15 - Advances in forensic techniques for petroleum hydrocarbons: The Exxon Valdez experience

Abstract

Exxon Valdez oil spill (EVOS) in Prince William Sound (PWS), Alaska, is the most extensively studied spill in history. In the years immediately following the spill and continuing today, PWS and the adjacent Gulf of Alaska (GOA) has proven to be natural laboratories for the development and testing of new chemical forensic techniques for oil spill impact studies. Methods were developed for the quantification of both total mass loss and the chemical changes that occur in various fractions of shoreline oils as they weather. They confirmed that the inert asphaltenes and resin fractions make up an increasing fraction of the bulk oil as it weathers. Furthermore, they showed that all of the PAHs, including the 3- and 4-ring PAHs, are removed as weathering progresses, a feature of EVC not previously recognized. Multiple hydrocarbon inputs at oil spill sites are well documented, and an objective forensic approach should consider the possibility of other hydrocarbon sources; both anthropogenic and natural may exist. The application of advanced fingerprinting and geochemical forensic methods to chemistry data for intertidal and subtidal sediment samples identified and quantitatively resolved a number of hydrocarbon sources that contribute to the PWS marine environment: petrogenic hydrocarbons, pyrogenic hydrocarbons, and biogenic hydrocarbons.