Occurrence of polycyclic aromatic hydrocarbon (PAH) in soils around two typical lakes in the western Tian Shan Mountains (Kyrgyzstan, Central Asia): Local burden or global distillation?

The United Nations Educational, Scientific and Cultural Organization (UNESCO) world natural heritage Tian Shan Mountains, situated in Central Asia, have experienced a dramatic increase in polycyclic aromatic hydrocarbon (PAH) contamination, not only because of increasing volumes of tourism-derived traffic but also because of the atmospheric transport of polluted westerly winds under global distillation effect. To assess the significance of two possible sources of PAHs, 16 priority PAHs were determined in 39 soil samples collected in August 2013 around Lake Issyk-Kul (YKR, 1606 m) and Lake Son-Kul (SKR, 3010 m) as typical mountain lakes in the western Tian Shan Mountains. Total PAH concentrations ranged from 52 ng/g dw to 9439 ng/g dw. The highest PAH levels were found in the industrial and urban areas of the YKR ( > 1000 ng/g dw); however higher levels were in the agricultural and rural areas of two regions (300-1000 ng/g dw), both dominated by 4-,5-ringed PAHs. In contrast, the lowest PAH levels ( < 200 ng/g dw) were mostly distributed in the pristine areas, dominated by 3-,4-ringed PAHs. Diagnostic ratio and Positive Matrix Factorization model infer that high PAH levels were mainly generated by petroleum combustion derived from local burgeoning tourism traffic beside road construction, indicated by simultaneously measured n-alkanes features (low carbon preference index and pristane/phytane ratio close to 1 with high unresolved complex mixture values). On the contrary, low PAH levels primarily from biomass combustion with unburned petroleum processes are ascribed to exogenous atmospheric transport under global distillation effect, because n-alkane sources here are biogenic input without petroleum contamination. An altitudinal/temperature dependence of 2-,3- and 4-ringed PAHs was significant in the SKR, and the soils in the SKR serve as a sink for PAHs in global cycling.