| In recent years,with the improvement of people’s living standard,we gradually begin to pay attention to the environment that we live in.The state council also formulated 10 measures to control soil pollution in May 2016,aiming to improve soil quality and stabilize the ecosystem comprehensively.The hexachlorocyclohexanes(HCHs)and dichlorodiphenyltrichloroethanes(DDTs)are the main components of organic pollutants in soil and surface water.Since HCHs and DDTs were synthesized in the 1940 s,they have been used worldwide to kill insects and disinfectants.Because organochlorine pesticides are difficult to degrade,they are also toxic that can be transmitted globally.HCHs and DDTs have a subtle influence on people’s health and environment.There is no specific study on HCHs and DDTs in surface water-soil system in Xi’an.So the analysis of HCHs and DDTs in surface water-soil system in xi’an was studied in this paper,and the main contents of the dissertation are as follows:(1)The brief introduction,research progress both at domestic and overseas of persistent organic pollutants,pretreatment and determination method of organochlorine pesticides were discussed in the review section systematically.The significance and main contents of this thesis were presented.(2)Analysis and detection of HCHs and DDTs in surface water samples.Automated SPE extraction conditions were optimized.Sample injection rate with 8 m L/min,the elution solvent with acetone/hexane(1:9,V:V)and the elution volume with 6 m L are as the best condition of solid phase extraction,Analysis method of organochlorine pesticides were established with GC-MS.The recovery was in the range of 96.50%-109.3%,relative standard deviation(RSD%)was in the range of 1.2%-8.7%,that can be accurately used for the analysis of HCHs and DDTs in surface water.(3)Analysis and detection of HCHs and DDTs in soil.The conditions for accelerated solvent extraction were optimized.The extraction solvent with acetone/n-hexane(5:1,V:V),extraction temperature at 100 o C,static cycle 3 times and static extraction with 5 min were determined as optimum extraction conditions.At the same time,the purification method was optimized,the elution solvent with acetone/hexane(1:9,V:V)and the eluenting volume with 6 m L were established as the optimal solid phase extraction condition.The detection method of eight kinds of organochlorine pesticides were established with GC(μECD).The recovery was in the range of 94.30%-119.2%,RSD% was in range of 3.5%-9.4%,method detection limit was in the range of 0.03-0.08 μg/kg,that can be accurately used for the analysis of HCHs and DDTs in soil.(4)Samples were collected from the surface water that state controlled and the surrounding farmland soil of Xi’an city.In the surface water samples,the total concentrations of HCHs and DDTs were in the range of ND-28.36 ng/L and ND-37.34 ng/L,respectively.In the soil samples,the total concentrations of HCHs and DDTs were in the range of 0.65-16.49 μg/kg and 1.04-17.50 μg/kg,respectively.The total concentrations of HCHs and DDTs in summer were a little more than that in winter both in surface water and soil samples.Because there is more rain in the summer,the scouring of rainwater on the soil and abundant sunshine resulted in higher levels in summer.It was proved that many factors can affect the distribution of organochlorine pesticides,for example,changes in soil pollutants before and after crop planting an so on.The experimental results showed that HCHs in surface water and soil of Xi’an city were both derived from the historical residues of pesticides and lindane.DDTs were both derived from the historical residues of pesticides. |
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