| Microplastics(MPs)are pervasive in the environment and have posed growing threat to ecosystems and human health.Nowdays,the composition and migration mechanism of microplastics in river and lake systems in plain area have been widely studied,yet the composition and variation of microplastics in high-altitude basins such as river headwaters are were not well understood.This study was based on 152 samples collected from surface water(freshwater lakes,salt lakes,urban rivers,rural rivers and agricultural channels,etc.),sediments and soil samples(mulched farmland,greenhouse farmland,open farmland,grassland)at the typical river basins in the Tibetan Plateau region.The abundance,composition,source,migration and transformation mechanism of microplastics in water and soil of the Qinghai-Tibet Plateau(QTP)were analyzed.For water,MPs were detected in 97 out of 100 water samples with the range from 66.7～2000 particles m-3(average 584.82 particles m-3),and the higher concentration of MPs near cities and large lakes related to human activities.There was a significant difference in mean MP levels among different water bodies(p>0.05),in a descending order of:turbid rivers>agricultural channel water>lakes>ordinary rivers;Brine lake>saltwater lake>freshwater lake(according to salinity).Fibers were the most frequently observed shape in the water with the particle sizes mostly ranged from 100 to 500 μm,and the greatest number of polymers was polypropylene.The main conclusions of water bodies include:(1)Source analysis identified the major sources of MPs in the QTP were domestic wastewater and tourism in some areas(scenic spots).In addition,other source of MPs in water was agricultural activities(southwest of the QTP)and atmospheric transmission.(2)The analysis results of water quality parameters and MP concentrations showed that MP abundance was associated with the water quality(especially COD)on the QTP,and it was negatively correlated with altitude due to less human activities(especially agricultural activities)at high altitude areas.Besides,more abundant MPs with small sized was found in the higher altitudes than low ones.(3)The proportion of small MPs(20-100 μm)increased with the enhancement of ions concentration,indicating that MPs degradation might occur more rapidly under high ions(especially cations)concentration.Ions may affect MPs fragmentation rate by means of surface intrusion in water,and high ions concentration associated with intense surface erosion on MPs.(4)Spatially,the obviously spatial trend was that MP abundance increased at downstream of the Yarlung Zangbo River,which was due to the higher population density in the downstream contributing to more plastic waste inputs,and MPs from tributaries flowing into the river cannot be ignored(especially from the first major tributary i.e.,Lhasa River).(5)The total amount of microplastics in Yarlung Zangbo River was estimated and simulated based on In VEST model,which showed that the annual average amount of microplastics discharged from the exports of the Yarlung Zangbo River basin was 994.60 tons.Among them,the area with the highest annual output of microplastics in Yarlung Zangbo River Basin was located in downtown of the Lhasa,with the output of 20.72kg/km2,which was equivalent to about 1151 of 550mL mineral water bottles per square kilometer yearly.For sedimemnt:MPs were found in sediment samples with mean abundance being 41.52 ± 22.31 items/kg,ranging from 10-90 items/kg.The most common characteristics of MPs were similar between in water and sediment.A similar MP abundance distribution pattern within different types of water bodies was also found in sediments,while there was no significant difference in lake sediment with different salinity.For soil:MPs were detected in 49 of the 52 soil samples.(1)The MP concentration was ranging from 0 to 260 items/kg(lower than most areas studied),and the average numbers of MPs were(53.2 ± 29.7)items/kg and(43.9 ± 22.3)items/kg in shallow(0～3cm)and deep soil(3～6cm),respectively.(2)A descending order of MP abundances was observed among different land use types:mulch farmland,greenhouses,farmland without covering,and grassland.(3)The MPs were mostly in the form of a film and transparent in color in this study.The dominant polymers of MP s in the soil samples were polyester(PE)and polypropylene(PP).(4)MPs may stem from the fragmentation of plastic mulch in farmland soil,and other source includes plastic packaging discarded.(5)MP abundance increased with the increase in mulching time in facility agriculture.Additionally,the proportion of small MPs(<500 μm)in facility agriculture were higher than those in bare farmlands and grasslands,and human disturbances and increased mulching time in facility agriculture promote the fragmentation of soil MPs.This study provides data and theoretical bases for analyzing MPs migration and degradation processes in high altitudes.A long-term monitoring of MPs in the water and soil environments of QTP should be considered in further investigation,which is significant on understanding the fate of MPs in the Plateau environment. |
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