Study On Migration And Transformation Characteristics Of OCPs And PAHs In Epikarst System

As one of important drinking water resources of local people in the karst mountain areas, epikarst springs have been an important and new aspect of geological survey in Southwest China. There is an important practical application for exploiting and utilizing epikarst springs to resolve the difficulty of water supply to sparsely dispersed residents and their livestock and to resolve the problem of irrigation for some scattered farms in karst mountain areas. However, epikarst springs are facing the threats of water quality deterioration due to the fragility of karst environment and the disturbance of human activities. But the studies on organic pollutants in epikarst spring are very limited. So it is necessary to study the distribution, the character of composition, source, migration and transformation of organic pollutants and effect of anthropologied activity on epikarst spring. So the thesis aimed at the four epikarst spring in Nanchuan, to study the character of migration and transformation of PAHs and OCPs in epikarst system and the character of temporal and spatial distribution of PAHs and OCPs in epikarst spring water.The concentration of OCPs in typical karst area soils ranged from16.48to731.74ng/g, the mean value was253.57ng/g. The detection ratios of OCPs in karst soils were100%, but the concentration of different kinds of OCPs varied greatly. HCHs, DDTs, methoxychlor and mirex were the most dominant compounds among the24OCPs. The concentration of PAHs ranged from439.19to3329.72ng/g, the mean value was1271.49ng/g, and the detection ratios of16PAHs were100%. The concentration of PAHs in HG soils was biggest, and the concentration of PAHs in BSW soils was smallest. The PAH constituents were affected by altitude. With the increase of altitude, the percent of low molecular weight PAHs increased, but the percent of high molecular weight PAHs decreased. The isomer pair ratios of HCHs indicated HCHs in epikarst soil originated from the residues of historical application of technical HCHs and lindane, and under the influence of environment, the compositions of HCH isomer changed greatly. DDTs in soils of BSW and SF soils came from the use of technical DDT and dicofol, and the use of technical DDT might be responsible for the freshly DDT input in HG spring and LH soils, but not the dicofol type DDT. Integrated principal component analysis and isomer pair ratios suggested the PAHs in epikarst soils were derived from high temperature combustion of coal, biomass and oil, partially from coking product.In comparison with soil quality standards of China and the Netherlands, the concentration of DDTs in BSW soil was near to the reference value of unpolluted soil according to soil protection guideline of the Netherlands, and the levels of DDTs in LH and HG soil were classified as low pollution, while the SF soil can be classed as no pollution. According to Maliszewska-Kordybach standards of PAHs concentration in soils, the soils in HG spring watershed and SF spring watershed and the LH dry land were categorized as heavy pollution, LH rice land and forest land were classified as pollution, and the soils in BSW spring watershed were classed as light pollution. But according the TEQcare values of16PAHs and7carcinogenic PAHs, the level of PAHs contamination in HG spring soils was highest, and the contamination level of SF epikarst spring soils were lowest. So when evaluating the contamination levels of soil PAHs, the16PAHs concentration,7carcinogenic PAHs concentration and the TEQcare values should be taken into account.The analytical results of soil profiles in study area, the detection ratios of OCPs and PAHs were100%. The OCPs concentration in soil profiles ranged from5.74to974.10ng/g, the mean value was88.78ng/g, and the PAHs concentration in soil profiles ranged from161.09to3284.71ng/g, the mean value was986.78ng/g. In HG, LH and LR soil profiles, OCPs accumulated in0-30cm soil layer. And below30cm layer, the concentration of OCPs changed lightly. But in SF and BSW soil profiles, the concentrations of OCPs were homogenized in whole profile. The land use patterns effected the vertical distribution of PAHs concentration. In the same land use patterns, the vertical distribution profiles of PAHs concentration were similar. In LH and BSW soil profiles, the biggest concentrations of PAHs were in0-2cm soil layer, and the biggest concentration of PAHs in HG and LR profile were in10cm soil layer, while in SF soil profile, the biggest concentration of PAHs was in40cm soil layer. In HG, LH and BSW spring watersheds, the velocity of importing to surface soils were faster than the velocity of PAHs transporting to deep soil layer, but in SF spring watershed, the velocity of importing to surface soils was smaller than the velocity of transporting to deeper soil layer.In different soil profiles, the compositions of HCHs and DDTs had large difference. In SF, LR and BSW profiles, y-HCH was the main component of HCHs, and p,p'-DDD was the main component of DDTs, but in HG and LH profiles,(β+δ)-HCH was the main component of HCHs, and p,p'-DDT was the main component of DDTs. To PAHs composition, the composition of PAHs in LR and SF profiles were mainly low molecular weight PAHs(LMW PAHs), and in HG profile, the composition of PAHs was mainly high molecular weight PAHs(HMW PAHs), while in LH and LR profiles, the PAHs compositions in0-2cm soil layer were mainly HMW PAHs, and the compositions of PAHs below0-2cm soil layer were mainly LMW PAHs.The sequence of the migration capabilities of OCPs in different soil profiles from strong to weak was SF>BSW>LH>LR>HG. In different OCPs component, the migration capability of endosulfan was strongest, the migration capability of ALDs was in the second place, the migration capabilities of DDTs and methoxychlor was weakest. In different soil profiles, the migration capabilities of HCHs, CHLs and HCB were different. The migration capabilities of PAHs in different soil profiles had a large difference. In general, PAHs with less rings were easier to migrate than the PAHs with more rings. Multiple regression analysis between the total OCPs and the physicochemical properties of soils showed that there were three factors impacting the total OCPs in LR profile, the three facters were the total organic carbon(TOC)content, water content and pH values respectively, there were two factors in BSW soil profile, they were TOC and water content, and TOC was only one factor in HG and LH soil profiles, but there were no factors impacting the total OCPs in SF profile. And multiple regression analysis between the total OCPs and the physicochemical properties of soils showed that TOC was the common factor impacting the total PAHs content in HG, LH, LR and BSW soil profiles, and there were no factors impacting the total PAHs content in SF profiles.The detection ratios of24OCPs in BSW and LH spring water were100%. Except for p,p'-DDE in HG spring water and in SF spring water, the other23OCPs were all detected. The detection ratios of16PAHs in four springs were100%. The concentrations of OCPs in HG, BSW, and LH spring in rain season were higher than that in dry season, but in SF spring, the concentration of OCPs in rain season was lower than that in dry season. And the concentration of PAH in four springs in rain season were all higher than that in dry season, but the variation tendency of the concentration of16PAHs in different spring had a large difference.The compositions of OCPs in SF, HG, and LH spring water in different month were close, but the composition of OCPs in BSW spring in different changed greatly. In four springs, other OCPs was the main component of OCPs, and the proportion of HCHs and DDTs varied greatly. And in four springs, the compositions of PAHs were mainly (2+3)rings PAHs. In SF, HG and LH spring, season variation had great effect on the composition of PAHs, but in BSW spring, season variation had little effect on the composition of PAHs.The ratios of α/γHCH showed that HCHs degraded during the process of migration in the HG, BSW and SF epikarst spring system, and the degradation of γ-HCH was most obvious in the four isomers of HCHs, but in LH epikarst spring system the degradation of HCHs was not obvious. The ratios of Ant/(Ant+Phe) and Fla/(Fla+Pyr) changing with season showed that Ant, Phe, Fla and Pyr were easy to migrate in epikarst system. As compared with the ratios of Ant/(Ant+Phe), BaA/(BaA+Chry) and InP/(InP+BgP), the ratio of Fla/(Fla+Pyr) was more sensitive to reflect the information of source.The concentration of OCPs in four springs did not exceed the limit of standard for drinking water quality in China, USA and World Health Organization. That showed that the OCPs pollution was not severe in epikarst spring and had little ecological risk. But during one year observation, the total PAHs concentration in several month water sample exceed the limit of standard for drinking water quality in China, and the concentrations of Bap were far beyond the limit of drinking water quality in China, the limit of underwater quality in Netherllands and the water quality in Canada. These showed that the epikarst spring water suffer severely pollution of PAHs.A dynamicfugacity model which divides the soil into multiple soil layers has been developed and used to simulate the temporal trends of the concentration, the transfer and fate of γ-HCH in HG springwatershedduring1952-2020.Comparisons between the calculated and measured concentrations of γ-HCH in soil profile show good agreement, that suggest the dynamic fugacity model which divides the soil into multiple soil layers is appropriate to simulate the transfer and degradation processes of oranic polluants in karst area multimedia environment. During1952-1983, the dominant input source of γ-HCH is technical HCHs through agricultural application, and the amount of γ-HCH added up to183kg. The average input and output amount of γ-HCH through air advection were69.86kg and70.37kg. And the amount through degradation of γ-HCH added up to5325g. In1983, there were approximately4607g γ-HCH in all environmental compartments of the study area and99.88%of which existed in soil compartment. After1984, air advection became the dominant input sources of γ-HCHwhen the application of technical HCHs was prohibited, the concentration of γ-HCH in air, plants and0-20cm layer soil descended quickly. The concentration of γ-HCH in soil layers below0-20cm soil layer increased until1993. The amount of γ-HCH remaining in the study area environment is18g in2020by prediction, is0.4%that in1983.During1952-1983, the amount of γ-HCHtransferred into epikarst spring water added up to141g, but during1984-2020, the amount added up to591g. According to the calculation of model, the dominat transfer processes of γ-HCH in the study area are the process transfer from0-20cm layer to the next layer and the exchange between air and plants.