Study On The Pollution Characteristics,formation Mechanism And Biotoxicity Of Environmental Persistent Free Radicals In PM_2.5of Zhengzhou City

Environmental persistent free radicals are a new class of environmental risk substances,which can stably exist in atmospheric particles,and are considered to be the key factor leading to human pneumonia and lung cancer.Toxic elements and organic pollutants contained in PM2.5 have been extensively studied,but there is very limited information on environmental persistent free radicals(EPFRs)associated with PM2.5.Therefore,this paper takes Zhengzhou City,Henan Province as the research object,analyzed the concentration level,type,decay life and biotoxicity of environmental persistent free radicals in PM2.5 in Zhengzhou City,and systematically discusses the influence of transition metal oxides and their ions,precursor concentrations and pyrolysis temperature on the formation of EPFRs by simulating the generation of EPFRs.The main conclusions are as follows:(1)During the study period,the concentration of environmental persistent free radicals in spring in Zhengzhou ranged from 1.73×1012 spins/m3 to 6.48×1013 spins/m3,and the g factor ranged from 2.0032 to 2.0041.Carbon-centered free radicals with a nearby heteroatom(semiquinone free radicals)and oxygen center free radicals were the main types.In summer,the concentration of EPFRs ranged from 1.76×1012 spins/m3 to 5.25×1013 spins/m3,and the g-factor ranged from 2.0030 to 2.0035,all of which were semiquinone free radicals.In autumn,the concentration of EPFRs ranged from 9.23×1014 spins/m3 to 1.32×1016 spins/m3,and the g-factor ranged from 2.0031 to 2.0036,all of which were semiquinone free radicals.In winter,the concentration of EPFRs were between 9.98×1015 spins/m3 and 2.22×1017 spins/m3,and the g-factor were between 2.0029 and 2.0035,which were mainly the free radical of semiquinone and carbon center.At different seasons,the EPFRs shows the distribution characteristics of high concentration in autumn and winter and low concentration in spring and summer.(2)In order to explore the formation mechanism of EPFRs,this paper prepared EPFRs with catechol and silica as simulation system under the condition of isolated oxygen,and discussed the influence of precursor catechol content,transition metal ions and their oxides and pyrolysis temperature on the formation of EPFRs.The results showed that both transition metal oxides and metal ions can promote the formation of EPFRs,but the former is more effective.The concentration of the precursor catechol and the pyrolysis temperature were also important factors promoting the formation of EPFRs.With the increase of the concentration of catechol and the pyrolysis temperature,the signal intensity of EPFRs both increased at first and then decreased.When the pyrolysis temperature was 400℃ and the mass ratio of catechol to carrier silica was 0.016,the EPFRs signal intensity reached the maximum,which was 1.903 × 1014 spin/m3.(3)In aqueous solutions,EPFRs can directly produce reactive oxidizing species(ROS),such as hydrogen peroxide,hydroxyl radicals,and peroxides,which can cause DNA damage.Therefore,this paper explored the effects of EPFRs in PM2.5 on human lung cancer cells and chinese little greens.Through analysis of cell activity,intracellular ROS concentration levels and cell apoptosis datas,the results showed that EPFRs can promote the rise of intracellular ROS,thereby promoting oxidative stress response of cells,leading to cell apoptosis.When the concentration of EPFRs reached 80 μg/mL,the survival rate of cells decreased to 10%.Finally,the effects of simulated EPFRs on the germination rate of plant chinese little greens were investigated.The results showed that when the content of EPFRs reached 80 mg,the germination rate of chinese little greens decreased to 35%,and the roots of germinated chinese little greens were shorter and thinner than the blank control,indicating that a higher concentration of EPFRs would also affect the growth of plants.In conclusion,by studying the pollution characteristics,formation mechanism and biological toxicity of EPFRs in PM2.5 in Zhengzhou,basic data can be provided for potential environmental risks,so as to reduce potential risks to human health caused by exposure to EPFRs.