Removal Of Chlorpyrifos Via Thermo Activated Persulfate Oxidation Processes In Water And Soil

Organophosphorus insecticide,due to high efficacy,widespread application and easy decomposition,is widely used in prevention and control of plant diseases and insect pests.Low-dose residual has significant biological toxicity,causing the adverse effects on human health via the food chain or direct contact such as immunity decline,developmental malformation and depression.China with hundreds of production factoriesis the largest country in the production of the chlorpyrifos in the world,accounting for more than one-third of the global total.In recent years,due to various reasons,which led to an increase in the number of cut-off and the relocation of the company,the legacy site where the contamination of soil and groundwater have a serious threat to the ecological environment and biological health.Currently,the methods of removal of chlorpyrifos are mainly biodegradation and chemical oxidation degradation,chlorpyifos of contaminated sites can be decomposed into CO2 and H2O via bioremediation,but its operation must comply with the special conditions of the pollution,and the need for high technical content.Chemical oxidation,remediation time is short,high efficiency,and persulfate as the latest research in situ chemical oxidant,SO4-· is more stable and suitable for a wider range of pH.In this paper,degradation efficiency and possible degradation pathway of chlorpyrifos via thermo activated persulfate oxidation processes in water and soil were investigated.We attempt to provide important reference for development of remediation technology of chlorpyrifos and other organophosphorus pesticides in soil and groundwater.The main results were as follows:（1）The influences of temperature,concentrations of potassium persulfate,pH values,and common anions(i.e.CO₃^2-,HCO₃^-,Cl-and SO42-)on the degradation of chlorpyrifos were investigated in water.The results indicated that the degradation of chlorpyrifos followed pseudo-first-order kinetics.The reaction rates increased with increasing concentrations of persulfate.Temperature versus chlorpyrifos degradation rates was fitted well with the Arrhenius model.The change of pH values has no significant effect on the degradation of chlorpyrifos.As to four kinds of common ions in natural water,apart from SO42-having no effect on the degradation,Cl-can promote the degradation of chlorpyrifos,while CO₃^2-and HCO₃^-inhibited the degradation and the degree of inhibition was CO₃^2->HCO₃^-.Quenching experiment was employed to verify the presence of free radicals in the systems,and confirmed that SO4-· was the main active substance.（2）Five kinds of degradation products of chlorpyrifos were detected by LC-MS.Peaks of other products were clearly separation except for the peak of the two products in TIC.Molecular structure of these products was identified according to the molecular weight,and possible degradation pathways were proposed.Five kinds of products were:Cl O,O-diethyl-O-2-pyridyl thiophosphate,C2 O,O-diethyl-O-2-pyridyl phosphate,C3 OI,O-diethyl-O-5,6-dichlone-2-pyridyl phosphate,C4 O-ethyl-O-3,5,6-trichloro-2-pyridyl phosphate,C5 0,0-diethyl-0-3,5,6-trichloro-2-pyridyl phosphate.Method and route of degradation:Chlorpyrifos formed two products C5 and C1 through oxidation and dechlorination,C5 again formed three other products C2,C3 and C4 after dechlorination and hydrolysis,C2 can also be transformed by C1 and C3.According to the structure of intermediate product,we can conclude that the toxicity for:The toxicity of the products C2,C3,C5 and C4 may be more severe than chlorpyrifos and C1.Three chlorine atoms on the benzene ring are disappeared on the product C1,compared with chlorpyrifos,its toxicity can be considered to be similar or slightly weakened because P=S key is not damaged.P=O key is existed in the products C2,C3,C4,C5,but other groups structure is similar,so the toxicity of the four kinds of products are identical.With the continued progress of the reaction,retention time of toxic products in the environment become short,and toxic product can be broken down into non-toxic small molecules by hydrolysis,oxidation and dechlorination.（3）The influences of temperature,concentrations of potassium persulfate,soil organic matter,iron content on the degradation of chlorpyrifos were investigated in the simulated contaminated soil.The results indicated that persulfate and the degradation rates of chlorpyrifos was a linear relationship in a certain concentration range when the temperature and the concentration of the substrate were constant,and the concentrations were higher,the rates became faster.There was a great influence of temperature on the degradation of chlorpyrifos,with the increase of temperature,degradation rates of chlorpyrifos accelerating significantly.Soil organic matter can be oxidized by persulfate,resulting in the decrease of persulfate concentrations,that is,degradation rate and half-life of chlorpyrifos became slower and longer,respectively.Degradation of chlorpyrifos can be also inhibited in the presence of iron content.