Concentration, distribution and sources of polyaromatic hydrocarbons in soils from the Karst tiankengs, South China

Polycyclic aromatic hydrocarbons (PAHs) were investigated in the surface soils from Dashiwei and Datuo Karst tiankengs, Guangxi Province, South China. Concentrations of total PAHs ranged from 16.93 ng g(-1) to 190 ng g(-1) with a mean of 58.29 ng g(-1). In Dashiwei more PAHs were concentrated than in Datuo (mean 74.42 ng g(-1) > 42.15 ng g(-1)). Dashiwei and Datuo accounted for the majority of all PAHs concentrated in the lower location through increased rates (58% and 37%) from the upper to lower geographical levels, respectively. Dashiwei presented the stronger trapping ability for heavier molecular weights on the tiankeng floor with a concentration increase rate of 167% when compared to that of the lighter molecular weights (which had a concentration increase of rate 6%), which was in contrast to the Datuo with a concentration increase rate of 37% for lighter molecular weights and 31% for heavier molecular weights. In Dashiwei, it was found that the ratio of heavier PAH compound molecular weight resulted in its higher precipitation recording on the tiankeng floor. The differentia between two tiankengs, therefore, are related to their environmental characteristics and the PAHs physiochemical properties. The analytical result from the PAHs indicators suggest that a petrogenic source was dominant in the area studied. Therefore, the karst tiankeng has the potential to act as a geophysical well for PAHs deposition, especially for the heavier molecular weighted PAH.