Degradation Mechanism And Eco-toxicity Assessment Of Pyrrole Fungicides And Pharmaceuticals In The Aquatic Environment

In recent years,many trace organic pollutants have been detected in wastewater,seawater,surface water and drinking water all over the world,including drugs.hormones,pesticides and industrial pollutants.Regardless of their relatively low occurrence(few ng L-1 to several ug L-1),trace organic pollutants in aquatic resources have been a growing concern due to their potential adverse effects on human health and ecosystem,such as endocrine disruption,spread of antibiotic resistance,and bioaccumulation.Fungicides commonly used in agriculture and pharmaceutical and personal care products(PPCPs)commonly used in human and animal husbandry are among these pollutants.Fungicides and PPCPs are widely distributed in the environment.Both of them have favorable effects on specific target organisms,but their ecological toxicity to non-target organisms after being discharged into water bodies is not clear.Fungicides are commonly used to avoid fungal damage to plants and are widely used in the treatment of seed plant leaves in agriculture.Indirect photodegradation is the main pathway for the degradation and transformation of fungicides in natural water bodies,which can be absorbed into soil particles or dissolved in water and enter larger water systems with surface runoff.And a lot of PPCPs ends up in wastewater and ends up in sewage treatment plants.Conventional biological and chemical treatment processes have a very low degradation efficiency of PPCPs,and advanced oxidation process(AOPs)plays an important role in the removal of refractory or non-biodegradable pollutants in water.In the process of AOPs,strong oxidants can be generated,such as hydroxyethyl ·OH,SO4·-,·Cl,·ClO and other derived radicals.These highly active radicals convert refractory organic pollutants such as PPCPs into various byproducts through complex reactions.During the degradation of fungicides and PPCPs,the transformed products may retain the toxic properties of the parent compounds or become more biologically active.Therefore,the prediction of the toxicological effects of trace organic pollutants in various environmental substrates is increasingly applied to their biological impact assessment.This paper used the quantum chemistry calculation method to study the degradation mechanisms triggered by different oxidant of the typical pyrrole fungicides(fludioxinil and fenpiclonil)and common drugs(SMX,IMP and DCF).And the transition state theory(TST)is used to calculate the dynamic data to get the reaction rate constant.The long-term stability of organic pollutants in the environment may cause potential harm to the ecosystem and human health.Thus,the computational toxicology method was used to predict and evaluate the ecological toxicity of various original pollutants and their transformed products.The main content and conclusion of the study include the following four aspects.1.Indirect photodegradation mechanisms of fludioxonil by ·OH and 1O2Fludioxonil is a broad-spectrum fungicide commonly used in agriculture to protect fruit and vegetable crops.It can be transported to large water environments by surface runoff,raising concerns about the potential environmental toxicity of roccitrile to non-target organisms in aquatic environments.In this study,quantum chemistry and computational toxicology methods were used to systematically study the initiation mechanism of ·OH and 1O2.The results showed that the most favorable initiatory reaction paths of ·OH and 1O2 occurred at the sites on the pyrrole ring.According to the kinetic calculation results,the degradation rate constants of ·OH and 1O2 at 1 atm and 298 K were 1.23×1010 and 3.69×107 M-1 s-1,respectively,which were on the same order of magnitude as the experimental data.According to the toxicity assessment of ECOSAR,acute and chronic toxicity levels of the degradation products of fludioxonil were decreased,but most of the products were not completely harmless.This study further revealed the indirect photochemical transformation mechanism of fludioxonil in the aquatic environment at the microscopic level.2.1O2,·OH and SO4·--initiated degradation mechanisms of fenpiclonilFenpiclonil is an agricultural phenylpyrrole fungicide,and its ecological toxicological effects have drawn increasing attention.This chapter studies the indirect photochemical transformation mechanism of fenpiclonil in aquatic environments caused by different active oxidants(1O2,·OH and SO4·-)and ecological toxicity Quantum chemical calculation results show that 1O2 can form internal peroxides by cycloaddition reaction with pyrrole ring.The results show that ·OH initiation reaction rate constant(2.26×109 M-1 s-1,298 K)is higher and plays a leading role in the indirect photodegradation process of fenpiclonil.The kinetic calculation results showed that high temperature was more conducive to the degradation of fenpiclonil.In order to better understand the environmental impact of fenpiclonil,we calculated the subsequent degradation transformation by IM10,which was formed at the fastest reaction rate,and predicted its ecological toxicity with computational toxicological ECOSAR and TEST software.The results showed that the aquatic toxicity of the degradation products decreased with the degradation process,especially the pyrolysis products(TP3 and TP4)This study provides guidance for further experimental study of fungicides degradation from the perspective of theoretical calculation3.·OH-initiated degradation mechanisms of SMX and TMPBacteriostatic antibiotics such as sulfamethoxazole(SMX)and trimethoprim(TMP)are often present in wastewater and surface water,which has aroused people's concern about their ecotoxicological effects.The results showed that the most favorable conversion pathways for SMX and TMP were-OH addition reactions at the benzene ring with the lowest Gibbs free energy barrier(6.86 kcal mol-1 and 6.21 kcal mol-1).It was found that at 298 K,the total reaction rate constants of SMX and TMP in the initial reaction with-OH were 1.28×108 M-1 s-1 and 6.21×108 M-1 s-1,respectively.By comparing the ecotoxicity of the transformed products with SMX and TMP,it was found that the acute and chronic toxicity of the degraded products were reduced.However,some products are still at toxic levels to target organisms,especially daphnia.This study provides a deeper understanding of the degradation mechanism of SMX and TMP in aquatic environments through theoretical calculation4.·OH,·ClO and SO4·--initiated degradation mechanisms of DCFDiclofenac(DCF)is an anti-inflammatory drug that is popular around the world.In this study,the reaction mechanisms of DCF by ·OH,·ClO and SO4·-were investigated by quantum chemistry.And the eco-toxicity of DCF and its degradations products were predicted using QSAR models.The quantum chemical mechanism shown that the addition reaction of ·OH and the single electron transfer reaction of SO4·-play an important role in the indirect photodegradation of DCF.The overall reaction rate constants of ·OH/·ClO/SO4·--initial reaction of DCF are 1.12×109?2.30×106?1.30×108 M-1 s-1,respectively.The reaction of DCF with ·OH is 1-3 orders of magnitude faster than the reaction of ·ClO and SO4·-,which also proves that ·OH-initiated reaction play a dominant role in the degradation process of DCF.Studies on subsequent transformation of DCF revealed that hydroxylation products(P1,P2,P5),·ClO addition products(P3,P4)and cleavage benzene ring products(P6,P7)could be formed.In terms of acute and chronic toxicity,DCF is classified as a harmful compound.The toxicity of hydroxylation and 'ClO addition products decreased with the degradation process,but the toxicity of benzene ring products was higher than that of DCF.DCF and their transformed products still have developmental toxicity.Therefore,more attention should be paid to the environmental chemical behavior and degradation pathways of DCF in aquatic environments.