[Contamination of polycyclic aromatic hydrocarbons in surface water in underground river of Dashiwei Tiankeng group in karst area, Guangxi].

In order to understand the composition, sources and contamination characteristics of PAHs in water from underground river of Dashiwei Tiankeng group in typical karst area located in Leye County, Guangxi. The water samples were collected from different sections to analyze 16 priority polycyclic aromatic hydrocarbons using GC-MS. The results showed that concentration of Sigma PAHs (the total PAHs) in water ranges from 54.7 ng/L to 192.0 ng/L, with an average concentration of 102.3 ng/L. The predominant PAHs in water are 2-3 ring PAHs, accounting for 65.1% of PAHs. The distribution of PAHs in water sampled along the underground river indicates that the mean concentration of PAHs in upstream area is higher than that of downstream because of wastewater discharge. Meanwhile, the underground river has some adsorption effect to 4-6 ring PAHs. The concentration of Sigma PAHs at Dashiwei Tiankeng section increases 93.8% attribute to the release of PAHs coming from Karst environmental medium and/or atmospheric transmission in underground river system. However, the concentration of Sigma PAHs at the confluence section of the tributary of Dashiwei Tiankeng is 47.3% less than that of the first upstream section duo to dilution. The concentration of Sigma PAHs at Bailang outlet section is 128.3% and 17.8% higher than that of flow-in section and Dashiwei Tiankeng section respectively. The ratios of specific PAHs indicate that the PAH sources in Leye County and Dashiwei Tiankeng areas mainly come from both petroleum and its combustion. However, the petroleum origin comes from anthropogenic inputs in town and the natural inputs in Dashiwei Tiankeng. The PAH sources in rural areas are mainly originating from the combustion of grass, wood and coal. Comparison to other areas in the world, the Sigma PAHs residual levels in underground river water in Dashiwei Tiankeng group is at the low level. In six sections, concentrations of benzo[a]pyrene (BaP) in surface water exceed the state quality standards.