| Polycyclic aromatic hydrocarbons（PAHs） are a class of persistent organic pollutants（POPs）, generally existing in the environment medium, which are mainly caused by the incomplete combustion of organic materials or high temperature treatment and oil spill. Because of its hydrophobicity, carcinogenicity, teratogenicity, and biological degradability, attracted much attention and was seen as the main representative of POPs. After PAHs get into the atmosphere, they’ll get into the underground river system through the deposition and rain washing. Because PAHs are difficult to convert, the underground space may be the ultimate destination of PAHs, harming karst ecosystem. The PAHs in karst underground river system have different characteristics under the background of different human activities. Therefore, clarifying the composition, distribution, migration and pollution characteristics of PAHs under the background of different human activities and analyzing its origin is of great significance to improve the understanding of the pollution mechanism and prevent the pollution of PAHs in karst underground river system.This article selected the Laolong cave underground river catchment（LURC）and Qingmuguan underground river catchment（QURC）, Chongqing as the contrast research areas under the condition of industrialization, urbanization and agricultural activity. Through the field surveying of hydrogeology, land-use status and positioning sampling monitor, using gas chromatography/mass spectrometry（GC-MS） as the main analysis method, studying the distribution, composition and pollution characteristics, source and influence factors of PAHs in the surface karst spring, surface soil, underground water, and surface water, and assessing the ecological risk, which will provide a scientific basis of organic pollution prevention for karst areas. The results showed that:1. Concentrations, composition and pollution levels in water and surface soil in LURC and QURC. The PAHs concentrations in water of Shibazi spring, QURC ranged of 76.2473.6 ng·L-1, with a mean of 223.3 ng·L-1. The changes of concentrations showed the characteristics of concentrations in dry season were greater than the rainy season. The PAHs concentrations in surface water of Yankou, QURC ranged of 81.9420.9 ng·L-1, with a mean of 242.1 ng·L-1 and a large monthly dynamic change. For the underground river, the PAHs concentrations in water of Jiangjia cave and Jiangjia spring ranged of 73.9449.8 ng·L-1, 97.5480.3 ng·L-1, respectively, with a mean of 198.8 ng·L-1, 230.3ng·L-1, respectively.The PAHs profiles were dominated by（2-3） rings PAHs in water samples, accounting for 84.2% of the total PAHs contents. Which the PAHs with the average concentrations highest in water samples was Nap, reaching to 64.8ng·L-1. The PAHs pollution level was low, of which the concentrations of some low MW PAHs in all waters exceeded the limitation of the water quality standards, and only twice the concentrations of high MW PAHs in surface and outlet waters exceeded the limitation of the water quality standards.The PAHs concentrations in water of Laolong cave underground river ranged of 136.51407 ng·L-1, with a mean of 427.2 ng·L-1. The PAHs concentrations in water of Xiannü cave underground river ranged of 65.9887.9 ng·L-1, with a mean of 296.8 ng·L-1. PAHs concentrations in water of underground river showed the characteristics that the highest level appeared in early rainy season（April to June）, the lowest level appeared in late rainy season（August to October）, and the concentrations in dry season（November to March） were higher than contents in the late rainy season. The PAHs concentrations in water of Zhaojiayuanzi spring rangeed of 116376.1 ng·L-1, with a mean of 225.4 ng·L-1.The PAHs concentrations in water of Xiajiazui spring ranged of 90.41173 ng·L-1, with a mean of 353.2 ng·L-1. For the surface waste water, the PAHs concentrations in water of foul sewer and sewage treatment tank ranged of 334.8601.1 ng·L-1, 75.3813.6 ng·L-1, respectively, with a mean of 443.8 ng·L-1,291.3 ng·L-1, respectively. Sewage treatment plant for the removal of organic pollutants in wastewater played a role which can reduce the pollution of underground river, but the effects were far not enough. The PAHs profiles were dominated by（2-3） rings PAHs in water samples, accounting for 77.5% of the total PAHs contents. The PAHs with the highest average concentrations in water samples was Nap, reaching to 75.9ng·L-1. The concentrations of some low MW PAHs in waters of LURC exceeded the limitation of the water quality standards, and the overall pollution level was higher than the QURC.The PAHs concentrations of autumn surface soil samples ranged of 2001926 ng·L-1, with a mean of 577.5 ng·L-1, and for the spring samples, the range was 160.52040 ng·L-1, with a mean of 463.5 ng·L-1. The total concentrations of seven kinds of PAHs with carcinogenicity（∑PAHscarc） in fall soil samples rangeed of 84.7704.4 ng·L-1, with a mean of 255.9 ng·L-1, ranging of 92.2 700.9 ng·L-1with a mean of 245.7 ng·L-1 for the spring samples, the change rule was same to the ∑PAHs. The PAHs profiles were dominated by（5-6） rings PAHs in soil samples, accounting for 27.5%65.5% and 12.8%73.9% of the total PAHs contents in the autumn and spring soil samples respectively. The PAHs pollution level in surface soil was mainly for light pollution in QURC.2. Source apportionment of PAHs in LURC and QURC. The results showed that PAHs in the QURC mainly came from coil and biomass combustion, and some sources were fossil fuel combustion, which was in conformity with the energy structure. For the LURC, the PAHs in the waters mainly came from coil and biomass combustion, and the vehicles, coal and biomass combustion were the main sources of PAHs in soil, and another major source was petroleum combustion.3. Ecological risk assessment of PAHs in QURC and LURC. Based on risk quotient（RQ） method for ecological risk assessment of PAHs in waters, it was found that the PAHs concentrations were in light and moderate ecosystem risk in QURC, and were in moderate and heavy ecosystem risk in LURC. Based on RQ, Toxicity equivalent quality（TEQ）, ERL/ERM, TEL/PEL and mean ERM quotient methods for ecological risk assessment of PAHs in soils, it showed that the PAHs concentrations were mainly in low ecosystem risk, a little in moderate ecosystem risk in QURC, while in LURC, the ecological risk level in surface soil was moderate. |
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