| Microplastics are a new sort of environmental pollutant since they are difficult to breakdown further.They are small in size and large in number,and extensively spread in biological systems such as oceans,lakes,and soils.Current studies have primarily focused on aquatic bodies,with little research on soil microplastic pollution,and most of these studies on soil microplastics have likewise concentrated on agricultural fields.In this study,86 samples were collected from forest,dryland farmland(including open-air without mulching,greenhouse without mulching,open-air with mulching,and greenhouse with mulching),plantation(including organic fertilizer application and without organic fertilizer application),and urban road greenbelt(including provincial capital and prefectural cities,county cities,and township cities)from 11 prefectures and 24 counties in Yunnan Province.Then we tested and analyzed microplastic abundance,size,shape,color,and polymer type.The following findings were reached.(1)The amount of microplastic contamination rose as the number of years spent mulching increased.The open mulched soil accumulation rate in the 0-5 cm soil layer was 256.45 items/m~2(kg.a).The accumulation rate in the 5-10 cm soil layer was 234.23items/m~2(kg.a).Microplastic abundance was considerably higher in agricultural soils with open mulching than without mulching(P<0.05),whereas there was no significant difference between mulched and unmulched samples in greenhouses(P>0.05).Mulching was not a major source of microplastic contamination in greenhouses,while fertiliser bags and packaging were the main sources of contamination.Microplastic pollution in greenhouses and open-air agriculture with the same number of years of mulching:greenhouses with mulching>greenhouses without mulching>open-air with mulching>open-air without mulching.(2)Between the 0-5 cm and 5-10 cm layers,there was no significant difference in the size of the soil microplastics(P>0.05).Microplastics smaller than 0.5 mm were the most common,accounting for 54.8%-72.6%,0.5 mm-1 mm for 17.1%-22.5%,1 mm-2mm for 6.5%-14.5%,and 2 mm-5 mm for 2.5%-6.5%.(3)Microplastics in the soil samples included fragments,films,fibers and pellets,with no difference between the two soil layers.Microplastics were transparent,translucent,white,red,and black in color,with 38.7%-45.0%being fragments and 24.3%-31.5%being films.The most common polymer kinds were PP and PE,which accounted for 44%and 29%of the total,respectively.Agricultural film is the primary source of microplastic pollution in open fields,while irrigation water and plastic waste,in addition to agricultural film,is a major source of microplastic pollution in greenhouses.Organic fertilizer application was a substantial source of microplastic contamination in plantation soils,with microplastic concentrations significantly higher in soils with long-term organic fertilizer application than in soils without organic fertilizer application(P<0.05).(4)Microplastics were found in all soil samples tested in this investigation,including forest near highways and forest near farms.Microplastics were significantly more abundant(P<0.05)in urban road greenery and plantations than in dryland farmland,and significantly more abundant(P<0.05)in dryland farming than in forest land.The soils of the road green spaces were all contaminated to varied degrees with microplastics,with soil microplastic abundances ranging from 350-15800 items/kg.There was no significant difference between provincial capital cities and county cities(P>0.05),and all were significantly higher than township-level cities(P<0.05).Microplastic pollution is caused by sewage irrigation in green regions,vast volumes of plastic bags wrapped around fruits in plantation orchards,agricultural films in cultivated areas,organic fertilizer,and packaging in big,cultivated areas. |
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