Variation Characteristics And Influence Factors Of Polycyclic Aromatic Hydrocarbons In Karst Subterranean River During Rainfall Events

Polycyclic aromatic hydrocarbons(PAHs) are a byproduct of incomplete combustion or pyrolysis of organic compounds, which are widely distributed in water and air. PAHs in the water are mainly through surface runoff, atmospheric dry and wet deposition, soil(sediment)-water, gas-water interface exchange and so on; PAHs are important component of the atmospheric particulate matter, mainly exist in the gaseous and particulate for m in the atmosphere. Researches show that rainfall can greatly reduce the concentration of PAHs in the atmosphere, leach of atmospheric particles directly and rapidly. Rainfall is also an important factor in environmental pollutants migration and redistribution, also the pollutants accumulated in the surface can be washed by the runoff, and eventually received to waters.The karst subterranean water is an important drinking water in the southwest of China, compared with non-karst areas, the karst area is easy to be polluted, because the soil layer in the karst areas is thin and discontinuous distribution, in addition, developed a large number of karst forms, such as the water tunnel, the funnel, the vertical shaft and the crack. Because of the special surface and subsurface structure of the karst area, the subterranean water is sensitive to the rainfall. The rainfall can accelerate the transformation between the rain water, surface water and subterranean water. The study of the response of subterranean water to rainfall in karst area is mainly focused on the response of hydrology and geochemistry to rainfall, but little research on PAHs. Therefore, it is necessary to study the transfer process of PAHs in the subterranean river system during the rainfall event.This study is based on the Nanshan laolongdong subterranean river which located at Chongqing, measured by GC/MC or GC/MS, the karst subterranean river and its surface pollution as the main line of the study. The purpose is study the spatial temporal chan ges of PAHs of Nanshan laolongdong subterranean water, discuss variation characteristics and influence factors of PAHs in karst subterranean river during rainfall events. The results as below:1. The content of PAHs: The detection rate of low ring in disso lved PAHs is high, and the difference of time and space is large, laolongdong dissolved PAHs is the largest, the mean value is 434 ng·L-1,the reason may be affected by the environmental impact of the sampling site; The mean value of laolongdong particulate PAHs is 379 ng·L-1,monomer compound Flu changes greatly, the particulate PAHs seasonal variations. From the structure of PAHs: the dissolved PAHs compositional profiles are dominated by 2, 3 ring compounds, which accounted for 85.07 % of the total concentrations of PAHs, followed by the 4 ring, 10.36 % of the total, the 5,6 ring is only 4.57 % of the total. The particulate PAHs compositional profiles are dominated by 2, 3 ring compounds, which accounted for 45.93 % of the total concentrations of PAHs, followed by the 5, 6 ring 35.10 % of the total, the 4 ring is only 18.97% of the total. From the point of view of PAHs pollution levels, the water polluted by Phe, Fla. Dissolved PAHs most of the light to moderate pollution, only a very small number to reach the level of heavy pollution.2. Laolongdong subterranean river responses to rainfall rapidly, karst hydrological system belongs to the pipeline and fissure combination. During the heavy rainfall: rainfall has a great influence on the dissolved PAHs, the content fo dissolved PAHs range from 101 to 3624 ng·L-1, the content of particulate PAHs range from 151 to 1321 ng·L-1; Dissolved PAHs is mainly composed of 2, 3 ring, followed by the 4 ring, the 5, 6 ring content is the lowest; Particulate PAHs is mainly composed of 5, 6 ring, followed by the 2,3 ring, the 4 ring content is the lowest, heavy rain can bring more 5,6 ring PAHs. During the weak rainfall: the dissolved PAHs content is relatively stable, the content of dissolved PAHs range from 220 to 440 ng·L-1, the content of particulate PAHs range from 144 to 1051 ng·L-1; Dissolved PAHs is mainly composed of 2, 3 ring, followed by the 5, 6 ring, the 4 ring content is the lowest; Particulate PAHs is mainly composed of 5, 6 ring, followed by the 2, 3 ring, the 4 ring content is the lowest. The composition structure tendency of the dissolved PAHs during rainfall is that 2, 3 ring increase at the beginning of rainfall, and with only 2, 3 ring phenomenon, followed by a small amount of 4 ring, with sustained 5, 6 ring detection is increasing gradually, At this time, the dissolved PAHs in water is mainly with the 4, 5, 6 ring, but the duration is short, and then the proportion of 4, 5, 6 ring is reduced, and then the dissolved PAHs is mainly composed by 2, 3 ring.3. Rainwater bring pollutants which exist in the air into the subterranean river system, furthermore the pollutants which accumulated in surface get into the pipeline by runoff, and eventually enter the subterranean water; Meanwhile, sediment resuspension, infiltration of soil contaminants also have effect on the PAHs; The PAHs in water mainly originated from the incomplete combustion of petroleum products and fossil fuels, combustion of coal.