A Study On Characterization Of Microplastic Pollution In Mulched Arable Land In Guizhou And The Growth Stress Of Microplastics On Tobacco(Nicotiana Tabacum L.)

Microplastics are a new type of pollutant with stable nature,wide distribution and easy diffusion and migration,which has received extensive attention from scholars worldwide in recent years.Existing studies have confirmed that microplastics are ubiquitous and persistent pollutants.Microplastics have been detected in environmental media such as water,atmosphere,and soil.Microplastics are highly reactive and migratory,and can be absorbed into the body by organisms,resulting in biotoxicity.Terrestrial ecosystems still lacked in-depth studies,and there were fewer studies on the characteristics of microplastics in different soil environments,and the physiological toxicity of microplastics to plants.To this end,this study was conducted in Guizhou Province to analyze the characteristics of microplastics in the soil environment by taking the mulched arable land as the object of investigation.The effects of microplastics on the growth and physiological characteristics of tobacco were also investigated by using laboratory simulations.The main findings were as follows:In this study,we evaluated the extraction method of microplastics（LDPE）from mulched arable land mulch source,using waste mulch to prepare standard microplastics,considering the effect of microplastic（LDPE）particle size and concentration,the recovery rate of microplastics,and the removal rate of organic matter to determine the feasibility and superiority of the method of NaCl solution separation and ablation with30%H₂O₂ at 50℃.The recovery rate of microplastics by this method was 70%～100%,and the removal rate of organic matter was up to 96%.The material observed after the ablation was clearly discernible,and the morphological characteristics of microplastics were almost unaffected.Microplastics were found in all samples of mulched arable land in Guizhou Province,with microplastic content ranging from 143.28 to 3283.46 item/kg,with an average content of 1150.60±647.86 item/kg.The maximum average microplastic content was 469.63±437.43 item/kg at GD sampling site and the minimum average microplastic content was 1835.75±973.00 item/kg at QXG sampling site./The highest percentage of detected microplastics was 64.79%in the particle size of 10-100μm,and the lowest percentage was 0.19%in the particle size of less than 1μm.The microplastics existed in the form of fragments,and their colors showed black,transparent and translucent.The surface of the fragmented microplastics is rough,with erosion evident,forming grooves,pits and holes,irregularly shaped edges,and with particles adhering to the surface.Under the influence of environmental factors such as UV radiation,the microplastic morphology showed different degrees of aging.The polyethylene in fragments form may mainly originate from agricultural films used in agricultural production.The highest average microplastic content was found in the mulching years of 17-21 years,reaching 1693.47±1107.45 item/kg,and the mulching years were extremely significantly and positively correlated with the microplastic content（P<0.05）.The highest average microplastic content was 1462.63±274.79item/kg for potatoes,1247.16±609.06 item/kg for no irrigation,and 1347.88±1054.39item/kg for clay soils.Mulching is the main source of soil pollution in arable land,and continuous mulching significantly increases the accumulation of microplastics in arable land and aggravates the degree of microplastic pollution.Studies on tobacco exposed to microplastics showed that root length,root volume,root projected area,and root tip number were negatively correlated with microplastic concentration（0 mg/L,10 mg/L,100 mg/L,1000 mg/L）,which indicates that polyethylene（13μm particle size）microplastics were able to affect the root conformation of the tobacco plant and significantly inhibit root growth and development.In addition,plant height,stem circumference,and maximum leaf area were also negatively correlated with microplastic concentration,which indicated that microplastics had a significant negative effect on the growth characteristics of tobacco plants.The stress effect of microplastics also had a significant limitation on the accumulation of tobacco plant biomass,and there was a（highly）significant correlation between above-ground and root fresh matter mass and microplastic concentration,especially at high concentration treatments,where both above-ground and root fresh matter mass were highly significantly different from the CK treatment.Polyethylene microplastics had less effect on chlorophyll of tobacco leaves,but produced some oxidative damage to tobacco leaves,increased MDA content,and fluctuations in antioxidant enzymes to synergistically scavenge ROS,where SOD content was elevated in all treatments of microplastic stress,POD was consumed in the medium and low concentration treatments,and CAT was consumed to scavenge ROS in the high concentration treatment.polyethylene microplastics altered the physiological characteristics of tobacco,causing tobacco to develop traits that resist unfavorable environments during growth and interfere with tobacco biomass accumulation.This study provided data and a theoretical basis for the characteristics of microplastic and the biotoxicity of microplastics to tobacco in mulched arable land in Guizhou,and more in-depth studies on the effects of microplastic production are still needed in the future.