Evidence for long-range transport of a low to medium molecular-weight petroleum product off Central California, USA

Abstract

Suspended particles collected within southern Santa Maria Basin (CA, USA) during November 1991 contained unusually elevated concentrations of parent and alkylated polycyclic aromatic hydrocarbons (PAHs) and patterns in straight chain alkanes and saturated biomarkers (terpanes and steranes) indicative of contamination by a distilled petroleum product from a California-sourced oil. Because no active offshore oil and gas drilling was occurring at the time, and there was no record of diesel spills or evidence from previous samplings of discharges of diesel fuel-contaminated drilling muds, petroleum hydrocarbons in the suspended sediments likely were related to a source other than platform discharges. The timing as well as the hydrocarbon composition suggested the presence of a petroleum product (diluent) that was released from an oil field at Guadalupe, approximately 50 km north of Santa Maria Basin. To evaluate diluent contributions, the hydrocarbon composition of suspended sediments were characterized and compared to those of possible source materials, including diluent, formation oils, and well cuttings, using principal component analysis (PCA). Suites of saturated and aromatic hydrocarbons, enriched in the C{sub 13} to C{sub 23} range, contained in some suspended sediments were consistent with relative abundances of low to medium molecular weight components in diluent but were differentmore » from those in formation and seep oils. Results of the PCA support the compositional similarities between the diluent and affected suspended sediments. This suggests that a petroleum product was transported as an oil-particle mixture over long distances with relatively minimal degradation. Wide dispersion of diluent increased potential exposures of marine organisms to toxic lower molecular weight PAHs.« less