Distribution Characteristics And Toxicity Of Persistent Organic Pollutants In The Northern Edge Of Sichuan Basin

To explore the vertical distribution characteristics of atmospheric persistent organic matter in the northern edge of the Sichuan Basin and the toxic effects of typical polycyclic aromatic hydrocarbons（PAHs）in the atmosphere of this region on human bronchial epithelial cells（16HBE）,this study conducted persistent organic matter sample collection using atmospheric passive samplers at 6 altitudes in Guanwu Mountain（mountainous area）,5altitudes in Douchui Mountain（scenic area）,and 6 different altitudes in Mianyang TV Tower（city）from September 16,2021 to December 31,2021,determination and analysis of the content and composition of PAHs,Polychlorinated Biphenyls（PCBs）,and Organochlorine pesticides（OCPs）by gas chromatography-mass spectrometry（GC-MS/MS）,using phenanthrene and fluoranthene,which account for the top two concentrations of PAHs in the atmosphere of the region,to conduct exposure experiments on 16HBE cells at different times and concentrations alone or in combination,the toxic effects of phenanthrene and fluoranthene on 16HBE cells were judged by cell survival rate,reactive oxygen species（ROS）,superoxide dismutase（SOD）,lactate dehydrogenase（LDH）,mitochondrial membrane potential and other indicators,and the adverse effects of air pollution on human respiratory tract were analyzed in combination with the survey of the number of admissions of typical respiratory diseases in this area in 2021,The main conclusions were as follows:（1）During the study period,the average mass concentrations of 16 PAHs in the atmosphere of the northern edge of the Sichuan Basin were 3.38～26.59 ng/m³,the average mass concentration of Ba P was 0.003～0.019 ng/m³,lower than the secondary standard specified in the ambient air quality standard（GB3095-2012）1 ng/m³.The average mass concentration of 18 atmospheric PCBs were 19.52～58.15 pg/m³,the average mass concentrations of 13 OCPs were 43.95～128.39 pg/m³.Basically,the atmospheric persistent organic matter concentration in mountainous areas decreased with altitude,while the persistent organic matter concentration in scenic areas increased with altitude.The persistent organic matter concentration in cities first decreased,then increased,and then decreased with altitude.According to the source analysis,the main sources of atmospheric PAHs in the northern edge of the Sichuan Basin in autumn and winter were coal combustion and traffic emissions.The main sources of atmospheric PCBs were transformer oil sources,organic pigment sources,paint sources,and waste combustion sources.The main sources of atmospheric OCPs were mixtures of dicofol and industrial DDTs,as well as historical residues of agricultural and industrial HCHs.The health risk assessment showed that the total toxic equivalent of atmospheric PAHs in the northern edge of the Sichuan Basin did not exceed the concentration limit（1 ng/m³）specified by the World Health Organization（WHO）,and the carcinogenic and non carcinogenic risks of atmospheric PCBs and OCPs did not exceed the reference values.(The reference value for carcinogenic risk was 1×10^-6,non carcinogenic risk reference value was 1).（2）Experiments on cell survival and lactate dehydrogenase activity had shown that both phenanthrene and fluoranthene alone or in combination could have toxic effects on 16HBE cells,for example,the cell survival rate decreases,the cell membrane was damaged,and the mitochondrial membrane potential decreases.As the concentrations of Phe and Fla increase,the survival rate of 16HBE cells continuously decreases,showed a certain dose-effect relationship The combination of phenanthrene and fluoranthene could enhance the toxicity to16HBE cells.In terms of reducing the survival rate of 16HBE cells,phenanthrene and fluoranthene exhibited a synergistic effect,while in terms of damage to cell membranes,the two exhibit independent or additive effects.Through oxidative stress experiments,it had been shown that both phenanthrene and fluoranthene alone or in combination could cause certain oxidative damage to 16HBE cells,manifested by an increase in ROS content and an acute increase in SOD activity.The combination of phenanthrene and fluoranthene had a synergistic effect in causing oxidative damage to 16HBE cells.（3）Through the collection and investigation of typical respiratory disease patient information from two large general hospitals in the northern edge of Sichuan Basin in 2021,daily mean statistics of atmospheric particulate matter concentration and meteorological factors,it was found that atmospheric particulate matter(PM_2.5,PM₁₀)and humidity were positively correlated with the number of hospitalized patients with typical respiratory diseases,while temperature was negatively correlated with the number of hospitalized patients;Autumn and winter were the high incidence periods of respiratory diseases,and the number of hospitalized patients with some respiratory diseases significantly increases in autumn and winter;The relatively high proportion of hospitalized patients with chronic obstructive pulmonary disease（COPD）and lung cancer were retirees from steel mills and farmers（23.21%to 35.71%）.