Distribution Characteristics Of Microplastics In Farmland Soil Around Shenyang

Microplastics(MPs)are diameters less than 5 mm plastic particles,in recent years it has become a new type of pollutants in the global environment concern.Due to its small size,large specific surface area,easy adsorption,difficult degradation and toxicity,it affects the migration and transformation of all kinds of pollutants in the environmental system and causes harm to human health.The spatial distribution and toxicological effects of MPs in water environment have been studied extensively,but due to the difficulty of separating and extracting MPs from soil,MPs in soil have not been further studied.In this study,the farmland soil around Shenyang,a typical city in the old industrial base of Northeast China,was taken as the research object.A total of84 soil samples were collected from four areas in the east,west,south and north of Shenyang,and the soil layers(5-10 cm,10-20 cm and 20-30 cm)in five soil profiles were analyzed by means of sample plot investigation method.By density separation flotation and optical microscope identification,and connecting with the pyrolysis gas chromatography/mass spectrometry(Py-GC/MS)to form the soil MPs identification and qualitative analysis,quantitative the morphological characteristics of MPs in farmland soil around Shenyang,material composition and the characteristics of the spatial distribution and through correlation analysis method and PMF model method,reveals the basic soil physical and chemical properties of soil MPs and the influence of the main source of MPs.The main conclusions are as follows:(1)MPs are commonly found in farmland soils around Shenyang,and their physical forms are mainly thin film,fragmental,fibrous and granular.The main MPs were PE microplastics(polyethylene),PP microplastics(polypropylene)and PS microplastics(polystyrene),and the detection rates were 81.40%,54.15% and 52.60%,respectively.No other kinds of MPs were detected.The total concentration of soil MPs ranged from 217.30 μg/g to 2512.18 μg/g,the mean value was 1327.69 μg/g.The composition characteristics of soil MPs were PE > PP >PS,and the average content of PE was 760.03 μg/g,which was 2.03 and 3.93 times of that of PP and PS,respectively.(2)The content of MPs in farmland soil varies greatly in different areas.In the western part of Shenyang,the concentration of MPs was the highest,the mean value was 1569.59 μg/g,followed by the eastern part and the northern part,the mean values were 1320.28 μg/g and 1217.56 μg/g,respectively.In the southern soil,the concentration of MPs was the lowest,with an average of 1208.85 μg/g.The soil MPs concentration in different regions was PE > PP >PS,but the content of PP in the eastern region was relatively high,and the content of PS in the northern region was relatively high.(3)Different planting patterns had effects on soil MPs concentration.PE > PP >PS was found in both greenhouse and ground soil in different areas,but the average value of MPs in greenhouse soil was 1439.56 μg/g,1.21 times of that in the ground,and the concentration of PS in soil in the ground was higher than that in greenhouse soil.Among the greenhouse soils planted with lettuce,kidney bean,watermelon field,green onion and corn,the content of MPs in the soil of lettuce field was the highest(1947.61 μg/g),and the content of MPs in the soil of watermelon field was the lowest(641.29 μg/g).(4)The soil MPs concentration decreased significantly from the surface to the ground,from 998.76 μg/g in the surface soil(0～5 cm)to 193.00 μg/g in the deep soil(20～30 cm).The decrease of soil MPs concentration was the largest under kidney bean planting(90.46%),while the decrease of soil microplastics concentration was the least in corn field(68.77%).(5)Soil p H value,moisture content,organic matter and electrical conductivity had significant effects on the distribution of soil MPs.Soil PE microplastics were observably negatively correlated with soil p H and water content,and negatively correlated with electrical conductivity.There was a significant negative correlation between PP microplastics and soil p H value and water content.PS microplastics had significant negative correlation with soil organic matter and p H value.(6)The source analysis of soil MPs in farmland around Shenyang was carried out by using PMF model,the results show that the soil MPs in farmland around Shenyang,mainly from the use of agricultural plastic film,atmospheric micro plastic settlement and fertilizer,secondly from plastic garbage landfill soil and land utilization of sewage sludge,the contribution of various sources of MPs are 24.2%,23.1% and 21.1%respectively,and 19.4% and 12.2%.