Ecotoxicological effects of different size ranges of industrial-grade polyethylene and polypropylene microplastics on earthworms Eisenia fetida

Highlights: • HDPE and PP MPs with different size ranges can be ingested by E. fetida. • HDPE and PP MPs exposure can induce size-dependent oxidative stress in E. fetida. • The oxidative stress induced by PP MPs was higher than that induced by HDPE MPs. • Pathways involved in neurodegeneration, oxidative stress and inflammation altered. The effects of microplastics (MPs) on terrestrial organisms remain poorly understood, even though soil is an important MPs sink. In this study, the earthworms Eisenia fetida were exposed to 0.25% (w/w) of industrial-grade high-density polyethylene (HDPE, 28–145, 133–415 and 400–1464 μm) and polypropylene (PP, 8–125, 71–383 and 761–1660 μm) MPs in an agricultural soil for 28 d. The results showed that HDPE and PP MPs with different size ranges can be ingested by E. fetida. Exposure to different size ranges of HDPE and PP MPs altered the activities of superoxide dismutase, catalase and glutathione S-transferase and induced an increase in the 8-hydroxy-2′-deoxyguanosine level in E. fetida, suggesting that MPs-induced oxidative stress occurred in E. fetida. A size and type-dependent toxicity of MPs to E. fetida was demonstrated by the integrated biological response index. In addition, to obtain detailed molecular information on the responses of E. fetida to MPs exposure, transcriptomic analysis was conducted for E. fetida from HDPE (28–145 μm) and PP (8–125 μm) treatment groups. Transcriptomic analysis identified 34,937 and 28,494 differentially expressed genes in the HDPE and PP MPs treatments compared with the control, respectively. And, exposure to HDPE and PP MPs significantly disturbed several pathways closely related to neurodegeneration, oxidative stress and inflammatory responses in E. fetida. This study provides important information for the ecological risk assessment of different size ranges and types of industrial-grade MPs.