Characteristics Of Residual Film Pollution In Farmland And Toxicity Effects Of Polyethylene Microplastics To Aquatic Animal In China

Mulching can increase crop yield and improve the quality of agricultural products,and has various functions such as water-saving,warming,inhibiting grass and weeds,salt inhibition and seedling protection,and increasing scattered light.However,due to the difficulty and high cost of plastic film recycling,it is easy to residual and accumulate microplastics in farmland soil,causing certain harm to the soil environment.Over the past decade,the promotion and use of plastic film have made significant contributions to improving agricultural quality and efficiency,but the residual plastic film and the accumulation of microplastics have had a serious impact on soil and water bodies.At present,the pollution characteristics and soil water environmental effects of plastic film residues in China have not been systematically studied.This study is based on micro survey data from 2025 households in 5 provinces of China,introducing formal and informal systems into the analytical framework to analyze farmers’awareness of agricultural film pollution and the factors affecting farmers’awareness;Taking long-term film covered soil of 54 samples from 29 provinces in China as the research object,this study reveals the distribution characteristics of soil microplastics in farmland soil,and elucidates the relationship between the distribution of film residue and the methods of film recovery,film coverage years,soil texture,and film covered crops;Taking Brachionus calyciflorus and zebrafish as model organism,along with high-throughput sequencing and transcriptomic sequencing as detecting method,the toxic effects of microplastics on aquatic organisms after diffusion into water were studied to reveal the toxic mechanism of microplastics on aquatic organisms.The main results of the study are as follows:（1）Nowadays,the agricultural production of China is mainly focused on small-scale farmers,with the characteristics of large quantity,small scale,and dispersion.Small farmers play vital role to preventing and controlling agricultural film pollution.A survey conducted on2025 households from 5 provinces in China found that 53.78%,33.98%and 12.25%of farmers respectively believed agricultural mulch film would cause pollution to farmland,would not cause pollution,and did not know whether there was pollution.Attitude,subjective norms,perceived behavioral control,and family characteristics are all important factors that affect farmers’cognition.Compared with formal systems,village regulations and agreements,as an informal system,play an important role in promoting the recycling and utilization of agricultural film.Corresponding measures can be taken to improve the overall cognitive level of farmers.（2）The plastic residues in film-covered soil in China were mainly polyethylene（PE）and polypropylene（PP）.The average abundance of microplastics and medium plastics were213 and 10 items kg^-1,respectively.The main forms of micro（medium）plastic were film,fragment and fiber,95.35%of that was less than 5 mm,and 39.70%of that was less than 1mm.The color was mainly blue,followed by white and yellow.The years of plastic film mulching,soil texture and types of plastic film mulching crops will also affect the content of soil microplastics.（3）Polyethylene microplastics have toxic effects on zooplankton（Brachionus calyciflorus）.Brachionus calyciflorus could ingest microplastics in 10～22μm from water environment,and increased the intake of microplastics with the decrease of the density of the feeding algae.Increasing algal food supplyment could effectively mitigate toxic effection of polyethylene microplastics on rotifers.Under limited food supplement conditions,exposure from microplastics reduced the swimming line speed of rotifers,accompany with increasing SOD activity and Na⁺-K⁺-ATPase enzyme activity and decreaseing GPx activity of rotifers.（4）Polyethylene microplastics also have toxic effections on zebrafish,mainly manifested in increasing the respiratory rate of zebrafish,producing oxidative stress and neurotoxicity.Polyethylene microplastics also can change the expression of genes related to immune and metabolic pathways in the intestine and gills of zebrafish,as well as the composition and proportion of certain phyla and taxonomic level flora,except changing the core microflora structure of zebrafish intestinal microorganisms.By affecting Fox O signaling pathway,cell senescence,p53 signaling pathway and circadian rhythm pathway,it causes cell cycle arrest,cell loss and apoptosis,and induces oxidative stress in zebrafish.It reveals increasing exposure time and particle size of microplastics lead to the accumulation of toxicity and damage to aquatic organisms.This study conducts micro surveys of farmers and long-term monitoring of agricultural film pollutants nationwide,analyzes farmers’understanding of agricultural film pollution and its influencing factors,reveals the distribution characteristics of residual soil microplastics and their toxic effects on aquatic organisms.The research results provide theoretical support for the prevention and control of mulch film residual pollution as well as scientific basis for the formulation of relevant policies.