Polylactic acid microplastics induce higher biotoxicity of decabromodiphenyl ethane on earthworms (Eisenia fetida) compared to polyethylene and polypropylene microplastics

Decabromodiphenyl ethane (DBDPE) and microplastics (MPs), such as fossil-based polymers polyethylene (PE), polypropylene (PP), and bio-based plastics polylactic acid (PLA) are abundant in e-waste dismantling areas. However, the information on the effects of DBDPE combined with MPs (DBDPE-MPs) on earthworms is still limited. In this study, we explored the impacts of DBDPE-MPs on neurotoxic biomarkers, tissue damage, and transcriptomics of Eisenia fetida by simulating different exposure patterns of 10 mg kg-1 DBDPE and 10 mg kg-1 DBDPE-MPs (PLA, PP, and PE). Results showed that the activities of acetylcholinesterase, Na+/K+-ATPase, Ca2+/Mg2+-ATPase, carboxylate enzyme, and the contents of calcium and glutamate were significantly stimulated. DBDPE-MP co-exposure caused more severe damage to the epidermis, muscles, and tissues. Transcriptomic analysis revealed that differentially expressed genes (DEGs) of DBDPE-MPs were mainly related to inflammation, the immune system, digestive system, endocrine system, and metabolism. DBDPE and PP-MPs had similar influences on immunity and metabolism. However, DBDPE-PLA and DBDPE-PE further affected the endocrine system and signaling pathways. Specific DEGs showed that detoxification systems in the case of MPs were significantly upregulated. The study indicated that MPs exacerbated DBDPE toxicity in the nervous system, epidermis, and gene regulation of E. fetida, helping to assess the ecological risks of e-wastes and microplastics in soil.