Identifying sources of polycyclic aromatic hydrocarbons (PAHs) in soils: distinguishing point and non-point sources using an extended PAH spectrum and <Emphasis Type="Italic">n</Emphasis>-alkanes

Background, aim, and scope  Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous environmental pollutants. They are formed during pyrogenic and diagenetic processes and are components of petrogenic materials such as oils and coals. To identify PAH sources, several studies have employed forensic methods, which may be costly to execute. Although a large number of possible forensic methods are available (e.g., total ion chromatograms, PAH ratios, PAH alkyl homologue series, isoalkanes and isoprenoids, steranes and terpanes, stable isotope ratios, n-alkanes), one has to decide which method is the appropriate cost effective screening approach. In this study, three approaches were tested and compared by measuring (1) an extended PAH spectrum (i.e., 45 instead of the common 16 EPA-PAHs), (2) PAH ratios and (3) n-alkanes to determine if point sources are distinguishable from non-point sources, and if an individual source can be distinguished from a multiple source contaminated site in the study area. In addition, the study evaluated whether these methods are sufficient for source identification of selected samples, and if they constitute a sound strategy for source identification prior to the selection of more cost intensive methods. Materials and methods  Eighteen samples with previously characterized PAH point sources (previously characterized point sources in the Mosel and Saar region) were analyzed. Additionally, three river bank soils of Mosel and Saar rivers with known non-point PAH sources were investigated. The point sources were two gasworks, a tar impregnation facility, a creosoted timber, an acid tar, a tank farm, and a diesel contaminated site. Non-point sources were hard coal particles and atmospheric inputs in river bank soils. All samples were extracted with hexane and acetone, analyzed with a gas chromatograph coupled to a mass spectrometer for PAH distribution patterns and ratios. n-Alkanes were measured by a gas chromatograph equipped with a flame ionization detector. Results  Samples collected from point sources and non-point sources were analyzed by the use of three forensic methods, i.e., PAH patterns of an extended PAH spectrum, PAH ratios and n-alkanes. Identification by PAH patterns alone was insufficient for the non-point sources and some point sources, since the n-alkanes must be measured, as well. The use of PAH ratios with only 16 EPA-PAHs is less indicative in determining multiple sources because source assignments (or categories) change depending on the ratio used. Discussion  This study showed that by employing an extended PAH spectrum it is possible to fingerprint and distinguish sources. The use of alkylated PAHs is essential for identifying petrogenic sources. It is insufficient to rely exclusively on either the common 16 EPA-PAHs or the ratios to the parent PAHs when identifying non-point sources. Source identification using PAH ratios is only reliable if both parent and alkylated PAHs are measured. n-Alkane analyses provide more detailed information about petrogenic sources by verifying the presence of oils, diesel, gasoline, or coal in non-point sources. Conclusions  The three methods tested were deemed sufficient to distinguish between point and non-point PAH sources in the samples investigated. The use of an extended PAH spectrum provides the first step toward identifying possible sources. It simplifies the decision whether additional forensic methods should be necessary for more detailed source identification. Recommendations and perspectives  The determination of PAH alkyl homologue series, biomarkers, and isotopes is often advised (Kaplan et al., Environ Forensics 2:231–248, 2001; Oros and Simoneit, Fuel 79:515–536, 2000; Wang and Fingas, Mar Pollut Bull 47:423–452, 2003). The methods involved are complex and often expensive. We recommend a relatively uncomplicated and cost-effective method (i.e., extended PAH spectrum) before further and more expensive forensic investigations are to be conducted. Additional research with an extended sample set should be carried out to validate these findings for other sources and sites. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.