Carbon isotopic composition of polycyclic aromatic hydrocarbons and their weathering in Kachemak Bay sediment

Abstract

Identification of sources of polycyclic aromatic hydrocarbons (PAH) in sediments is an important step in reducing anthropogenic contamination. Identifications based solely on the composition of PAH can be confounded by compositional changes during weathering and biodegradation. Stable isotopic composition of individual PAH offer a source marker that may be less susceptible to alteration. The [alpha]¹³C values of PAH in major potential sources to the Kachemak Bay area were analyzed. To determine the stability of the [alpha]¹³C values of PAH in crude and diesel oil, microbial degradation experiments using sediment from the Kachemak Bay, Alaska, area were conducted over a one-year period. The impact of weathering on the isotopic composition of North Slope crude oil and diesel oil was also examined over a five-week period in aquaria with Macoma balthica, an intertidal bivalve. For both degradation experiments, PAH concentrations decreased and their composition changed, but the [alpha]¹³C values of individual PAHs remained stable. Hence, [alpha]¹³C values of individual PAHs have excellent potential as a relatively stable indicator of their sources. Based on isotopic and compositional data, the PAH in Kachemak Bay sediments appear to have several sources.