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Polycyclic aromatic hydrocarbons in still creek sediments : distributions, concentrations and possible sources Morton, Teresa Anne


The extent of polycyclic aromatic hydrocarbon (PAH) contamination was determined in the stream sediments of an urban watershed, and some possible sources were investigated. Analytical methodology was adapted from the literature for determination of polycyclic aromatic hydrocarbons in sediments. Alkaline digestion of samples was followed by solvent-solvent partition and Florisil chromatography. An alumina column clean-up effected preliminary separation of compounds before determination using high pressure liquid chromatography (HPLC). Some extracts were also analyzed on a capillary gas chromatography system and by capillary gas chromatography mass spectrometry (GCMS) to provide additional qualitative information as a result of the much improved resolution. Samples of stream sediments were obtained from Still Creek in the Brunette River watershed. Analysis for PAH in sediments from five sampling sites (sampled two consecutive years) revealed that all sediments contained a wide range of PAH. While the profile of the extracts (by HPLC) was remarkably similar from site to site, and from the first to second year, the amounts of PAH present varied by two orders of magnitude among sites. Levels of individual compounds quantitated ranged from mid part per billion (55 ppb) to mid part per million (38.5 ppm) . PAH identified by HPLC analysis (eleven compounds) were mainly non-alkylated parent compounds, but GCMS data indicated that many alkyl-substituted or heteroatom polycyclics were also present. Preliminary investigations of PAH levels found in oligochaetes indicated bioconcentrations of some compounds, and suggested a possible competition for PAH among high organic content sediments and the live oligochaetes present. Investigation of possible sources of polycyclics aromatic hydrocarbons to stream sediments included street surface contaminants and crankcase oil. Street sediments exhibited HPLC elution profiles strikingly similar to those of stream sediments. Levels of PAH found were slightly lower than, but comparable to, concentrations in stream sediments, and the same individual compounds were quantitated in each type of sample. Thus the street sediments were determined to be an important source of PAH to stream sediments, with transport occurring through urban street runoff. Crankcase oil demonstrated a linear buildup of PAH with mileage over approximately the first 2000 km, then a leveling off occurred. Based on HPLC profiles, used crankcase oil contributes to street surface contamination. Regression analysis of total PAH levels in various samples failed to provide significant correlations with location of sampling point (on stream), traffic volume at sampling point, land use (for street sediment samples) or sediment characteristics. However, sediment characteristics (particle size, organic content) were identified as being the most important of the factors considered. Implications of the presence of a PAH burden in the stream sediments (comparable to other older, larger urban watersheds) were discussed with relation to natural systems. Recommendations were made for study to further elucidate PAH sources and transport to stream sediments.

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