Geochemical changes in crude oil spilled from the Exxon Valdez supertanker into Prince William Sound, Alaska

North Slope crude oil spilled from the T/V Exxon Valdez in March 1989 and contaminated about 500 km of Prince William Sound shoreline. Aliphatic and aromatic hydrocarbons in oil samples collected in August 1990 and June 1992 from beaches on six islands impacted by the spill have been compared with the hydrocarbons from North Slope crude oil taken from the stricken tanker. Degradation processes have changed the physical appearance of this residual spilled oil; the beached oil as collected ranged from a light brown color, to a heavy black viscous oil, to a black, powder-like residue. In these physically different samples, terpane, sterane, and aromatic sterane distributions, as well as carbon isotope values, are similar and correlate with the original Exxon Valdez oil. On the other hand, n-alkanes, isoprenoids, and many of the polycyclic aromatic hydrocarbons which are present in the original crude oil are dramatically altered in the oil samples collected from the beaches.