Studies On The Degradation Of Endosulfan And Chlorfenapyr By Zero-Valent Zinc In Water And Soil

Chemical pesticides regarded as the guarantee of a good harvest are widely used all over the world.It has brought great benefits to humans,but also some negative effects.Excessive and unreasonable use of pesticide has caused many serious consequences to our human and ecological environment,and the problem of pesticide pollution has become a focus in the world.Endosulfan was an efficient broad-spectrum organochlorine pesticide.But endosulfan has been included in the list of persistent organic pollutants(POPs)in 2011,because it possessed the character of persistence in the environment,bio-accumulation,high biological toxicity,carcinogenicity and endocrine interferon.Chlorfenapyr was a novel broad-spectrum aryl pyrrole insecticide-acaricide.Due to its widespread use,the problems about environmental pollution and the residue in agricultural products become more prominent.It is with high toxicity to hydrobiology,bees and quail.However,the study about the degradation of chlorfenapyr in the environment has been reported less until now.The technology about using zero-valent metals removal the pollutants was developed in recent years.It is believed that zero-valent metal has wide application prospect due to its efficiency in reductive degradation on many organic products and in situ remediation of groundwater,along with low cost and simple processes.Zero-valent zinc was an effective reducing agent for endosulfan and chlorfenapyr in water and soil.This paper mainly studied the factors and reaction mechanisms of the degradation of endosulfan and chlorfenapyr by zero valent zinc in water and soil.The thesis includes two parts.1.The degradation of endosulfan by zreo-valent zinc in water and soil Zreo-valent zinc was used to degrade endosulfan in water and soil,and the effectfactors and reaction mechanism were studied.(1)More than 90%endosulfan could be degraded in 180 min.(2)The lower pH,the more efficient endosulfan degradation in water and soil.The pH of the system was gradually increased,closely related to the trend of endosulfan degradation.At the beginning of the reaction,the pH rose rapidly and a large number of hydrogen ion was consumed in the process of the conversion of zinc into zinc ion.Then the degradation rate decreased and the change of the pH value also became steady.(3)The existence of dissolved oxygen would inhabit the degradation of endosulfan in water,especially for β-endosulfan.(4)The use of Zn(0)was more effective than Fe(0)for the degradation of endosulfan.(5)In soil,the cationic surfactant and the nonionic surfactant accelerated the degradation reaction,while the anionic surfactant inhibited the degradation reaction.The reason for the acceleration of CPC and TW-20 was speculated to the electrostatic interaction between its positive head group and the chloride group of endosulfan.(6)The half-life was decreased with the increment of Zn(0)at the dose of 0.1 g to 1 g in soil.With the increment of Zn(0),more active sites were provided to endosulfan.(7)There was no significant effect from the nature of the soil in the endosulfan degradation.(8)The degradation pathway of endosulfan was speculated.Four chlorine of endosulfan were proposed to be reduced and 5,6-hexachloro-8,9,10-trinorbom-5-en-2,3-ylenebismethylenes sulfite was generated.2.The degradation of chlorfenapyr by zreo-valent zinc in water and soilZreo-valent zinc was used to degrade chlorfenapyr in water and soil,and the effect factors and reaction mechanism were studied.(1)The lower pH,the more efficient chlorfenapyr degradation in water and soil.(2)The existence of dissolved oxygen would inhabit the degradation of chlorfenapyr:the degradation rate can reach 95.91%without dissolved oxygen,but just 89.83%with the existence of dissolved oxygen.(3)The use of Zn(0)with a half-life of 51.70 min for chlorfenapyr degradation was more effective than Fe(0)with a half-life of 173.30 min.Under the same conditions,the degradation of Zn(0)was significantly stronger than Fe(0).(4)The half-life was decreased with the increasing the dose of Zn(0)at the range from 0.1 g to 1 g.Appropriate dose of zinc powder was an important factor to ensure the efficient degradation.(5)There was no significant effect from the nature of the soil in the chlorfenapyr degradation.(6)Bromine atom of chlorfenapyr was proposed to be reduced and 2-(4-chlorophenyl)-1-ethoxymethyl-5-trifluoromethylpyrrole-3-carbonitrile was generated.