| Objective:In 2021,the plastic production in the world reached 391 million tons,while only 10.2 million tons of plastic products were recycled.High production and low recovery lead to a large amount of plastic waste into the environment,which produces microplastics with particle size less than 5 mm under the action of ultraviolet light and abrasion.The pollution of microplastics in the environment has attracted worldwide attention.The two most important ways of human body being exposed to microplastics are respiratory tract and digestive tract.At present,there are many studies on digestive tract exposure,the exposure evaluation,toxic effects and mechanism of action in food and drink have been extensively reported.In contrast,there are few studies on respiratory exposure,especially the exposure evaluation of health hazard assessment which is the first step of assessment.The main reasons are as follows:The evaluation of exposure through the respiratory tract not only has difficulties as the external exposure is different between indoor and outdoor and can be influenced by many different factors,the evaluation of internal exposure also faces the difficulties of obtaining representative bronchoalveolar lavage fluid and lung tissue biopsy.Due to the epidemic of COVID-19,the use of masks remains high.There are studies showing that surgical masks are made of plastic,which can become another potential source of pollution of microplastics,and increase the risk of humans being exposed to microplastics while preventing the invasion of pathogenic microorganisms.But so far,the related exposure evaluation has not been reported.In this study,we took great advantages of the nasal lavage fluid and sputum as they can be used as good indicators of exposure load in the respiratory system.These samples are easy to collect and non-invasive,and can be carried out in large-scale population epidemiological investigations.We conducted a preliminary study of evaluating the load of microplastics in nasal lavage fluid and sputum in typical indoor and outdoor populations to clarify the feasibility of nasal lavage fluid and sputum as indicators of internal exposure by a combination of polarized light microscope and laser infrared imaging system.The qualitative and quantitative detection methods were verified in the lung tissues of domestic pigs in representative contaminated areas,and the accuracy of the detection method combined with polarized light microscope and laser infrared imaging system for different pollution levels was confirmed.On this basis,we made use of advantages as follows:the campus area of a university is relatively independent,the architectural style and materials are unified,the interior furnishings are consistent,the students’demographic characteristics are simple,the casas of respiratory system diseases are less,the life styles are relatively consistent,the compliance and cooperation degree are high,which means there are fewer interference factors in the evaluation of the external and internal exposure of microplastics in the air.We collected indoor and outdoor air samples from different functional zones on campus to evaluate the external exposure load of microplastics in the air,to clarify the level and characteristics of indoor and outdoor exposure and reveal the correlation between indoor and outdoor pollution of microplastics.Graduate students were recruited as the investigation objects to evaluate the internal exposure levels of microplastics through respiratory tract,intervention studies on different kinds of masks were conducted to reveal the levels and characteristics of microplastic pollution in human biological samples,to clarify the influencing factors,and confirm the influence of masks on human internal exposure.Methods:1.Taking couriers as the outdoor typical population,office workers as the indoor typical population,and the Institute of Preventive Medicine of China Medical University as the research site,a total of 8 office staff and 8 couriers within 3 km radius around the Institute of Preventive Medicine were recruited as the research objects.Nasal lavage fluid and sputum samples of the subjects were collected,and then divided into equal parts before digestion treatment.One of the samples was filtered through a membrane and made into a dual slide chamber,observed under Leica DM4B DFC7000T polarized light microscope and recorded its number,size and the shape of microplastics.The other one was concentrated by nitrogen blowing and put into the Agilent 8700 laser infrared imaging system to determine the main composition of microplastics.The student’s t test was used to analyze whether the difference in the abundance of microplastics in nasal lavage fluid and sputum of typical indoor and outdoor populations was statistically significant.The lung tissues of domestic pigs raised in typical contaminated areas for more than 1 year and fetal pigs that died of asphyxia before birth were taken as the research objects.Polarized light microscope and laser infrared imaging system were used to analyze the abundance and characteristics of microplastics in lung tissues of pigs and fetal pigs.2.A total of 39indoor and outdoor air dust fall samples were collected from different functional zones(living area,learning or work area and activity area)in the campus,including 18 indoor and 21 outdoor air dust fall samples.After digestion treatment,the microplastics were made into dual slide chambers,which were observed by polarizing light microscope to record the quantity,particle size and shape of microplastics.Part of samples were selected for detection by laser infrared imaging system to determine the distribution of microplastics in indoor and outdoor air dust fall.The student’s t test and ANOVA were used to analyze whether the differences in the abundance of microplastics in air dust fall in different places and whether the influences of different indoor factors on the abundance of microplastics in indoor air dust fall were statistically significant.Correlation analysis was used to clarify the relationship between the abundance of microplastics in indoor and outdoor air dust fall and temperature and humidity.Consistency test was used to analyze the homology of microplastic pollution in indoor and outdoor air dust fall.3.A total of 113graduate students were recruited to be investigated the internal exposure of respiratory microplastics on campus.Subjects were randomly divided into a natural exposure group(n=54),a surgical mask intervention group(n=29),and a cotton mask intervention group(n=30).Participants in the intervention group were asked to wear the masks for 3 days,no less than 2 hours per day.On the fourth day,they would finish the questionnaire and be collected nasal lavage fluid by professionals in the laboratory.The Mask Wearing Record sheet was retrieved at the same time.The nasal lavage fluid was digested and made into dual slide chambers,which were determined the number,size and shape of microplastics by polarizing light microscope.Part of samples were randomly selected from each group for the detection of microplastics components by Agilent 8700 laser infrared imaging system.The student’s t test or ANOVA were used to do the single factors analysis of the abundance of microplastics in nasal lavage fluid,the generalized linear model was used for multi-factor analysis and the Chi-square test was used to analyze the differences in the population characteristics of volunteers in each group and whether there were differences in the particle size,shape and composition distribution of microplastics in nasal lavage fluid in each group.ANOVA was used to analyze whether there was statistical significance in the abundance of microplastics in the nasal lavage fluid of volunteers in each group,and the influence factors were controlled by the generalized linear model to further clarify the influence of mask use on the abundance of microplastics in the nasal lavage fluid.Results:1.Couriers and office workers were regarded as typical outdoor and indoor populations,respectively.The abundance of microplastics in the nasal lavage fluid of couriers(0.76±1.51 MPs/g)was significantly lower than that of office workers(2.24±1.82MPs/g)(P<0.01).The shape of microplastics in the nasal lavage fluid of couriers and office workers was mainly fibrous,accounting for 83.81%and 87.03%respectively.PA(25.56%)and PE(23.06%)were the main microplastics in the nasal lavage fluid of couriers,while PVC(41.40%)and PA(31.81%)were the main microplastics in office workers.There was no significant difference in the abundance of microplastics in sputum between couriers(92.09±1.76 MPs/g)and office workers(58.55±3.33 MPs/g)(P=0.35).The microplastic shape in sputum of couriers(94.26%)and office workers(83.28%)was still mainly fibrous.PC(23.93%)and PVC(23.08%)were the main microplastics in the sputum of couriers,while PVC(40.21%)and PA(25.30%)were the main microplastics in the sputum of office workers.The abundance of microplastics in fetal pig lung tissue was 6 MPs/g,and that in domestic pig lung tissue was 12 MPs/g,both of which were fibrous.The main microplastics in fetal pig lung tissues were PC(32.99%),PP(15.46%)and PVC(15.46%),and PA(46.11%),PP(21.11%)and PE(17.22%)in the lung tissues of domestic pigs.2.In different functional zones on campus,the average abundance of microplastics in outdoor air dust fall was 1666.18 MPs/(d·m~2),and the difference among different functional zones was not statistically significant(P=0.78).Among them,the abundance of microplastics in outdoor air dust fall of teaching building was significantly higher than that of sports stadiums(P=0.13).The average abundance of microplastics in indoor air dust fall was2244.89 MPs/(d·m~2),of witch in the female dormitory was higher than that in office building(P=0.13)and library(P=0.12).And the abundance of microplastics of teaching building was higher than library(P<0.15).Humidity(P=0.03),curtains(P=0.10)and the use of air conditioner(P=0.03)were significantly correlated with the abundance of microplastics in indoor air dust fall.Different cleaning methods(P=0.42)and frequency(P=0.55)had no significant effect on the abundance of microplastics in indoor air dust fall.The comparison between indoor and outdoor air dust fall showed that the abundance of microplastics in indoor was higher than that in outdoor air dust fall,but it was not statistically significant(P=0.26).In both outdoor and indoor air dust fall,the main microplastic shape was fibrous,but the proportion of indoor fiber(94.06%)was significantly higher than that of outdoor(87.52%)(P<0.01).There were also significant differences between indoor and outdoor components(P<0.01).The main components were PA(34.45%)and PC(28.26%)in outdoors air dust fall,and PA(30.62%)and PE(33.33%)in indoors air dust fall.The particle size of microplastics in outdoor(53.87%)air dust fall mostly concentrated below 200μm,and in indoor(62.70%)air dust fall mostly concentrated below 500μm.The difference of particle size distribution was statistically significant(P<0.01).3.Under natural conditions,the abundance of microplastics in human nasal lavage fluid was 31.90±1.77 MPs/g.The multi-factor generalized linear model analysis showed that office air conditioning usage within 3 days(Occasionally used vs None/Not used:β=0.24,P=0.09;Frequently used vs None/Not used:β=-0.17,P=0.22)and towel material(Without chemical fiber vs Containing chemical fiber:β=0.24,P=0.08)were significantly correlated with the abundance of microplastics in nasal lavage fluid.In the natural exposure group,main shape of the microplastics was fibrous(88.06%),and the main components were PA(43.70%),PC(13.80%)and PE(12.83%).Compared with the natural exposure group,after controlling for other influencing factors,the abundance of microplastics in nasal lavage fluid in surgical mask intervention group was significantly higher than that in natural exposure group(β=0.25,P=0.01).The abundance of microplastics in nasal lavage fluid was slightly lower in the cotton mask intervention group than in the natural exposure group,but the difference was not statistically significant(β=-0.11,P=0.23).The shape of microplastics in nasal lavage fluid of volunteers in surgical mask intervention group(92.01%)and cotton mask intervention group(89.38%)was mainly fibrous.There was significant difference in the shape of microplastics in nasal lavage fluid between all groups(P<0.01).Also,the main components of microplastics in nasal lavage fluid were different(P<0.01).In the surgical mask intervention group,the main microplastics were PC(25.30%),PA(24.10%)and PVC(19.28%),while in the cotton mask intervention group were mainly PA(28.32%),PC(25.66%)and PE(15.04%).The particle size of microplastics in natural exposure group(59.30%),surgical mask intervention group(64.57%)and cotton mask intervention group(58.50%)were mostly less than 200μm,and the difference of particle size distribution was statistically significant(P<0.01).Conclusion:1.The presence of microplastics was detected in nasal lavage fluid and sputum of typical indoor and outdoor population,and the indoor exposure level was higher than that of outdoor population,mainly fibrous.2.The combination of polarized light microscope and laser infrared imaging system could effectively detect the exposure status of microplastics in biological samples.3.The pollution levels,particle size and main components of microplastics in indoor and outdoor air dust fall were different,but they were mainly fibrous,and the indoor exposure load was higher than that of outdoor air.Microplastic pollution in indoor and outdoor air has non-homology.4.Under natural exposure condition,the abundance of microplastics in human nasal lavage fluid was31.90±1.77 MPs/g,mainly fibrous,with PA,PC and PE as the main components.Individual behavior was the main factor affecting respiratory microplastic exposure.Masks of different materials could significantly affect the microplastic exposure level of human respiratory tract.Wearing surgical mask could significantly increase the level of microplastic exposure in nasal lavage fluid. |
PDF Full Text Request