Study On The Characteristics Of The Adsorption Of BHC And DDT To Typical Farmland Soil

Organochlorine pesticides have seriously contaminated the ecological environment due to its long remnant and stability. It has reported that BHC and DDT can endanger the human health even its concentration is low in water by accumulated through animals and plants or transported by food chains. Our country has banned its production and use in early 80years last century. But restricted by kinds of environment conditions, the degradation speed is very slow. In the environment superintend reports of some area proved that the residue of BHC still can be detected even in high concentration, and it is confirmed that one of those widely used POPs.Organochlorine pesticide residue has latent danger to the agricultural environment, agricultural products and also the human health. With the development of society and increasing population, people are up against serious damage of biosphere, the lack of resource, increasing serious pollution, including the soil and groundwater pollution. Soil is not only the carrier but also the decontamination ground of pollutants. Adsorption and desorption processes have received considerable attention as one of the most important processes affecting the mobility, degradation and biological activity of adsorption/desorption of organic pollutants in soil.The current study on the characteristics of transport and transformation of organochlorine pesticides in soil and groundwater environment mostly focuses on surface soil, unsaturated soil (vadose zone) and saturated zone soil. But much of them are limited in some segment of the migration and transformation progress as static characteristics or dynamic ones of fluoride migration. Simulation experiments with comprehensive consideration of each segment are rare.Based on the previous experimental studies, laboratory experiments in this thesis were processed to investigate the adsorption of organochlorine pesticides in the soil of Shenyang Liuwangtun and Shenyang Zhangyizhan and the effects of pH on adsorption. The migration and transformation of organochlorine pesticides were also analyzed by using the adsorption partition coefficient of pesticides and adsorption isotherms according to physical chemistry and absorption results. It will be helpful to understand the characteristics and affecting factors of the migration and transformation of organochlorine pesticides in the unsaturated soil and contributive to supply reference to study soil restoration and groundwater pollution mechanism. It is necessary to make full use of groundwater which is the main source of agricultural water and domestic water to reduce the serious shortage of water resource.To detect trace BHC and DDT in water with solid phase extraction-gas chromatography using cyclohexane to be the desorption solvent. The pre-treatment of water sample was studied. This method's detection limit was low, and it is also accurate with good recovery.At the stage of adsorption thermodynamic experiment, equilibrium solution concentration decreased and the corresponding amount of adsorption of BHC and DDT increased gradually with the rise of the adsorbent content, while unit adsorption quantity showed the opposite trend, it means that the lower adsorbent concentration, the higher adsorptive capacity within a given range will appear. Several reports have found the adsorption of organopesticide in soil is affected by pH of soil solution, usually with the increase of pH, the adsorption capacities of organopesticide increased. And this paper reveals that with the pH of soil solution increasing, the BHC unit adsorption in L soil decreased firstly and then increased; while that in Z soil was changeless after increasing and then decreasing. BHC adsorption amount by L soil was a little bigger than BHC adsorption amount by Z soil with the same pH.The values of the correlation coefficient (R) showed that the experiment data followed Langmuir adsorption dynamics isotherms. BHC or DDT adsorption amount with time was increased on the whole. The adsorption to soil was composed of two stages, namely rapid reaction stage and slow reaction stage. At two initial BHC or DDT concentration, a contact time of 4-8h was sufficient to achieve equilibrium. Adsorption amount of BHC or DDT within 2h reached about ninety percent. In addition, adsorption and desorption occur simultaneously during the process of adsorption (desorption) of organics. Two compartment models were used to describe the reversible process, and the values of the correlation coefficient (R) coincide well with the experiments. Characteristics of BHC migration and transformation in different types of soils of water logged aeration zone have been studied through laboratory soil-column experiments. The migration velocity of BHC was slow and the pollutant concentration from the leach in effluent is small in I column(0~20cm), II column (20~40cm)and III column (40~60cm)which were filled with the layers from 0 to 100 cm in depth in Z soil; while it was longer than 200 hours to show significant change of leaching concentration in IV column(60~80cm) and then the concentration increased slowly. The migration speed of BHC increased obviously in V column (80~100cm). With the increase of time, the leaching concentration increased and reached a maximum, and then there was no remarkable change of BHC in V column.The results obtained from leaching curves showed that the migration speed of BHC in five soil columns was: V> IV >> I, II, III. The possible reason was that the organic matter content of V column was higher than the other four soil columns. Previous studies have shown that the adsorption capacity of soils for BHC is stronger with higher organic matter content Therefore the adsorption capacity of BHC to V soil column was the lowest, thus the migration speed of that was higher. That's to say, once organochlorine pesticides polluted water have arrested in subsoil of vadose zone, the migration and release of pollutants in soils possessed potential risks to underground water and ecosystem. It has important meanings to know and research the characteristics of the migration and transformation of organochlorine pesticides in different soil horizons, and it also provides the theoretical foundation for the prevention and remediation of soil and groundwater pollution.