DISSOLVED- AND PARTICULATE-PHASE HYDROCARBONS IN INTERSTITIAL WATER FROM PRINCE WILLIAM SOUND INTERTIDAL BEACHES CONTAINING BURIED OIL THIRTEEN YEARS AFTER THE EXXON VALDEZ OIL SPILL

Abstract

ABSTRACT Buried oil residues in selected beaches that were heavily contaminated by the 1989 Exxon Valdez Oil Spill (EVOS) continue to leach oil-contaminated suspended particulate material (SPM) and dissolved-phase polycyclic aromatic hydrocarbons (PAH) into interstitial- and near-shore waters. Both are bioavailable forms of hydrocarbons that can be absorbed or consumed. On selected intertidal beaches in Prince William Sound (PWS) during June 2002, nearshore- and interstitial-water samples were collected during outgoing tides, first from a water depth of 10–15 cm above undisturbed sediments at water's edge and then from pits dug just above the waterline. At the time of collection, all samples were vacuum-filtered through 0.7-µm pore-size, glass-fiber filters using a Portable Large Volume Water Sampling System (PLVWSS) to separate dissolved- and oil-contaminated SPM fractions for detailed hydrocarbon analyses and fingerprinting. From intertidal pits at oil-impacted sites, interstitial water and SPM displayed strong oil signatures and elevated (albeit variable) PAH and n-alkane levels compared to the trivial non-petrogenic signatures seen at the reference sites. The dissolved-phase samples at the oil-impacted sites were typically characterized by water-soluble, lower-molecular-weight PAH, while the SPM/oil-phase contained the relatively-insoluble, higher-molecular-weight PAH and n-alkanes. Water's-edge samples (collected before any pits were excavated) typically showed a diluted- and degraded-compositional signature traceable to the interstitial water from higher tide levels. Interstitial-water dissolved-phase concentrations (average 1,200 ng/L.; 76–4,600 ng/L vs. 18–27 ng/L for reference sites) were above those reported to cause impacts to herring and salmon eggs (<1,000 ng/L; Rice et al., 2001). At reference sites, the water's edge samples matched the interstitial water with very low, non-petrogenic signatures. A recent diesel spill at a nearby site showed dissolved-phase patterns similar to those at the current EVOS sites.