Environmental Behavior Of Typical Pesticide In Soil Of Coastal Wetland Area

With the important ecological fuction and the land resources value,coastal areas now facing great challenges in regard to organic contamination by rapid reclamation and industrialization.The environmental behavior of pesticides in costal wetland area are key role of both ecological environmental protection and reasonable utilization.Mesotrione(2-[4-(methylsulfonyl)-2-nitrobenzoyl]-1,3-cyclohexanedione)is a selective herbicide,which belongs to the triketone group,was developed as a substitution of atrazine for broadleaved weed and selected annual grasses control in maize field.For it's widely use since 2012,the consumption of mesotrione was indeed increasing regularly in China.As a new herbicide,there were few reports about the environmental behaviors and dissipation of mesotrione until now.The adsorption and transportation behavior of mesotrionein silty clay soil of Yancheng coastal wetland area were investigated in this study.And the heterogeneous photodegradation on soil mineral surface and the responses of soil microbial communities and enzymes activity to application of herbicide mesotrione were also concerned.The following aspects are obtained in this dissertation:1)The adsorption behavior of mesotrione on silty clam soil form Yancheng coastal reclamation area was obtained.The results of batch experiments indicated that herbicide mesotrione was difficult to adsorbed by soil with the corresponding adsorption coefficient K_d was in range of 3.110 ~ 3.854 L/kg.The variations of Gibbs free energy?G of mesotrione on Yancheng silty clay soil were calculated in range of-18.23 ~-19.97 kJ/mol,indicating that the adsorption was endothermic,spontaneous and physical process.A new unify kinetic adsorption model was proposed and analyzed for experimental data,which was suitable applied the adsorption process.Compared to Yixin paddy soil,the effect of pH,organic matter content,which were account for the variance in adsorption were also discussed.2)The mobility of mesotrione on slity clay loam under the dynamic conditions were obtained.The results form column experiments and CXTFIT model indicated that mesotrione was easily reaches the lower surface soil forits lower adsorption capacity by Yancheng slity clay soilwith the retardation factor Rd of 12.48~14.23.The nonequilibrium convection-dispersion model were well fitted the asymmetrical BTCs of mesotrione,which indicating rate-limited desorption,were dominated by both physical and chemical non-equilibrium adsorption.Msotrione was easy to be leached into the bottom of the columns under artificial rainfall were applied,After 300 mm continuous rain leaching,more than 86 % mesotrione retented in under 15 cm layersindicating higher risk to grounderwater.3)The responses of microorganisms and enzymes activity of Yancheng coastal silty clay soil to mesotrione were obtained using a laboratory microcosm approach.The results indicated that mesotrione would not affected microbial communities and enzymes activities only at doses under the recommended field rates.The rate of microbial population was affected by the doses of mesotrione.At the dose of 100-400 ?g/kg,the population of bacterial and actinomycetes were increased during first 3 days and then recovered smoothly,while the population of fungi first decreased during first 3 days and then increased when compared with control.The activities of catalase,alkaline phosphatase and polyphenol oxidase were enhanced while the activities first decreased and then enhanced influenced by mesotrione when compared with control.Maximum dissimilarity of enzyme activities of catalase,alkaline phosphatase and polyphenol oxidase between control and 400 ?g/kg trated soils did not exceed 96.0 %,142.3 % and 235.6 %,respectively.Inhibitory rate on activity of urease did not exceed 28.15 % during first 3 days,and then recovered smoothly.4)The heterogeneous photodegradation behavior of mesotrione under UV light irradiation on the surface of soil minieral were obtained,and reaction mechanism of?-Fe2O3-oxalic acid photochemical system were also investigated.The rate of direct photodegradation of mesotrione was only 6.8 % under 60 min irradiation.The addition of iron oxide and oxalic would markedly accelerated the degradation of mesotrione with 85.9 % under 60 min irradiation.However,excessive oxalic acid and iron oxide inhanced the photodegradation.The photodegradation were varied with the formation of mesotrione,there was nearly no degradation with its iron form.The variations of TOC and pH,the concentration of ·OH were also investigated to demonstrated the existence of Fenton-like system.The mechanism of heterogeneous photodegradation on surface of soil mineral was also proposed.