Toxicity comparison of multiple biodegradable and conventional microplastics on earthworms: Ingestion, tissue damage, oxidative stress, and transcriptional responses

Although the environmental risks pose by biodegradable microplastics (BMPs) have drawn increasing attention, the differences in toxicity and underlying mechanisms between BMPs and conventional microplastics (CMPs) toward soil organisms remain unclear. Furthermore, comparative safety assessments of various types of BMPs lack comprehensive multidimensional data support. This study systematically compared the toxic effects and mechanisms of action of four representative BMPs (polylactic acid, polycaprolactone, poly(butylene succinate), and poly (butyleneadipate-co-terephthalate) and one mainstream CMPs (polyethylene, PE) through a comprehensive multi-faceted analysis. The study was performed at concentrations of 0.25 %, 0.5 %, and 1 % (w/w), using earthworms (Eisenia fetida) as the test organism, and employed multi-faceted analyses, including ingestion, oxidative stress, tissue damage, and transcriptomic responses. These results indicated that BMPs were more readily ingested by earthworms and subsequently fragmented compared to PE microplastics. Different types of microplastics affected different parts of the earthworm's epidermis and intestinal tissues, resulting in varying degrees of damage. Exposure to different types of microplastics induced oxidative stress in earthworms, which was closely related to the microplastics type, exposure concentration, and duration. At the transcriptional level, both BMPs and PE microplastics exposure affected pathways linked to carbohydrate, protein and lipid synthesis, inflammatory and immune responses, energy metabolism, and cellular homeostasis in earthworms, whereas BMPs exposure also significantly influenced pathways associated with apoptosis. Overall, the toxicity of BMPs to earthworms was comparable to or higher than that of PE microplastics. Our results provide novel insights into the ecological risk assessment of BMPs in terrestrial ecosystems.