Study On Assessment Of Polycyclic Aromatic Hydrocbarons Bioavailability In Soils

Polycyclic aromatic hydrocbarons are a unique class of pollutants which are constituted by hundreds of individual substances.These compunds contain two or more fused aromactic rings made up of carbon and hydrogen atoms.The behaviors and fates of PAHs are of increasing concern,on account of their non-degradation,persisence and carcinogenic,tumorigenic and mutagenic properties of certain of them.Assessing the availability of polycyclic aromatic hydrocbarons accurately and effectively in soil is important for risk assessments.Preliminary studies on the removal mechanism of polycyclic aromatic hydrocbarons in soil were made by laboratory simulation study;The toxicity for the soil contaminated by polycyclic aromatic hydrocbarons was evaluated by biological indicators,including earthworm,wheat and soil enzyme activity.Comparing of the different results of the indicators,the more sensitive indicators were choosen.Total polycyclic aromatic hydrocbarons content was determined by dichloromethane extraction.The bioavailability of polycyclic aromatic hydrocbarons was determined by hydroxypropyl-β-cyclodextrin.Large difference was observed between the two methods.The effects of aging on total PAHs content and bioavailability fraction were analyed.The main results are as follows:The removal pathway of polycyclic aromatic hydrocbarons in soil includes volatilization,biodegradation and abiotic degradation. Phenanthrene and pyrene in soil are based on microbial degradation, followed by abiotic degradation such as volatilization, chemical degradation. Microbial degradation and volatilization of phenanthrene are easier than pyrene. The amount of phenanthrene extracted by the means of HPCD was always higher than pyrene, so phenanthrene was more readily available than pyrene.Soil organic matter content and the nature of polycyclic aromatic hydrocbarons are the main influence factors .The paper chose a series of different indicators, including earthworm mortality, antioxidative enzyme activity, wheat seed germination, shoot length, root elongation, shoot fresh weight, and root fresh weight, antioxidant enzyme activity in root and shoot, soil enzyme activity. With the soil not aged, earthworm mortality, wheat seed germination, shoot length, root elongation, shoot fresh weight, root fresh weight were sensitive for the high concentration of contaminated soil (phenanthrene 200mg?kg-1 + pyrene 200mg?kg-1) ,but not for the low concentration of contaminated soil (phenanthrene 2mg ? kg-1 + pyrene 2mg ? kg-1).In order to accurately evaluated their toxicity,antioxidant enzyme activity in earthworms, roots and shoots of wheat( superoxide dismutase, catalase, malondialdehyde, protein) were measured. SOD is the most sensitive indicators, followed by CAT, MDA, protein content.With the soil aged for 30 days, earthworm mortality, wheat seed germination, shoot length, root elongation, shoot fresh weight, root fresh weight are no longer sensitive for high concentration (phenanthrene 200mg?kg-1+pyrene 200mg ?kg-1), antioxidant enzymes activity in earthworms, root and shoot of wheat were measured, SOD was the most sensitive indicator.Total PAHs content decreased as the time extended, and the rate was rather high at the initial stage, and then slowed down in the rest of time. The degree of decline in the phenanthrene than pyrene.Red soil had the highest concentration, yellow brown second, and black the lowest, proportional to the soil organic matter content soil.The amount of phenanthrene and pyrene extracted by the means of HPCD decreased as the time extended, and the rate was rather high at the initial stage, and then slowed down in the rest of time. The degrees of decline in the phenanthrene than pyrene.Red soil had the highest concentration, yellow brown second, and black the lowest. The total amount of phenanthrene and pyrene were significantly higher than the amount of phenanthrene and pyrene extracted by the means of HPCD. From the extraction efficiency point of view, red highest, yellow brown second, and black the lowest, and phenanthrene higher than pyrene. Therefore,we should select the appropriate extraction methods, so as to assess the risk accurately.