Migration Regularity Of PAHs In Soil And Its Effect On Plant Growth

Polycyclic Aromatic Hydrocarbons(PAHs)is a kind of refractory dangerous organisms generally existing in environment. It draws a wide attention among many national governments and scientific research field because of its carcinogenicity, teratogenicity and mutagenicity. There exists a certain content of Polycyclic Aromatic Hydrocarbons no matter in atmosphere,water or the soil,and the number of PAHs is increasing as time goes on. PAHs can pose a serious threat to the environment and human’s health in various ways. So the study on the migration regularity of PAHs in the soil and its impact on the growth of plants, has both theoretical and practical significance to further understand the repair mechanism of plants to soil and the safety in production of agricultural products. Regarding Chinese cabbage and wheat as representative crops,and regarding the three typical PAHs,including naphthalene,phenanthrene and pyrene,as the representative pollutants,this paper systematically discusses the migration behavior of PAHs in the soil and the interaction between plants and PAHs in the soil. The main research results are as follows:1. This article used naphthalene,phenanthrene and pyrene as the representative of pollutants,analyzed their changing behavior and compared the characteristics of these three pollutants in the soil over time. The results show that with the passage of time,the residual concentrations of these three pollutants in the soil are dropping,and with the increasing number of PAHs’ s benzene ring,the residual concentrations finally present a trend of naphthalene< phenanthrene< pyrene. There are some main ways of removing PAHs in the soil,such as volatilization,photodecomposition,microbial degradation and other loss. Microbial degradation and other ways of loss play a dominant role among these ways,achieving about 50%. The loss arose from volatilization and photodecomposition is less than 10%. And it’s easier for naphthalene and phenanthrene than pyrene to volatize,photodegrade and microbial degrade.2. By using wheats as experimental plants,this paper studied the impact of plants on migration of naphthalene,phenanthrene and pyrene in the soil-plant system and their residual behavior. The results show that the existence of the plants have a promoting effect on reducing the low ring PAHs in the soil. After 30 days, the residual concentrations of naphthalene,phenanthrene and pyrene of the experimental groups which grow wheats in the soil are lower than the control groups without plants by an average of 9.75%,8.77%,9.96%,and lower than the control groups which is sterilized and no plants by 8.88%,16.1%,16.14%. We used Chinese cabbages as experimental plants,studied the accumulated method of PAHs which were absorbed into the plant from soil. The results show that Chinese cabbages have a certain enrichment capacity on low rings PAHs in the soil. And the accumulation of naphthalene,phenanthrene,pyrene in the overground part of plants is much larger than in the underground part.3. This paper used Chinese cabbages and wheats as experimental plants,studied the impact caused by PAHs of the different starting pollution concentrations in the soil on the growth of plants. The results indicate that the polycyclic aromatic hydrocarbons, as naphthalene,phenanthrene and pyrene,have an obvious inhibitory effect on the germination and growth of Chinese cabbages. The germination rate and biomass of Chinese cabbages in the polluted soil are significantly lower than control groups without pollutants,and its germination rate and biomass decrease significantly with the increasing concentration of pollutants. However,it’s different for wheats. When the average pollutant concentration is 0~100 mg/kg,PAHs have a promoting effect on the germination of wheat. When the average pollutant concentration is more than 100 mg/kg, PAHs have a inhibiting effect. With the increasing concentrations of phenanthrene and pyrene,the activities of PPO and POD in the roots,stems and leaves of Chinese cabbage are rising at first and then reducing. Either in the soil processing by phenanthrene or pyrene,the PPO and POD activities in the roots of Chinese cabbages is greater than the stems and leaves of them.