Preliminary Investigation of Origin of Aliphatic Compounds in Street Dust Samples, Pančevo, Serbia

Abstract

The aim of this study was analysis of the origin of the aliphatic compounds in selected street dust samples. The samples were collected in the city of Pančevo, Serbia, within residential areas in close vicinity to heavy traffic roads. In order to determine if there was a significant difference in composition of aliphatic fraction depending on particle size, the samples were sieved and separated in three fractions, 500–250 µm, 250–63 µm and <63 µm. The samples were extracted, and the extracts were separated to aliphatic, aromatic and polar fractions by column chromatography. The aliphatic fractions were further analysed by GC/MS. n-alkanes were identified using mass ion m/z 71, hopanes m/z 191 and steranes m/z 217 [1]. Concentrations of total hydrocarbons in the street dust samples were in the range from 34.5 to 280.0 µg/g. It is generally accepted that total hydrocarbons content higher than 50 µg per 1g of sediment can be considered as a potential anthropogenic pollution [2]. According to these results, presence of organic pollutants in almost all samples can be presumed. Concentrations lower than 50 µg/g were observed in coarser fractions (500-250 µm). Higher concentrations of total hydrocarbons were observed in the finest fraction (< 63 µm). With only few exceptions, concentration of total hydrocarbons increases with decrease of grain size of samples indicating greater affinity of these compounds for the smallest particles. In all samples analysed, the most abundant compounds were n-alkanes, followed by n-alk-1-enes, regular isoprenoids and hopanes. No significant compositional changes were observed in different size fractions of the samples. n-Alkane distribution in all samples is bimodal, with n-alkane maximum at C20 in the range C13-C23, and with maximum at odd number n-alkanes in the range C24– C34. Carbon Preference Index (CPI) [2] for the whole range of n-alkanes (CPI C13-C33) is in the range of 1.07 – 2.40, CPI C13-C20 is close to 1, and CPI C25-C34 is in the range from 1.0 to 3.9. These results and distribution of n-alkanes in the chromatograms (Figure 1) indicate that the investigated n-alkanes in the C13-C23 range originate from a mature organic matter source while those in the C24–C34 range originate from the native terrestrial organic matter. Definite proof that the aliphatic fractions of the street dust samples contain petroleum pollutant can be seen by distributions of hopanes, steranes and diasteranes, which have typical distributions found in crude oils. It can be concluded that the aliphatic compounds in the street dust samples investigated in this study are mixtures of a natural terrestrial source (indicated by presence of even alk-1-enes and odd higher n-alkanes) and a petroleum pollutant (indicated by CPI values and presence of typical crude oil biomarkers)