Characteristics And Component Analysis Of Microplastics Exposure In The Lower Respiratory Tract Of Smokers

Background Microplastics(MPs)was first proposed by Thompson et al in the journal Science,referring to tiny plastic fragments,fibers,particles,and other shapes with a size smaller than 5 millimeters.As a new persistent environmental pollutant,MPs have received increasing attention due to their widespread presence in various environmental media such as oceans,soils,and air.In recent years,MPs have also been found in a variety of foods,condiments,drinking water,and personal care products,which means that we inevitably ingest them through breathing,diet,and direct contact in our daily lives.Compared with external exposure to MPs,determining the internal exposure characteristics of MPs can better reflect the true absorption and accumulation dose of MPs,which can help reveal potential human health effects.However,there are few studies on the internal exposure to inhaled MPs.Experiments have shown that each cigarette releases about 100 microplastic fibers per day,and with approximately 4.5 trillion cigarette butts discarded every year,so the role of smoking as a source of MPs in human inhalation cannot be ignored.Recent studies have found more types of MPs in smokers’ sputum,and higher concentrations of fiber MPs in smokers’ BALF,suggesting that smoking may promote the inhalation of MPs.But there is a lack of direct research evidence on the characteristics of microplastic inhalation through smoking.Objective This study aims to evaluate the internal exposure levels of respiratory MPs among different populations and clarify the internal exposure characteristics of respiratory MPs in smokers.The study further explores the impact of smoking on inhalation of MPs through simulating active smoking experiments.Methods This study employed a combination of population epidemiology and in vitro experiments as research methods.We recruited subjects from The Fifth Affiliated Hospital of Sun Yat-sen University in Zhuhai,China,using a standard questionnaire to collect demographic and lifestyle information,as well as collecting bronchoalveolar lavage fluid(BALF)samples.We collected smoke by simulating active smoking and transferred MPs from the smoke to filters.All BALF and filter samples were pre-treated to remove impurities.The study used a more objective method,laser infrared spectroscopy,to detect microplastic content in BALF and filters.During sample collection and detection,we implemented a series of quality control measures to reduce plastic pollution.The study first compared the distribution differences in basic characteristics between the smoking and non-smoking groups,then evaluated the exposure levels of MPs in BALF among different populations,and further analyzed the differences in respiratory microplastic exposure between smokers and non-smokers.Next,we analyzed the characteristics of MPs in the simulated active smoking model and compared the differences in MPs between the cigarette smoke group and the control group to explore the impact of smoking on inhalation of MPs.Results A total of 31 individuals were included in the study for further analysis.Among them,16 were smokers(51.6%)and 15 were non-smokers(48.4%).The average age of all subjects was 58.5 years(ranging from 32 to 74 years),with most(77.4%)being diagnosed with lung cancer.There were differences between the smoking and nonsmoking groups in terms of gender and alcohol consumption.MPs were detected in all BALF samples in this study.Among them,the smoking group had 27 types of MPs in their BALF,with a total of 1225 particles.The most abundant type was polyurethane(PU,548 particles,44.73%),followed by polyethylene(PE,379 particles,30.94%)and silicone(SIL,52 particles,4.24%).The particle size mainly ranged between 20-100 μm(94.78%),with a median value of 32.16 μm and an interquartile rang of 23.29 μm.As the particle size increased,the number of MPs decreased.Fibrous MPs accounted for 92 particles(7.51%).The non-smoking group had 17 types of MPs in their BALF,with a total of 1821 particles.The most abundant type was PU(622 particles,34.16%),followed by PET(473 particles,25.97%)and PE(313 particles,17.19%).The particle size mainly ranged between 20-100 μm(92.26%),with a median value of 33.85 μm and an interquartile rang of 27.70 μm.Smaller-sized MPs were more abundant.Fibrous MPs accounted for 98 particles(5.38%).Compared with the non-smoking group,the smoking group had significantly higher concentrations of total MPs(median value [interquartile rang]: 12.69[36.92] particles/g),PU(4.97[11.45] particles/g),SIL(1.03[1.88] particles/g),and MPs with a size range of 20-100 μm(12.13[35.61] particles/g)(all P values < 0.05)in BALF.Furthermore,SIL concentration was moderately positively correlated with smoking index(r=0.51,P=0.01).In the simulated active smoking model,the cigarette smoke group had higher quantities of total MPs,PU,SIL,and MPs with a size range of 20-100 μm than the control group(all P values < 0.05),consistent with the results from human BALF samples.These findings suggest that smoking may promote the inhalation of total MPs,PU,SIL,and MPs with a size range of 20-100 μm,and SIL may directly come from cigarettes.Conclusion 1.MPs were found in the BALF of both smoking and non-smoking groups.The particle sizes of MPs in the respiratory tract of both groups mainly ranged from 20-100 μm,with microplastic content increasing as the particle size decreased.The main types of MPs in both groups were PU and PE,while fibrous MPs were present at a lower proportion.2.Epidemiological studies and simulated smoking experiments have consistently found that smokers have higher concentrations of total MPs,PU,SIL,and MPs with a size range of 20-100 μm than non-smokers,suggesting that smoking may promote the inhalation of total MPs,PU,SIL,and MPs with a size range of 20-100 μm.This indicates that smoking is a potential source of inhaled MPs.3.The SIL concentration in the smoking group in BALF was higher than that in the non-smoking and control groups,with no difference observed between the nonsmoking and control groups.Moreover,SIL concentration was moderately positively correlated with the smoking index,indicating that SIL may directly come from cigarettes.