Research Article | Open Access
Larysa Mykhailova, Thomas Fischer, Valentina Iurchenko, "Distribution and Fractional Composition of Petroleum Hydrocarbons in Roadside Soils", Applied and Environmental Soil Science, vol. 2013, Article ID 938703, 6 pages, 2013. https://doi.org/10.1155/2013/938703
Distribution and Fractional Composition of Petroleum Hydrocarbons in Roadside Soils
Total petroleum hydrocarbon (TPH) concentrations and their fractional composition (medium fraction: n-alkane chain-length C15 to C27, heavy fraction: >C27) were determined at distances from 1 to 60 m from roads and at soil depths from 0.5 to 15 cm. The traffic intensities were up to 25000 vehicles per day. Soil TPH concentrations were highest within 15 m distance (665 and 3198 mg kg−1 at the windward and leeward sides, resp.), followed by a rapid drop to background values beyond (196 and 115 mg kg−1 in 60 m distance at the windward and leeward sides, resp.). The data variability was lowest at distances of 1 m and highest within tree plantations at distances of 15 m from the road. The TPH concentrations decreased with depth but were significantly higher than the background at all depths investigated. A principal component analysis revealed a positive relation between the medium-to-heavy fraction ratio and soil depth. A fractional differentiation of hydrocarbons with distance from road was not observed. It was concluded that the assessment of the potential of hydrocarbons to translocate, accumulate, or degrade in soil necessitates their subdivision into fractions based on their physicochemical and metabolic properties.
The widespread use of hydrocarbons in fuels causes their predominance among organic atmospheric pollutants, and petroleum products are the major source of anthropogenic hydrocarbon pollutants found in the atmosphere [1–3]. Total petroleum hydrocarbons (TPH) from fossil sources are not readily biodegradable as compared to biomass or soil organic matter, which have been demonstrated to be consumed during hydrocarbon degradation [4, 5]. Once deposited to the surface, hydrocarbons may persist and bioaccumulate in environmental media  and infiltrate into groundwater aquifers via leaching or into surface aquifers by runoff with severe effects on plants [7, 8], humans, and animals [9, 10]. Organic contaminants in roadside soils have been receiving considerable attention as a result of traffic intensity [1, 2, 11, 12]. Hydrocarbon deposition to ecosystems is of more complex nature, because it is influenced by meteorological and further peripheral conditions, like wind, geomorphology, road construction, buildings, or vegetation, resulting in atmospheric dilution, turbulent exchange, possible wind channeling, and so forth .
Apart from studies dealing with individual substances, TPH have been treated in the literature as one class of substances so far. However, as a diverse mix of numerous individual aliphatic hydrocarbons, components of petroleum products also behave individually in the environment. This consideration gives rise to our assumption that an investigation of translocation of TPH through and accumulation of TPH in environmental media must be based on their subdivision at least into fractions of substances with similar physical, chemical, and metabolic properties.
It is the aim of this study to prove the hypothesis that peripheral conditions, in particular vegetation, influence (I) amount and spatial variability of TPH in roadside soils and that the fractional composition of petroleum hydrocarbons changes with (II) distance from the road and (III) with soil depth.
2. Material and Methods
Soil samples were collected at distances of 1, 6–8, 15, 40, and 60 m and at depths from 0.5 to 15 cm in October 2010 from the Traktorostroiteley avenue in Kharkov (50°0′41′′N, 36°21′3′′E). Five replicates along a 100 m section at the windward and the leeward sides of the road, as referred to the long-term main wind direction (sides A and B, resp.), were sampled. A schematic map of the sampling location is given in Figure 1. At distances 3 of 8 m (windward side A) a single row of birch trees (distance between trees from 6 to 10 m) and 4 m (leeward side B) from the road a double row of maple trees (distance between trees from 4 to 6 m) were planted.
In addition, the Pushkinskaya street () and the M18 highway (pooled samples taken in October 2011, ) were taken into consideration for multivariate statistical analysis. An overview of the sampling sites is given in Table 1. The 60 m samples served as background level control. The soil type was Chernozem, developed on Loess at all sampling locations. The long-term mean annual precipitation in Kharkov is 520 mm, and the long-term mean annual temperature is 7.5°C. Plant litter and biomass are being removed from the surface twice per year in spring and in fall, and an organic soil horizon has not formed on top of the mineral mull horizon.
|Vehicles per hour, medium values from October 2010, 2according to Arbeitsgemeinschaft Boden , arithmetic mean values ± standard deviation. |
The samples were air-dried immediately after sampling to prevent microbial degradation of hydrocarbons. Total element concentrations were determined using energy-dispersive X-ray fluorescence spectroscopy (x-supreme EDXRF analyser, Oxford Instruments, UK). Total soil carbon was determined by dry combustion with O2 at 1050°C using a CNS Analyser (Elementar, Germany). Carbonates were determined volumetrically as CO2 after HCl treatment. Soil organic carbon was determined by subtraction of carbonate-C from total C.
TPH concentrations in soil were determined gravimetrically after triple extraction of 20 g sieved soil (<2 mm) with 50 mL hexane p.a., cleanup over a short aluminum oxide column, and solvent evaporation to constant weight at 40°C. TPH and fractional composition of petroleum hydrocarbons of selected samples were further determined using GC-MS (Carlo Erba, Fisons) after triple extraction of 2 g soil with 5 mL hexane for residue analysis, cleanup over a short fluorosil column, and solvent evaporation under hydrocarbon-free nitrogen at 20°C to a sample volume of 10–100 μL, depending on the results of the gravimetric hydrocarbon determination. Commercial diesel fuel and Hewlett Packard alkane standard Part number 18710-60170 were used for quantification and identification of total hydrocarbons and n-alkanes, respectively. We used an SGE HT8 column at 2 mL min−1 helium flow with 1 μL split injection at a split ratio of 20 : 1. Injection temperature was 300°C. The column temperature was 70°C during injection and was increased after 1 min with a heating rate of 30 K min−1 and held constant for 20 min after reaching 320°C. For detection we used positive electron impact ionization (EI+) at 70 eV and MS full scan mode with ranging from 50 to 250. A medium (C15 to C27) and a heavy fraction (>C27) were quantified in the chromatograms using the total ionic current (TIC) after elimination of siloxane signals resulting from column bleeding.
2.1. Statistical Analysis
Box-whisker-plots were used to depict median values (bold lines) and variation (upper and lower quartiles in boxes, data ranges as whiskers, outliers as circles) of TPH concentrations over distance from road. Principal component analysis (PCA) was performed to extract main components explaining the total data variability, where PCA biplots were used to identify correlations between variables. For PCA we used -transformed gravimetric and GC-MS TPH concentrations, soil organic carbon, Al, Fe, and Si concentrations, the distance from road, sampling depth, and the medium-to-heavy fraction ratio. Bivariate regression analysis, Pearson’s product moment correlation, and Student’s -tests were applied to check for statistical significance. We used the R software suite for all statistical calculations.
The highest TPH concentrations were observed within a 15 m strip along the road, followed by a rapid drop to background values beyond. At the leeward side, the TPH concentrations in 1 m distance from the road amounted to a median value of 3198 mg kg−1 and significantly (