Study On The Toxicities To Daphnia Magna,L.hoffmeisteri And Carassius Auratus And Degradation Mechanism Of Typical Organic Phosphorus Pesticides

Organic phosphorus pesticides(OPPs)possess high efficiency,rapidity,broad spectrum,the short half-life(days to tens of days),easy degradation.OPPs as an alternative to organic chlorine pesticides,are widely applied as weeding,insecticide and sterilization in China,accounting for more than 50%of the total amount of pesticides.However,with the continuous use of OPPs,many environmental problems have been exposed,such as high residues,strong toxicity and so on.Residual pesticides in farmland soil are easy to be washed away by rainwater and surface runoff,which cause serious pollution to groundwater,surface water,rivers,lakes and coastal waters,and have toxic effects on aquatic organisms,thereby threatening the ecological environment and human health.Therefore,this thesis is about the research work of the biological toxicity and oxidative removal for agricultural common pesticides,hoping to provide the useful information for the mechanism and risk evaluation of OPPs.Concrete from the following aspects:(1)The acute toxicity of OPPs(dimethoate,acephate,trichlorphon,dichlorvos,phoxim,glyphosate,chlorpyrifos,profenofos and methidathion)to Daphnia magna and L.hoffmeisteri were determined.Then,density functional theory(DFT)and comparative molecular field analysis(CoMFA)were used to investigate relationship of the structure and toxicity for the compounds.The results showed that the toxicity of OPPs to Daphnia magna and L.hoffmeisteri were mainly related to the electronic properties of the compounds(especially the electropositivity of P atom).In addition,the biosensitivity and their interspecific relationships of these two aquatic organisms to OPPs were studied.Finally,the toxicity of different aquatic organisms is integrated,and the toxicity of OPPs is evaluated.Daphnia magna was more sensitive than L.hoffmeisteri for most OPPs,but there was a good correlation between the acute toxicity.Compared with the single biological toxicity,the result of IBS is different.Furthermore,it is necessary to take into account the differences of different organisms to evaluate the toxicity of a pollutant.(2)Study on the potential ecological risk of OPPs to aquatic organisms.Freshwater fish Carassius auratus were exposed to 0.1 and 1 mg/L(dimethoate,acephate,trichlorphon,dichlorvos,phoxim),0.1 and 0.01 mg/L(glyphosate,chlorpyrifos,profenofos and methidathion)for 15 d.The oxidative stress induced in livers of Carassius auratus was assessed using three biomarkers,including superoxide dismutase(SOD),reduced glutathione(GSH)and malondialdehyde(MDA).The integrated biomarker response(IBR)was applied to assess the overall antioxidant status in fish.The results showed that the response of antioxidant enzymes exposed different compounds are diversity.Glyphosate,chlorpyrifos and methidathion significantly induced the activity of SOD after 4-day exposure.And prolonged exposure(15d),the enzyme form the group treated with this compounds were inhibited.MDA(after 4-day exposure)of almost exposed groups were significantly induced,but were inhibited after 15 day.Prolonged exposure can produce an excess of ROS,which ultimately leads to oxidative damage to the liver of C.auratus.According to their IBR values calculated,the hepatic oxidative toxicity followed the order:profenofos>chlorpyrifos ? glyphosate>phoxim>dichlorvos>thichlorphn.In short,the production of free radicals may be one of the mechanisms which OPs affect C.auratus.(3)In order to study the effect and mechanism of OPPs on acetylcholine enzyme(AChE),the activity of AChE were determined after exposure to different concentrations.The activity of AChE was closely related to the species,concentration and time.At the same time,9 OPPs pesticides were docked into the acetylcholine enzyme with Surflex-Dock.The results showed that the hydrogen bond was formed between the receptors and the pesticides with highest score except of profenofos,and the number without hydrogen bonds in the 20 conformations was below 10.In this study,the amino acids residuals forming hydrogen bonds were found in catalytic triad,choline binding site,oxyanion hole and peripheral anionic site of the active pocket.Thus,we speculate that there may be a different effect of pesticides and receptors.(4)Study on the mechanism of oxidative degradation of parathion(PTH)by potassium ferrate.The removal of PTH at an initial concentration of 5 mg/L could reach 99%in 300 s under the conditions of[Fe(VI)]:[PTH]15:1;T = 25 ? and pH = 7.0.The presence of HCO3-,Ca2+,Cu2+,Fe3+ and HA decreased the removal efficiency of PTH.Six oxidation products were identified by liquid chromatography-time-of-flight-mass spectrometry(LC-TOF-MS),and cleavage of ester bond and sulfur-oxygen substitution reaction were mainly involved in the reaction process.Toxicity evolution by luminescence test showed that the oxidation of PTH by Fe(?)can decrease potential aquatic ecological risk.(5)The kinetics,mechanism and degradation products of chlorpyrifos were systematically investigated using ferrate(VI).A series of kinetic experiments were conducted to evaluate the influence of various environmental factors,such as pH,oxidant dosages,as well as the presence of anions,cations,humic acid(HA),and different water matrices.The degradation efficiency of chlorpyrifos was not affected by the addition of Cl-,SO42-,NO3-,HCO3-,Fe3+,Cu2+,or NH4+,but it was inhibited by the presence of Ca2+,Mg2+,and HA.Ten oxidation products of chlorpyrifos were identified using liquid chromatography-quadrupole-time-of-flight-mass spectrometry(LC-Q-TOF-MS),and their structures were further elucidated using MS/MS spectra.Then,two degradation pathways were preliminarily proposed including the oxidation of the P=S bond,cleavage of C-O bond,and hydroxyl substitution reaction,and were further confirmed based on frontier electron density calculations and point charges.Furthermore,experiments on removing chlorpyrifos(1 uM)from tap water,river water,and synthetic wastewater were performed to demonstrate the practical applications of Fe(VI).(6)Persulfate(PS)activation by zero-valent iron powder was used to to degrade Fenitrothion(FNT),a common organophosphorus pesticide.The addition of FeO significantly enhanced the oxidation efficiency of PS towards FNT.And SO4-played a leading role in decomposing FNT.The degradation efficiency of FNT was inhibited by the presence of HCO3-and FA.Twelve transformation products of FNT were identified,and most of them are hydroxylated derivatives.Particularly,several newly proposed products were determined in this work.The calculated 2?(CriHOMO)2 values successfully predicted the most reactive sites of FNT where reaction products generated.Toxicity predictions by the ECOSAR program indicated that the ecotoxicity of FNT could be decreased by the Fe0/PS treatment.In summary,the first three parts of this study were aimed at the toxicity of organophosphorus pesticides to aquatic organisms.IBS and IBR of several organophosphorus pesticides were established,which can effectively solve the problem that it is difficult to evaluate the toxicity of a single organism because of the difference of toxicity among species.The last three parts are about the degradation of three kinds of highly toxic organophosphorus pesticides.The degradation process of organophosphorus pesticides in water environment was systematically studied.It is found that free radicals play an important role in the degradation of organophosphorus pesticides,and the coexisting components in real water will affect the degradation process,which can provide reference information for the study of the transformation behavior of organophosphorus pesticides in real environment.