Study On Intestinal Stress Responseto Polystyrene Microplastics In Eisenia Fetida

In the natural environment,some plastics are degraded into MPs by natural forces.Microplastics are plastic particles with particle size less than 5 mm.They are characterized by small diameter,large specific surface area,light texture and easy transfer.Microplastics exist and spread widely in the environment,especially in soil ecosystems where large accumulations have been found.Earthworms play an important role in soil as ecosystem engineers.It is often used to assess the risk of pollutants to soil ecosystems because of its high reproductive rate,strong adaptability and ability to feedback soil health.In this study,Eisenia fetida was used as the model organism to design microplastics with different sizes and concentrations,establish toxicity evaluation models,analyze the effects of polystyrene microplastics on the growth,development and survival rate of earthworm,and measure MDA content and catalase CAT activity in earthworm tissues.The damage degree of intestinal tissue of earthworm was analyzed by histopathology,and the diversity of intestinal microbiota and the changes of metabolites were further analyzed by 16S rRNA and non-targeted metabolomics technology.The toxicity effects of polystyrene microplastics exposed to earthworms with different particle sizes and concentrations were analyzed by variance analysis,correlation analysis and principal coordinate analysis,and the toxic responses of large soil animals to microplastics in soil ecosystems were revealed at the molecular level,providing a theoretical basis for the environmental health and ecological risks of microplastics.The results show that:(1)With prolonged exposure time of polystyrene microplastics,the body weight of earthworms increased gradually and was significantly higher than that of the control group,indicating that exposure to microplastics could promote the body weight of earthworms.The main reason may be the hormone effect caused by MPs,indicating that the exposure of polystyrene microplastics has an effect on the growth and development of earthworm.(2)Under the same concentration(250 mg/kg)of PS-MPs with different particle sizes,large microplastics(250μm)could significantly reduce the survival rate of earthworm and cause serious mechanical damage to intestinal tissues.It may be because microplastics with large particle size can produce stronger physical wear in intestinal tissues and form inflammation,which directly leads to the death of earthworms.(3)The α-diversity of intestinal bacterial community of earthworm exposed to microplastics of different sizes was significantly different from that of control group.Both Shannon and Simpson indices showed that the intestinal microflora of earthworms treated with microplastics was significantly higher than that of the control group,and the increase was more obvious under the exposure of 50 nm and 200 nm microplastics.β-diversity analysis showed that exposure to microplastics had a significant effect on the intestinal microbial community structure of earthworms.Proteobacteria,as the dominant microorganism in intestinal inflammation,was significantly higher in 250 μm-100 mg/kg and 250 μm-200 mg/kg treatment groups than the control group.This indicated that there was inflammation in the intestines of earthworms in the treatment group,which was consistent with the results obtained in Result(2).(4)Exposure to microplastics can significantly affect the metabolites in earthworms,which mainly belong to benzene and substituted derivatives,heterocyclic compounds and some amino acids.In particular,exposure to 50 nm and 200 nm microplastics significantly reduced the content of some amino acids on the TCA cycle in the host.Based on the above,the exposure of microplastics to Eisenia fetida,such a large soil animal,can affect the growth and development of earthworms,cause damage to the intestinal tissue structure of earthworms,significantly affect the intestinal microflora of earthworms and may cause metabolic disorders in earthworms.Therefore,attention to environmental health,especially the biotoxicity and ecological risks posed by emerging pollutants such as microplastics,should receive further attention.