Use of Parent Polycyclic Aromatic Hydrocarbon (PAH) Proportions to Attribute PAH Sources in Sediments: A Case Study from the Pacific Northwest

Abstract

Since the late 1970s, a large body of scientific literature has developed focused on attributing sources of polycyclic aromatic hydrocarbons (PAHs) in sediments. Forensic evaluation of sources of PAHs in sediments has typically relied on the use of the ‘expanded PAH’ analysis in which ‘parent’ (non-alkylated) and alkylated members of each homologous series are quantified and reported. Use of this method for source attribution is widely documented in the peer-reviewed literature and has gained wide acceptance in the forensics community. Although the expanded PAH analysis is the preferred method of using PAH data for source attribution, these detailed forensic data are often not collected during routine environmental site investigations. Conversely, the 16 United States Environmental Protection Agency “priority pollutant” PAHs, which include the parent PAH of each homologous series, are routinely analyzed for and reported. Because of the large number and relatively high costs of sediment and soil remediation projects focused on PAHs, there is significant interest in the use of these parent PAH data for forensic source attribution. The peer-reviewed literature contains a few case studies where parent PAHs have been used to attribute sources, including distinguishing between petrogenic (petroleum) and pyrogenic (combustion and pyrolytic) sources, and among multiple pyrogenic sources. This article focuses on a case study that demonstrates the use of parent PAH ratios or proportions for source attribution for PAHs in sediments offshore of a former wood treating facility located in a highly industrialized port of the northwestern United States. The wood-treating facility was assumed as the source for all of the PAHs present in the sediments; this assumption was questioned in the litigation brought to allocate costs for the sediment remediation. Because the sediment remediation was complete, additional sampling for sophisticated forensic testing was not possible; therefore, the forensics evaluation had to rely on the pre-existing parent PAH data. Using the forensic parent PAH proportions and ratios developed by Yunker et al. (2002) and those of Costa and Sauer (2005), PAHs in the sediments were categorized into those attributed primarily to the wood treating facility creosote and those attributed primarily to a mixture of pyrogenic and petrogenic sources common in the “urban background” of industrialized waterways. This approach provided a basis to propose cost allocation for each of the sediment areas that required remediation.