δ [formula omitted] values of polycyclic aromatic hydrocarbons collected from two creosote-contaminated sites

Abstract

Groundwaters were sampled on two dates from several wells at each of two creosote-contaminated waste sites in Florida. Polycyclic aromatic hydrocarbons (PAHs) were extracted from the groundwaters, and their individual concentrations were measured by gas chromatography/flame ionization detection (GC/FID). The δ 13 C values of the PAHs were then determined by gas chromatography/ion trap mass spectrometry/isotope ratio mass spectrometry (GC/ITMS/IRMS). At the American Creosote Works (ACW) in Pensacola, concentrations of PAHs were found to decrease by over four orders-of-magnitude, both with increasing depth and with increasing distance from the most contaminated area. At a wood-preserving facility in Gainesville, concentrations were also found to decrease with increasing distance from the most contaminated area. At the ACW site, δ 13 C values of individual PAHs ranged from −20.09‰ to −32.94‰, although the majority of compounds fell in a tighter range between −22.66‰ and −25.31‰. The δ 13 C values of over 75% of the PAHs remained constant across all wells, both with migration of the contaminant plume and over a 3-month time period. The compounds that showed the highest variability among the wells were anthracene; the heterocyclic compounds thianaphthene, dibenzothiophene, and carbazole; and the lighter PAHs naphthalene, biphenyl, and 2-methylnaphthalene. Variability of these compounds is likely the result of variations in δ 13 C values among different creosotes added to the sites over many years. The other compounds measured were conserved across the wells and would serve as good tracers of a contaminant plume in bioremediation settings. At the Gainesville site, δ 13 C values of individual PAHs ranged from −18.87‰ to −27.05‰, with 70% of the values falling between −22.06‰ and −24.53‰. This range is very similar to the values for PAHs at the ACW site. Comparing δ 13 C values of specific PAHs between the two creosote-contaminated sites, 12 of 16 compounds agreed within 1.0‰. This indicates that, although there are a few compounds that may be variable across different creosotes, there may be a suite of δ 13 C values that is conserved across PAHs of creosote origin. These characteristic PAHs could be used to determine whether or not creosote is contributing to the PAH contamination at a site. In addition, the compounds that are variable between different creosotes could be used as tracers of individual creosotes at polluted sites and to differentiate between possible creosote sources.