Exposure Of Lead And Cadmium In Atmospheric Particulate Matter PM_2.5 In Human Respiratory Tract And Health Risk In Metallurgical Area

PM_2.5,as an inhalable particle could enter and deposit in the lungs with respiration,and has attracted wide attention due to its large specific surface area,which can carry more harmful substances.As one of the important components of PM_2.5,heavy metals have many sources,strong bioaccumulation,and are not easy to discharge from the body,and can promote the inflammatory response of cells and the overexpression of some proteins,couse human diseases.Pb is an important pollutant in atmospheric environment and one of the toxins that can cause developmental neurotoxicity,long-term exposure to Pb will cause damage to human nervous system and vascular system.As a carcinogen,Cd is also one of the by-products of zinc smelting,which can bind metallothionein more effectively than zinc,so that it accumulates in the human body and causes tissue damage,which has caused extensive research by scholars.The respiratory system is the most direct and important exposure site of PM_2.5,and the prevalence rate of respiratory is also related to PM_2.5.Currently,the existing human health risk assessment on the inhalation route of heavy metals in PM_2.5 mostly uses the total concentration of heavy metals as the exposure dose.However,only part of the particles can be deposited in the respiratory tract,and the heavy metal components are not all dissolved in the respiratory tract,and participate in systemic circulation due to the influence of the deposition environment and the properties of heavy metal components.This also makes it possible that previous studies may have overestimated the health risk assessment of inhalation routes,and thus may have overset the requirements and limits of air pollution control programs.Therefore,the study on the exposure characteristics of heavy metals in PM_2.5 in the respiratory tract and the modification of the exposure dose in human health risk assessment of inhalation routes can determine the harm of heavy metals to the human respiratory tract and reduce the impact of excessive risk assessment results on the formulation of atmospheric environmental control requirements.In China,metal smelting and coal combustion are the main sources of heavy metals in the atmosphere.Therefore,Huludao Metallurgical region is selected as the research area,the spatio-temporal variation rule is analyzed,and the main pollution sources of heavy metals are discussed.The deposition fraction of different respiratory rate,respiratory cycle and incident particle number in human respiratory tract model was discussed by using computational fluid model.At the same time,the in vitro bioaccessibility simulation process of respiratory system was supplemented and improved,and the bioaccessibility of Pb and Cd in PM2.5 was analysed and determined.Finally,based on Pb and Cd bioaccessibility and particulate deposition fraction,the exposure dose of inhalation pathway was modified,and the human health risk model of inhalation pathway in the study area was established to evaluate the health hazards of heavy metals to human inhalation pathway.The average annual concentration of PM_2.5 in the study area was 47.71μg/m³,which was higher in autumn and winter than in spring and summer,and showed a steep increase after the heating period began.In the non-heating period,the concentration of PM_2.5 in the Huagong Hospital was higher than that in the Xinqu Park;In the heating period,the difference of average PM_2.5 concentration between sampling points was small.There were differences among the concentrations of heavy metals（p<0.05）.In the non-heating period,heavy metals in PM_2.5 in the study area were mainly from traffic emission,during the heating period,heavy metals in PM_2.5 in the study area were mainly from coal combustion.The respiratory system is the most direct exposure site of PM_2.5,and particulate matter is successively deposited in the nasopharynx,tracheobronchus and lung gland regions along with respiration.The results of this study show that the respiratory rate has the most significant effect on the pressure and flow velocity of the respiratory system,and the increase of the respiratory cycle can prolong the particle movement time,and promote the increase of the deposition fraction and deposition fraction of particles.The decrease of incident particle number enhanced the disorder of particle deposition,which significantly affected the particle deposition fraction in the upper respiratory tract,while the particle deposition fraction in the lower respiratory tract remained basically unchanged,and only affected the contribution distribution of sediment fraction in each region.When the respiratory cycle was 4 s and the respiratory rate was 15 L/min,the deposition fraction of upper respiratory tract and tracheobronchus were 5.26%and 3.89%.When the respiration rate was 30 L/min,the deposition fraction was 6.44%and 6.42%.Light exercise may cause more particulate matter to be deposited in the respiratory system than rest,resulting in more serious harm to the human respiratory system.In this paper,ANF,ALF and GS were selected to form the respiratory system simulation solution in vitro.Affected by pollutant composition,solution component,p H and simulation duration,Pb and Cd deposited in respiratory tract particles have different solubility in human body.The bioaccessibility of Pb was higher than that of Cd in both the upper and lower respiratory tracts,and higher in the non-heating period than in the heating period.The bioaccessibility of heavy metals in particulate matter in artificial lysozyme fluids was higher than that in Gamble solution.Cd is the most harmful to human pulmonary acid deposition environment.Pb is more likely to harm human trachea and bronchus,and the harm to human pulmonary deposition environment is higher than that of neutral deposition environment.The daily exposure concentration and dose of inhalation pathway were modified by particulate matter deposition fraction and bioaccessible concentration of heavy metals to explore the health risks of inhalation pathway in the study area.The results based on the exposure concentration parameters of the two heavy metals show that heavy metals may produce non-carcinogenic risk and potential carcinogenic risk for children and adults in the study area,and the non-carcinogenic risk index in the heating period is higher than that in the heating period,and the non-carcinogenic risk index in the light exercise state is higher than that in the rest state.Comparing the health risk assessment results of inhalation routes with different exposure concentrations,the health risk uncertainty of exposure concentrations based on total concentration and particulate deposition fraction is higher for the same respiratory rate.