Distribution Of Polycyclic Aromatic Hydrocarbon(PAHs) In Farmland Of Parts Of Jiangsu Province And Its Ecological Risk

Persistent organic pollutants(POPs) have been of great concern due to their persistence in the environment,their bioaccumulation potential in the tissues of animals and humans through the food chain,and their toxic properties for human and wildlife.Polycyclic aromatic hydrocarbons(PAHs) are widespread contaminants in the environment.Some of the PAHs proved to be mutagenic,carcinogenic and teratogenic,and are listed as priority pollutants in the U.S.EPA.This study focuses on the contents,distribution,sources and ecological risk of 16 PAHs in soils of farmlands of parts of Jiangsu.The results acquired in this study will make us understand fate and risk of PAHs in soil.1.Contents and sources of 16 PAHs in soils of farmlands in parts of JiangsuContents of PAHs varied widely from 45.6～2286.8μg/kg in studied areas, averaging 1370.3 and 801.1μg/kg,respectively,for samples from Xinghua and Wujiang,signifying severe pollution,and 210.8 and 126.7μg/kg,respectively,for those from Yixing and Nanjing,meaning slight pollution or zero pollution.Based on the relative abundances of PAHs different in ring numbers,the ratios of Phe/Ant, Fla/Pyr and the finding of the site investigation,it was found that PAHs in the soils came from a number of sources,such as exhaust from automotives,combustion of coal,burning of straws and wood,leaking of petroleum,etc.2.Distribution characteristics of PAHs of soil profiles in farmlands and its affecting factorContents of PAHs of soil profiles in Yixing and Nanjing were determined. Concentration of total PAHs and every kind specie peaked at the soil surface and decline with depth,reducing rapidly in 0-30cm and keeping stability below 30cm of soils.Naphthalene and phenanthrene were detected from 0 to 80cm soil profiles, meaning high ability of transplant.Concentration of pyrene and benzo[a]pyrene was found lower than the limit of detection below the plough layer.Contents and characteristic of total organic carton(TOC),the physical and chemical features of PAHs,and human activity played major roles in affecting distribution of PAHs in soil profiles.3.Distrbution characteristic and the environmental significance of PAHs in particle size fractions of soils of farmlandTop soil of three types of paddy soils were studied and contents of PAHs of 16 species both in bulk samples and their particle size fractions were determined.The concentration of the total PAHs varies with the size of the particle fractions,which the order from higher level to lower is in those of＜2μm,200～2000μm,20～200μm and 2～20μm.Compared to that of bulk samples,PAHs are enriched either in the sand-sized or in the clay-sized fractions(with an enrichment ratio of 1.25-3.92) and depleted in the silt-sized fractions(with an enrichment ratio of 0.64-0.88).There is different environmental significance because of distrbution characteristic of PAHs in particle size fractions.Contents of PAHs in 200～2000μm can be distributed again and those in 2μm can be transplanted in soil-water and soil-atmosphere,then there exists environmental risk.There existed a general correlation of the total PAHs content with the contents of soil organic carbon,humus carbon and humis acid carbon respectively.The absorption and distribution of total PAHs in these different size fractions are mainly controlled by organic carbon content.4.The dynamic change of contents of phenanthrene in soils of farmlandThe laboratory incubation of one kind of paddy soils with different concentration of phenanthrene added to soil were studied and found that contents of phenanthrene decreased gradually.Degradation rate of phenanthrene accelerated with its concentration increasing.After incubation for 56d,contents of phenanthrene in paddy soil decreased quickly with 3.2 and 1.6μg/g concentration,the rate being 77.0%and 55.0%respectively,and degradation rate slowly with 0.8 and 0.4μg/g concentration being 48.3%and 25.0%respectively.The reason is that the more contents of phenanthrene added to soil,the more contents biodegraded and absorbed by paddy soil. 5.The effect of phenanthrene in soils of farmland on enzyme activity and microbial diversityThe dynamic changes of soil enzyme activities were researched with incubation experiment under condition of phenanthrene was added to soil.The relationship between enzyme activities and different phenanthrene concentrations were studied. The results showed that there is influence of phenanthrene in soil on urase and phosphotase.Compared to CK,urease activity was inhibited within 7 day under condition of phenanthrene concentration＞3.2μg/g.However,the activity of phosphatase was activated by phenanthrene from 1day to 28 days under condition of phenanthrene concentration＞1.6μg/g.There is no significant change of catalase activity in the phenanthrene with range of 0.4 to 3.2μg/g in the period of 56 day.It was concluded that soil urease activity and phosphatase activity may be considered as diagnoses indicators of soil contamination with phenanthrene,and the most sensitive period of the diagnoses was from the first day to the seventh day after phenanthrene contamination.Phosphotase activity is more sensitive.Molecular technique of PCR-DGGE on different types of paddy soils with different contents of phenanthrene(0.05～1.60μg/g) was used to study microbial gene diversity.The results indicated that microbial gene diversity did not change under condition of phenanthrene concentration≤1.60μg/g.However,there existed special gene diversity which can degrade phenanthrene in polluted soils.