches are most abundant in bays where evidence for long-term toxic effects of oil has been indicated.
Key words: Oil, Toxicity
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