| The pollution characteristics of environmental microplastics(MPs,size<5 mm)is one of the hot directions of the current international researches on MPs worldwide.Numerous field investigations have shown that MPs are widely distributed in water,soil,and organisms.In comparision,the pollution characteristic of MPs in the air has been rarely reported,partly due to the relatively immature investigation method.The air quality of human settlemnets is closely related to human survival and health.Therefore,the research on the investigation method and pollution characteristics of atmospheric MPs in human settlements is of great significance to enrich the investigation data and clarify the potential human health risks of MPs.In the present study,we selected a university in Shanghai as a typical representative of human settlements and carried out long-term monitoring of MPs in the air.Combined with airflow disturbance simulation experiment and molecular biology approaches,we explored the pollution characteristics,sources,influencing factors,and the possibility of MPs as a potential carrier of human pathogens.At the same time,we evaluated human exposure level to MPs via atmospheric fallouts.The main research contents and results are as follows:(1)The investigation and analysis menthod of MPs in the air of human settlements was established.Five monitoring sites including three indoor and two outdoor ones were selected.MPs in the air were collcted by both active and passive sampling methods and identified by?-FTIR,?-Raman,and Nile red staining.The results showed that under the microscope(80×),approximately 40%of the suspected MPs collected by active sampling method were<50?m.Due to the limitation of picking particles under the microscope and the detection limit of?-FTIR(20?m),these particles cannot be identified.Due to the fluorescence/additive interference and sample burning,these particles cannot be identified via?-Raman(detection limit=500 nm).Meanwhile,due to the weak selectivity,these particles cannot be identified by Nile red staining either.In comparison,more than 99%of the suspected MPs collected by passive sampling method were>50?m,which could be identified and quantified via?-FTIR and microscope.The passive sampling method(CV value of the replicates<20%)combined with?-FTIR had the advantages of strong feasibility,low time and economic cost,simple operation,and slight MP lost/contamination.Through the optimization experiments,it was determined that the duration of single sampling was 24 h and the open area of the sampling container was?0.125 m~2.(2)MPs in atmospheric fallout of the campus were characerized.A school gate and an open ground were selected as outdoor sampling sites and monitored for ten months.The results showed that the MP abundance ranged from 25 to 5.5×10~3 MPs/m~2/d,showing obvious spatial difference and temporal fluctuation(seasons).MP abundance of the school gate(2.1×10~3 MPs/m~2/d)was significantly higher than that of the open groud(0.6×10~3MPs/m~2/d).The shape of the MPs was mainly fiber(90.8%);other shapes included fragment,film,and foam.Their colors were mainly transparent(58.8–62.5%)and blue(28.4–30.4%).The MP sizes were concentrated in 100–2000?m.The polymer types were mainly polyester and rayon,the sum abundances of which accounted for>70%.A student dormitory,an office,and a corridor were selected as indoor sampling sites and monitored for three months.The results showed that the MP abundance ranged from 476.9 to 23348.4 MPs/m~2/d,showing obvious spatial difference and temporal fluctuation(weekday and weekend).The highest MP abundance appeared in the dormitory(9912±7033 MPs/m~2/d),followed by the office(1848±1164 MPs/m~2/d),and the corridor(1459±1045 MPs/m~2/d).The MP sizes were concentrated in 100–2000?m.The polymer types were mainly polyester and rayon,the sum abundances of which accounted for>90%.The MPs mainly originated from textiles,which also released large amounts of natural microfibers.The airflow disturbance simulation experiment showed that airflow disturbance can lead to resuspension and migration of the deposited MPs,the higer wind speed,the stronger resuspension effects.Meteorological factors(e.g.typhoon and airflow disturbance)and human acivities(intensity)are the main factors affecting the abundance and spatiotemporal distribution of MPs in atmospheric fallout.(3)MP fallout in dining environments was investigated and the potential human intake was estimated.The results showed that in the 42 dining spots,all MPs were fibrous(i.e.plastic microfibers).Plastic microfibers and natural microfibers were collectively called micrcofibers(MFs).MF abundance of the restaurants during the peak hour of dinnertime(75±19 MFs/plate/meal)was approximately two times that of the households(36±23MFs/plate/meal).The high MF abundance was positively correlated with strong human activities(i.e.,sitting rate of people)in restaurants,which was confirmed again by the kinetics data of the cafeteria(p=0.000).Additionally,the MF transport experiment in a bachelor flat and a condominium showed that room structure can obviously influence MF abundance that households without separate dining rooms(bachelor flat)showed three times higher MF abundance(66 MFs/plate/meal)than those(21 MFs/plate/meal)with separate dining rooms(condominium),because partition walls were verified to effectively reduce MF transport from other functional areas to the dining table.It is conservatively estimated that each person may ingest 63–232 MFs during meals per day,and the MPs therin was 18–75MPs.Through the friction simulation experiments by adopting fabrics of different materials and parameters,we found that cloth friction can aggravate MF shedding significantly.The amount of shedding MFs was affected by parameters of fabrics(e.g.hairiness)rather than materials.High hairiness and short staple yarn style were likely to increase the formation of MFs.(4)Potential human pathogens on MFs in indoor atmospheric fallout were characterized.Through 16S high-throughput sequencing,we found that the main bacterial phylums included Proteobacteria,Actinobacteria,Firmicutes,and Cyanobacterium.The gender of residents was likely to influence the bacterial community on MFs.The bacteria on plastic MF dominated samples and natural MF dominated samples were similar in bacterial diversity but differed in community structure;the abundance of genes related to human pathogen was higher in the former than the later.Six potential human pathogen species were found,including A.baumannii,A.johnsonii,B.anthracis,C.perfringens,H.influenzae,and S.pyogenes.The indoor bacterial growth simulation experiment showed that there was no significant difference in bacterial diversity and structure between natural and plastic MFs,indicating that both plastic and natural MFs in indoor atmospheric fallout may be potencial carriers of human pathogens.In conclusion,we developed a qualitative and quantitative investigation and analysis method for MPs in atmospheric fallout of human stellements referring to the traditional monitoring methods of atmospheric particulate pollutants.This enriches the pollution characteristic data of MPs in the air,improves our understanding of the characteristics,source,and influence factors of MPs in human settlements,reveals the possibility of MPs in the air as carriers of human pathogens,provides an important basis for evaluating the comphrehensive human exposure to MPs,and provides data for the formulation of MP related control measures and laws. |
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