Altitudinal Gradient Distribution And Source Path Analysis Of PAHs In Soil Of Jinfo Mountain, Chongqing

Polycyclic aromatic hydrocarbons (PAHs) are a kind of persistent organic pollutants (POPs), with higher toxicity and bioaccumulation. They are semi-volatile compounds, and difficult to degrade. They can undergo long-range atmospheric transport on a global scale because of the long half-life. The "global distillation" and "the grasshopper jumping effect" are generated with the temperature and latitude. And each component of PAHs differentiates in the transmission processes.The alpine karst area has the characteristics of lower temperature, slope winds, higher precipitation, and high dry and wet deposition. And it’s a rendezvous for organic pollutants, which can receive the atmospheric pollutants from long-distance transmission like high latitudes, and will affect the ecological environment. With a special hydrogeological structure, karst area is unable to act as filters to prevent contaminants from reaching surface waters, and the surface water and groundwater are closely linked. The pollutants from atmospheric dry and wet deposition can leakage quickly under the action of highly hydraulic conductivity. The alpine karst water system serves as a water supply for the lower area, so the pollutant will also affect the lake water, groundwater and snow in alpine karst area.Based on the Jinfo Mountain karst area of Chongqing as the research object, this paper aims at studying the altitudinal gradient distribution and influence factors of PAHs in soil of Jinfo Mountain, and provides a basis for the protection of human living environment, mountain resources, terrestrial and aquatic ecosystems. Through analyzing composition of PAHs in soil around four pollution sources in the Nanchuan district, the author gets PAHs composition spectrum from different sources, and compares with composition spectrum of PAHs in Jinfo Mountain. And the author also analyzes source path of PAHs in Jinfo Mountain, in order to provide the basis for the control of pollution. Results show that:1. The content of PAHs in the surface soil of spring was higher than the content of autumn at Jinfo Mountain. Because the sampling time was in early spring and early fall, the essence of the content of PAHs in soil was a representation after a winter and summer. The increased amount of winter heating coal increase atmospheric emissions of PAHs, and low temperature was against to volatilize of PAHs from the surface to the atmosphere, causing the spring stored the higher concentration of PAHs in the surface soil. The high temperature of summer was beneficial to PAHs to evaporate into the atmosphere from the soil, the stronger solar radiation result in photolysis of PAHs; With the increase of rainfall in the rainy season, surface runoff and leaching effect would make the PAHs in the surface soil be taken away, so the PAHs content was lower in the autumn. As the "temperature difference effect", the summer was more conducive to the transmission and settlement of PAHs, but the low-ring PAHs were degraded during transmission because of the strong light in summer. Meanwhile, the low-ring PAHs with a higher water solubility relative to the high-ring PAHs, were easily migrated with a lot of rain, resulting in a relatively low total content of PAHs in the north slope and the south slope in autumn and a higher content of high-ring PAHs than spring. West slope didn’t exhibit this phenomenon, probably because the presence of local PAHs combustion sources in the winter and spring. The content of PAHs in soil of spring showed:north slope>west slope≈south slope, the large gap of PAHs content between south slope and two other slope was closely related to the prevailing wind direction in the study area. The content of PAHs from each slope was near, because of the high temperature, strong radiation, the degradation and volatilization of PAHs played an important role.The range of TOC content was from 1.39% to 24.22%, and the mean value was 6.46%. The PAHs content in soil of north slope had a weak correlation with soil TOC, while the south slope and west slope showed a significant correlation. The high-ring PAHs had a stronger correlation with soil TOC than low-ring PAHs.TOC was an important factor that affected the content of PAHs, but the PAHs content in soil of mountain may be affected by other factors such as human activities, soil microbes, temperature and altitude.2. The content of PAHs in the autumn soil of three slope showing an increasing trend with the increase of elevation. Due to the impact of "temperature difference effect", the summer was beneficial to the transmission of PAHs, and the alpine "condensation effect" was obvious. The content of PAHs in spring soil of the south slope had progressively increased with the change of altitude influenced by the prevailing wind. Overall, along with the variation trend of altitude, the change of the content of carcinogenic PAHs was consistent with the total content of PAHs, which showed that mountain areas were beneficial to the accumulation of PAHs, and the natural environment were more susceptible to the impact of pollutants. The ratio of different-ring PAHs in gross PAHs showed no regularity with the rise of altitude. The combustion activities of local residents and the emissions of tourist car were a part of the source of PAHs. In the soil from the south slope and soil from the west slope in autumn, various-ring PAHs was increased by the rise of altitude. The increase of low-ring was most obvious, and the volatility of high-ring was relatively high. The results related to the properties of PAHs, and low molecular weight PAHs exist in the atmosphere in gaseous form, more easily transport with the atmospheric; but the high molecular weight PAHs tend to adsorb onto the surface of atmospheric particulates, and spontaneously settle at lower altitudes.The PAHs in the soil of the research area mainly came from the combustion sources of coal and biomass, petroleum and combustion of petroleum products. Atmospheric deposition was the main contributor, followed by combustion activities of local residents and vehicle emissions. In the research area, the soil and water have been polluted to a certain extent, but the toxicity risk was relatively low.3. By comparing the pollution source and composition of PAHs in the study area, this research analyzed the source path of PAHs in Jinfo Mountain. In the research area, the PAHs in soil from the north slope and south slope mainly came from the Atmospheric transmission of four factories emissions, and coking plant emissions of PAHs represents a significant share. The whole south slope polluted by automobile exhaust, and might have combustion sources of coal at high altitudes, while the north slope is at middle altitudes.The PAHs in the environmental media of the Shuifang Spring watershed was mainly from the atmospheric transmission of urban pollution sources, followed by a small amount of automobile exhaust.