Aliphatic and polycyclic aromatic hydrocarbons (PAHs) in soils of the northwest Qinling Mountains: Patterns, potential risk and an appraisal of the PAH ratios to infer their source

ABSTRACT

Surface soils from the tourist areas of the northwest Qinling Mountains were analyzed to determine the concentrations, probable sources and potential risks of hydrocarbons. Concentrations of aliphatic and aromatic hydrocarbons ranged from 4.18 to 3240 ng g⁻¹ and 0.0462 to 101 ng g⁻¹ dry weight, respectively. The extent of soil contamination by hydrocarbons was generally typified by unpolluted to slightly polluted levels. The incremental lifetime cancer risks (ILCRs) for exposure to soil-borne PAHs indicated complete safety for tourists. Early diagenesis of natural products, bacteria activities and petroleum were the three main sources of aliphatic hydrocarbons, while the transport of air pollutants from pyrolytic processes was the main origin of PAHs. Because the photochemical reaction of PAHs in the atmosphere would produce lower ratios for Ant/(Ant + Phe), BaA/(BaA + Chr) and IcdP/(IcdP + BghiP), but a higher ratio for Fla/(Fla + Pyr), the source classification highly depended on the diagnostic ratios chosen. The plot of ΣCOM/Σ₁₃PAH vs. ΣLMW/ΣHMW_PAH provide additional information to distinguish the origins of PAHs, and it showed a cluster of pyrogenic sources except for sample JFS-8. Four sources were resolved by principal component analysis: (1) a low temperature pyrogenic process related to the use of fossil fuel and biomass, such as charcoal, straw and wood, which contributes 63.1% of the measured PAHs; (2) the potential contribution of diagenetic processes, contributing 18.4%; (3) traffic emissions, contributing 9.27%; and (4) bioconversion/bacterial action, contributing 5.82%. Additionally, there was a good exponential relationship (r² = 0.969) between the natural n-alkanes ratio (NAR) and carbon preference index for C₂₃–C₃₅ (CPI_23–35) for all samples, which is of great use for the determination of the origins of aliphatic hydrocarbon.

KEYWORDS:

• Pollution monitoring
• risk assessment
• soil hydrocarbons
• source diagnostic ratios
• the northwest Qinling Mountains

Acknowledgments

Professor Yufeng Jiang (Lanzhou Jiaotong University) is gratefully acknowledged for the experiment and manuscript improvement.

Funding

This study was financially supported by the National Natural Science Foundation of China (41272147, 41172169 and 41202093) and the Key Laboratory for Oil and Gas Resources of Gansu Province Open-end Foundation (No. Y621JJ1WYQ;Y530JJ1WZD).