So far, several studies have been carried out all over the world on the development of appropriate indicators for the emission of hydrocarbon contaminants and several indicators have been presented in this regard. These indicators are divided into internal and external categories. External indices determine the source of hydrocarbon pollution based on the ratio of metals in the oil, such as the ratio of nickel to vanadium. In contrast, indigenous indices, namely aromatic and aliphatic compounds, are used mainly for the propagation of hydrocarbon contamination. Because of the difference in reactivity, solubility, and thermodynamic properties between some polycyclic aromatic hydrocarbons isomers, they can be used to determine the source of hydrocarbon pollution.
Material and methods:
In many studies on hydrocarbon contamination, only one of the aliphatic or aromatic compounds in the water, soil and sediment environment is investigated. However, in this study, for the determination of hydrocarbon contamination in the south of Tehran, aromatic and aliphatic compounds were investigated in all water, soil, and sediment environments. To determine the amount of contamination, 33 samples of water, soil, and sediment were collected. After collection, the samples were immediately transferred to the laboratory and extraction of hydrocarbon compounds was done. Water samples were collected from wells, aqueducts, surface waters, and canals. Soil samples were obtained from surface and 50 cm depth of agricultural land, and primer soil and sediment samples were collected from sediments accumulated in canals, aqueducts and surface waters.
Results and discussion:
In this study, 16 important PAH compounds that are declared as carcinogenic by the US Environmental Protection Agency and aliphatic compounds (C8-C40) were studied. The average concentration of PAHs compounds in water samples was 2127.72 ppb ranging from 5 to 147125.56, in soil samples was 6715.7 ppb, ranging from 5 to 446642, and in sediment samples was957.77 ppb ranging from5 to11992.02. As for aliphatic compounds (C8-C40), their concentrationin water samples was 39.50 ppm with a range of 5-785.2, in soil samples was 1110 ppm with a range of 5-16160/74, and insediment samples was1751.13 ppm with a range of 5-30497.37. The presence of hydrocarbon contamination in the south ofTehran showed that petroleum pollution is petrogenetic. According to these results, the most contamination was observed insamples around the pond of oil waste and samples near the oil pipelines, where the hydrocarbon contamination can penetrateinto the groundwater and the soil. Also, the oil pollution in the area was not limited to the oil refinery, but part of it was relatedto the liquefied gas collection from the city and transportation to the canals to use for irrigation of agricultural land. Regardingthe comparison of concentrations of PAH and aliphatic compounds, the highest concentrations of PAHs were found in waterand sediment, respectively, and the highest concentrations of aliphatic compounds were in the soil, sediment, and water, respectively,respectively. Due to the fact that the hydrocarbon compounds in the water column are deposited into the channel depositsand these channels are periodically dredged by farmers in the region, there is no possibility of accumulation of high levels ofhydrocarbons in these environments. For this reason, the highest concentrations are in the soil environment.
The results of measurement and analysis of oil hydrocarbons in water, soil, and sediment environmentsshowed that oil pollution is petrogenetic. Most of this pollution is related to oil spills from Tehran refinery and the otherreason is the collecting channels of urban surface runoff, which are contaminated with petrogenetic petroleum compoundsthat lead to the south of Tehran.