Distribution And Sources Of Polycyclic Aromatic Hydrocarbons In Urban Surface Soils Of Kunming

Polycyclic aromatic hydrocarbons (PAHs) represent a group of carcinogenic, teratogenetic and mutagenic contaminants recognized as persistent organic pollutants (POPs) for their toxicity, bioaccumulation, semi-volatility and persistence. PAHs are wide spread in air, water, soils, sediments, food and organism. In recent years, PAHs have attracted intense scientific interest due to their wide distribution and great harmfulness. Many contries and organizations have built different laws to control over PAHs. To prevent organic pollution and satisfy the needs of environmental quality assessment, extensive investigations on PAH concentration, distribution and sources identification have been carried out. In this paper, the concentrations, distribution, possible sources and potential risk of PAHs in urban surface soils were studied in Kunming, situated in a lake basin of the Yunnan-Guizhou plateau.A method for simultaneous determination of the15PAHs (ACY, ACE, FLO, PHE, ANT, FLA, PYR, BaA, CHR, BbF, BkF, BaP, DaA, IcdP and BghiP) in Kunming's urban surface soils by microwave-assisted extraction (MAE), gel permeation chromatography (GPC), solid phase extraction (SPE) and gas chromatography-mass spectrometry (GC/MS) was employed. The optimal clean up procedures were investigated using GPC and SPE. The cleanup of extracts was carried out by GPC on a Biobeads S-X3column with cyclohexane/ethyl acetate (1:1, v.v) as mobile phase. Target compounds were eluted in the fraction from11-25min retention time. Moreover, the cleanest extracts were obtained by SPE with C18cartridges after the elution with12mL dichloromethane. The method was validated by spiked samples which showed good recovery and reproducibility. The overall recoveries ranged from58.33%-88.17%, with relative standard deviations (RSD) of3.26%-16.29%.15PAHs were analysed in40surface soil samples (0-5cm layer) collected from6types of land uses in the Kunming urban area. One-way analysis of variance (ANOVA) was employed to analyse the difference of PAHs pollution among the six districts. The correlation coefficients between concentrations of PAHs and soil TOC were calculated. Meanwhile, the potential sources of PAHs in surface soils of Kunming have been investigated by PAH isomer ratios and principal component analysis (PCA). The toxic equivalent (TEQ) of each sample was calculated based on the toxic equivalence factors (TEFs) of PAHs, which were used to quantify the carcinogenicity of other PAHs relative to BaP.(1) The total concentration of15PAHs ranged from101.64-6208.25ng/g, with a mean of1132.82ng/g. The concentrations in different land uses increased in an order as:green space (541.43ng/g)<education area (756.49ng/g)<business area (810.17ng/g)<residential area (1034.36ng/g)<industrial area (1166.79ng/g)<roadside greens (2146.76ng/g). Kunming's urban soils have been polluted by PAHs in various degrees and half of the samples were classified as contaminated or heavily contaminated. When compared with other cities, the concentrations of Kunming's urban soils were classified as a moderate level.(2) Visible differences existed among different land uses for individual compounds, excepting for ACY, ACE, FLO and ANT. Meanwhile, PHE, FLA, PYR, CHR and BbF were the most abundant individual PAHs in urban soils all for the six districts. The similar compositions indicated that the pollutants might come from the same sources.(3) The correlation analysis indicated that neither individual nor total PAHs in soil samples were not correlated with TOC. It may be due to the result of non-equilibrium adsorption between TOC and PAHs. The PAH concentrations in Kunming's urban soils are mainly affected by the sources.(4) The results of sources identification suggested that PAHs in surface soils of Kunming urban area were greatly affected by combustion activities, especially the combustion of coal and liquid fossil fuel. Petroleum sources may exist in certain sample sites.(5) TEQ in40soil samples ranged from4.39to717.06ng/g. Compared with other criterions and researches, risk level of PAHs in Kunming's urban soils was low as a whole, and the higher risk levels were observed in the samples from roadside greens.