Concentration distribution of polycyclic aromatic hydrocarbons (PAH’s) resulted from petroleum products in soils of the south Iran
Amir Bostani1, Amir Hossein Charkhabi2
1- Department of Soil Science, College of Agricultural Sciences, Shahed University, Tehran, 18151/159, Iran 2- Department of Environmental Engineering,Soil Conservation and Watershed Management Research
Institute, Iran
Corresponding Author:Amir Bostani
Abstract
Polycyclic aromatic hydrocarbons (PAH’s) are resulted by the incomplete combustion of fossil fuels and distributed in the environment including soil. This phenomenon is common in the south of Iran including the alluvial soils of Khuzestan province and has been addressed in this research work. Soil samples were collected from 200 different places in the province and using 1764 measurements, 16 carcinogenic PAH’s (µg kg-1), according to United States Environmental Agency (USEPA) guidelines, were determined. Soil parameters, influencing the results of this research work including salinity (ECe), acidity (pH), total organic carbon (TOC), total nitrogen (TN) and soil texture were also measured. The results indicated that the concentration of PAH’s in these soils were higher than the standard levels with a high variation ranging from 1 to 280 µg kg-1 and the average of 87.8 µg kg-1. For example, the amount of naphthalene in the soils ranged from 2 to 214 µg kg-1. There was significant difference in the concentrations of PAH’s between the southern and northern regions of the province. The concentration of PAH’s was higher in the surface soils in comparison with the subsurface soil. The high concentration of PAH’s in these soils reveal a considerable risk to human health and indicated the necessity of remediating these soils.
Keywords:Polycyclic aromatic hydrocarbons (PAH’s), Calcareous soils, Khuzestan province
Introduction
Polycyclic aromatic hydrocarbons (PAH’s) are a group of chemical compounds, bound through their aromatic carbons, forming linear, angular and cluster shapes. These compounds include a wide range of products from naphthalene with two aromatic structures to Cronin with seven aromatic structures (Olatunbosun et al., 2011; Sash, 1994). Based on the classification of environmental polluting materials, the first class PAH’s are resulted by human activities (Kavouras et al., 2001; Kulkarni and Venkataraman, 2000). According to United States Protection Environmental Agency (USPEA) out of the 120 known polluting compounds, 16 are PAH’s (Heitkamp and Cerniglia, 1988; Keith and Telliard, 1979). Most of these compounds are carcinogenic and their contact with human has been the subject of different research work (Liu et al., 2010; Walgraeve et al., 2010;
Yang et al., 2010).
Under natural conditions the presence of PAH’s in the soil is resulted by volcanic activities and plant residues with the concentrations ranging from 1 to 10g kg-1. Due to the increased concentrations of PAH’s in the soil they can enter the food chain affecting human health. Accordingly, the concentrations of PAH’s in the soil can be a useful indicator of environmental pollution. For example, the average concentration of PAH’s in the agricultural lands of South Korea has been equal to 236 mg kg-1, which is higher than the standard level (Menzie et al., 1992). For instance, the standard level, defined by the Dutch government, similar to the other industrialized countries, is in the range of 20 to 50 mg kg-1(Jones et al., 1989; Nam et al., 2003; Trapido, 1999).
The concentrations of PAH’s in the cities is significantly higher than the rural regions. In a research work on the soils of Beijing, the concentrations of sixteen PAH’s in 40 soil samples ranged from 16g kg-1 in the rural regions to 8843g kg-1 in the urban regions(Menzie et al., 1992). Such a high variation was attributed to the high number of vehicles and industrial activities (i.e. factories) in the cities(García-Alonso et al., 2013;
Olatunbosun et al., 2011). In another research work Veldre et al. (1979) studied on the soils of Estonia the total concentration of PAH’s in one of the industrialized cities with high petroleum sources and reported that PAH’s was much higher than the standard levels (12390 9810 g kg-1). The high concentration of PAH’s in these regions was due to the presence of petroleum sources resulting in the enhanced concentration of PAH’s in the atmosphere and hence in the soil (Veldre et al., 1979).
Usually the high concentration of PAH’s (about 70% of pollution) in the soil is attributed to the presence of petroleum sources. Considering the point that the presence of PAH’s in the soil is of health, economical and environmental significance the results of this research work can be of utmost importance (Tsai et al., 2010;
Walgraeve et al., 2010).
The province of Khuzestan has different sources of petroleum, resulting in atmospheric and soil pollution. Such results would be beneficial for the use of appropriate remediation and bio-remediation strategies to refine the environment. Accordingly, the objective of this research work was to determine the concentrations of PAH’s and their variations in the soils of Khuzestan, Iran.
Materials and methods Soil sampling
The distribution of soil samples is presented in Fig. 1. Due to the environmental importance of Shadegan Pond, more samples were collected from this area in comparison with the other areas. Soil samples were collected from the undisturbed surface soils, at the depths of 0-5, 10-15 and 40-50 cm (Fig. 1). Sampling was not performed in the highly polluted spots, because, as previously mentioned, the objective of this research work was to determine the large-scale range of PAH’s pollution in area. After collecting the soil samples, they were kept in sealed containers in a cold room and were prepared for further laboratory analysis.
Soil analysis
Soil samples were air dried and passed through a 2-mm sieve and analyzed for different physical and chemical properties(Bartels, 1996). Soil pH (using pH meter, model Meter Home) and conductivity (using conductivity meter, model Philips) were determined in the saturated soil paste. Soil organic carbon and texture were determined using the modified method of Nelson and Sommers (1982); Walkley and Black (1934) and the hydrometer method, respectively (Table 1).
Measuring PAH’s
The quantitative analysis of PAH’s was conducted using high performance liquid chromatography (HPLC), model Yanglin, equipped with a pump, model 9012 and a UV detector model 9050. The Autochrom software (version 4.2) was used. The solution used in the mobile phase was a compound with 20:80 (v/v) deionized water and acetonitrile. HPLC was first calibrated with the injection of standard solutions for PAH’s and then the samples collected from the extraction stage were injected to HPLC to determine their PAH’s concentration. Each injection was performed using a 100-L Hamilton syringe at the rate of 20 L. The maximum time for each chromatograph was 20 min. The HPLC software determined the concentration of PAH’s in the samples by comparing the standard graphs with the sample graphs and hence calculating this area ratios.
Results and discussion
The distribution of soil samples is presented in Fig. 1. Due to the environmental importance of Shadegan Pond, more samples were collected from this area in comparison with the other areas. According to Table 1, representing soil physical and chemical properties, soil salinity is high in these regions ranging from 25.8 to 34.98 dSm-1and decreases with depth. Soil organic matter was also little ranging from 0.8 to 1.4% with a
adsorption of PAH’s and hence reduce in destruction of its. This is also the case for the other colloidal particles such as clay in the soil. This indicates that in addition to the other effective parameters, the environmental impact of soil properties is also a determining factor affecting the unfavorable effects of PAH’s on the environment(Walgraeve et al., 2010).
Table 2 presents the statistical details regarding the PAH’s in the soil samples. The total concentration of PAH’s in depths of 0-5, 10-15 and 40-50 cm ranged from 9.1 to 241.9, 4.4 to 170.2 and 4.8 to 144.9g kg-1, respectively and the corresponding mean values were equal to 81.25, 55.5 and 37.5gkg-1, respectively. These averaged values was higher than the natural amounts in the soils with the range of 1 to 10g kg-1 (Edwards, 1983) and the values presented by the Dutch government (20-50g g-1 dry weight) (Van. Brummelen et al., 1996).
Based on Table 2 the PAH’s have a wide range of fluctuations and for naphthalene it is in the range of 2 to 214 g kg-1. Accordingly, the differences in the PAH’s concentration of the samples collected from the northern and the southern parts were statistically different. The geographical comparison of the collected samples indicated that the maximum concentration of PAH’ was related to the southern part, gradually decreasing toward the northern part (P= 0.05). The main reason for such a significant difference is related to the presence of petroleum sources in the region. In addition, the other factors such as soil, plant and climate properties can also result in such differences. According to Trapido (1999), the concentration of PAH’s in the petroleum regions of Estonia increased to more than 40 times higher, related to the nearby rural areas.
Fig. 2 presents the concentration of each PAH in the three different depths, indicating the higher concentration of PAH’s in the surface soil and their gradual decrease with depth (P= 0.01). The main reasons for the increased concentration of PAH’s on the soil surface is the precipitation of PAH’s on the soil surface, the polluted atmosphere, and precipitation, especially in the industrialized and polluted areas(Lv et al., 2010; Nam et al., 2003; Trapido, 1999). Park et al. (1990) indicated that the PAH’s with three or higher rings in their structure can be highly adsorbed by the leached soil particles and have a little solubility and vapor pressure. Accordingly, and with respect to the low amount of rain in the region, such type of PAH’s distribution in the soil is very likely.
Fig. 3 indicates the total concentration of PAH’s including the two-, three-, four-, five and six-ring structures in the depths of 0-5, 10-15 and 40 to 50 cm. Accordingly, 55.6 to 60.1% of the PAH’s total concentration is related to the two-ring structures (naphthalene), 31.1 to 36.1% is related to the three- and four- ring structures and 8.7 to 10% is related to the five and six ring structures. Naphthalene is a very important PAH, and is found in high amounts in petroleum compounds(Liu et al., 2011). The highest percentage of PAH’s is related to the two- and three- ring structures including naphthalene (a two-ring structure) with the highest percentage, followed by stanephten and stanephtylene(Irwin, 1997). Although naphthalene is insoluble in water, it is more soluble than the other PAH’s. Hence, its increased concentration in soil organic matter and its complex formation with the domain of soil clay particles is predictable resulting in the enhanced stability of this product in the soil. It has been indicated that the adsorption of naphthalene by soil particles including clay follows a Langmuir isotherm pattern (Liu et al., 2011) Such kind of property is of practical use for the remediation of soils polluted by PAH’s.
Table 1. The mean values and related standard error values for different soil physical and chemical properties, at different depths, for the alluvial soils of Khuzestan province, Iran. The values inside brackets represent the number of samples.
Soil depth (cm) 0-5 10-15 40-50
EC (dSm-1) 34.97±45.7 (92) 29.0±34.3 (92) 25.8±24.8 (91)
pH 7.7±0.4 (92) 7.7±0.4 (92) 7.6±0.3 (91)
OM (%) 1.4±1 (92) 1.0±0.6 (92) 0.8±0.6 (91)
Clay (%) 27±13.1 (131) 27.9±13.8 (134) 29.8±14.1 (128)
Silt (%) 46.9±18.5 (131) 45.3±19 (134) 42.4±18.8 (128)
Sand (%) 26.1±24.1 (131) 26.7±25.2 (134) 27.8±25.8 (128)
EC: electrical conductivity, OM: organic matter,
Table 2. The concentration of PAH’s (gkg-1) in the soils of region.
PAH’s Abundance Mean Max. Min. S.D.
Naphtalene(Na) 222 49.91 214 2 44.0
Acenaphthyln(Acy) 22 4.90 10 2 2.03
Acenaphthene(Ace) 52 7.92 220 1.3 30.1
Fluorene(Fl) 126 3.19 170 0.2 15.05
Phenanthrene(Ph) 226 3.53 17 0.1 2.89
Anthracene(An) 208 1.24 6 0.1 0.97
Fluoranthene(Flu) 220 2.42 10 0.1 1.84
Pyrene(Pyr) 238 3.53 280 0.1 18.11
Benzo[a] anthracene(BaA) 89 1.41 3.9 0.1 1
Chrysene(Chr) 141 2.12 7.4 0.1 1.73
Benzo[b] fluoranthene(BbF) 74 1.41 6 0.2 1.30
Benzo[k] fluranthene(BkF) 57 1.41 5.1 0.1 1.31
Benzo[a] pyrene(BaP) 47 1.69 6 0.2 1.57
Indeno[1,2, 3-cd]pyrene(InP) 18 0.69 3.5 0.1 0.83
Dibenzo[a,h] anthracene(DBA) 18 1.48 5 0.3 1.12
Benzo[g,h,I] perylene(BghiP) 6 0.95 1.9 0.2 0.7
Total 1764 87.8 280 0.1 12.8
Max: maximum, Min.: minimum, S.D.: standard deviation
Fig. 2. The concentration of PAH’s at three different depths (0-5, 10-15 and 40-50 cm) in the alluvial soils of Khuzestan province, Iran.
Fig. 3. The concentration of different forms of PAH’s at the depth of 0-5, 10-15 and 40-50 cm.
0 20 40 60 80 100 120
0-5 cm 10-15cm 40-50cm
Depth (cm)
Mean Concentration(µg kg-1) ∑PAH 2 ring PAH 3--4 PAH 5--6 PAH 0-5cm
0 10 20 30 40 50 60 70
Na Acy Ace Fl Ph An Flu Pyr BaA Chr BbF BkF BaP InP DBA BghiP
PAHs Mean Concentration(µg kg-1)
10-15cm
0 10 20 30 40 50 60 70
Na Acy Ace Fl Ph An Flu Pyr BaA Chr BbF BkF BaP InP DBA BghiP
PAHs Mean Concentration(µg kg-1)
40-50cm
0 10 20 30 40 50 60 70
Na Acy Ace Fl Ph An Flu Pyr BaA Chr BbF BkF BaP InP DBA BghiP
PAHs Mean Concentration(µg kg-1)
Conclusion
The results of this research concluded that the concentration of PAH’s in the soils of Khuzestan province is much higher than the standard levels. Hence, such products can have some serious environmental effects through the distribution of soil dust and their contact with people and other organisms including crop plants. Accordingly, it is very important to evaluate the properties of PAH’s including their concentration in the polluted areas and the nearby regions, such as petroleum, refinery and factory areas. Also, the province of Khuzestan is almost a highly populated area and the main reasons for such kind of soil pollution are the presence of petroleum and other industrialized areas as well as the incomplete combustion of petroleum in such areas. According to the results, more than 23% of the total weight of petroleum is related to the PAH’s. Thus, 70% of soil pollution with these products is resulted by petroleum collection and processing. Hence, it is important to evaluate the properties of such products in the soil so that their unfavorable effects are treated in a suitable way, which is of environmental and economical significance.
References
Bartels, J.M. 1996. Methods of Soil Analysis, Part 3: Chemical Analysis. Soil Science Society of America Inc. . American Society of Agronomy Inc. Madison. WI, USA.
Edwards, N.T.J 1983. Polycyclic aromatic hydrocarbons (PAHs) in the terrestrial environment, a review. J Environ Qual 12: 427-441.
García-Alonso, S, R. M Pérez-Pastor, A García-Alvarez and F. J. García-Frutos 2013. An approach to uncertainty estimation in determining polycyclic aromatic hydrocarbons in fuel- contaminated soils Toxicological & Environmental Chemistry 95: 26-37.
Heitkamp, M.A. and C.E. Cerniglia 1988. Mineralization of polycyclic aromatic hydrocarbons by a bacterium isolated from sediment below an oil field. Appl Environ Microbiol 54: 1612-1614.
Irwin, R.J. 1997. Environmental contaminants Encyclopedia. In Environmental contaminants Encyclopedia, ed.
Water Operations Branch 1201 Oakridge Drive National Park Service.Water Resource Divisions, Naphthalene Entry. Suite 250 Fort Collins: Colorado 80525.
Jones, K.C., J.A. Stratford, K Waterhouse, . , E.T. Furlong, W. Giger, R.A. Hites, C. Schaffner and A.E.
Johnston 1989. Increases in the polynuclear aromatic hydro-carbon content of an agricultural soil over the last century. Environ Sci Technol 23: 95-101.
Kavouras, I.G., P. Koutrakis, M. Tsapakis, E. Lagoudaki, E.G. Stephanou, D.V. Baer and P. Oyol 2001. Source apportionment of urban particulate aliphatic and polynuclear aromatic hydrocarbons (PAHs) using multivariate methods. Environ Sci Technol 35: 2288-2294.
Keith, L.H. and W.A. Telliard 1979. Priority Pollutants: I- a perspective view Environ Sci Toxicol 13: 416-423.
Kulkarni, P. and C.h. Venkataraman 2000. Atmospheric polycyclic aromatic hydrocarbon in Mumbai, India.
Atmos Environ 34: 2785-2790.
Liu, G. , Y. Tong, J. Luong, H. Zhang and H. Sun 2010. A source study of atmospheric polycyclic aromatic hydrocarbons in Shenzhen, South China. Environ Mon Assess 163: 599-606.
Liu, J.J., X.C. Wang and B. Fan 2011. Characteristics of PAHs adsorption on inorganic particles and activated sludge in domestic wastewater treatment. Biores Technol 102: 305-5311.
Lv, J., R. Shi, Cai. Y. and Y. Liu 2010. Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) Pollution in Soil of Suburban Areas in Tianjin, China. Bull Environ Contam Toxicol 85: 5-9.
Menzie, CA. , B.B. Potocki and J. Santodonato 1992. Exposure to carcinogenic PAHs in the environment.
Environ Sci Technol 26: 1278- 1284.
Nam, J.J. , B.H. Song, K.C. Eom, S.H. Lee and A. Smith 2003. Distribution of polycyclic aromatic hydrocarbons in agricultural soils in South Korea. Chemosphere 50: 1281-1289.
Nelson, D. W. and L. E. Sommers 1982. Total carbon, organic carbon, and organic matter. p.539-579. In: A. L.
Page et al. (ed.). Methods of soil analysis, part 2, 2nd ed. : ASA, SSSA, Madison, WI. .
Olatunbosun, S. Sojinu, O. Sonibare Oluwadayo and Y Eddy, Zeng 2011. Concentrations of polycyclic aromatic
Sash, L.B. 1994. Handbook of Marine Science: CRC Press Publication.
Trapido, M. 1999. Polycyclic aromatic hydrocarbons in Estonian soil: contamination and profiles. Environmental Poll 105: 67-74.
Tsai, J.H., S-.J. Chen, K.L. Huang, Y.C. Lin, W.J. Lee, C.C. Lin and W Lin, Y, 2010. PM, carbon, and PAH emissions from a diesel generator fuelled with soy-biodiesel blends. J Hazard Mat 179: 237-243.
Van. Brummelen, T.C. , R.A. Verweij, S.A. Wedzinga and C. Van Gostol 1996. Enrichment of polycyclic aromatic hydrocarbons in forest soil near a blast furnace plant. Chemosphere 32: 293-314.
Veldre, I.A. , A.R. Itra and L.P. Paalme 1979. Levels of benzo(a)pyrene in oil shale industry wastes, some water bodies of water in the Estonian S.S.R. and in water organisms. Environ Health Perspect 30: 211-216.
Walgraeve, C. , K. Demeestere, J. Dewulf, R. Zimmermann and H. Van Langenhove 2010. Oxygenated polycyclic aromatic hydrocarbons in atmospheric particulate matter: Molecular characterization and occurrence. Atmos Environ 44: 1831-1846.
Walkley, A. and I.A. Black 1934. An examination of Degtjareff method for determining soil organic matter and a proposed modification of the chromic acid titration method. Soil Sci 37: 29-37.
Yang, Y. , N. Zhang, M. Xue and S. Tao 2010. Impact of soil organic matter on the distribution of polycyclic aromatic hydrocarbons (PAHs) in soils. Environ Poll 158: 2170-2174.
