Microplastic digestion generates fragmented nanoplastics in soils and damages earthworm spermatogenesis and coelomocyte viability

Despite concerns about the ecotoxicological effects of microplastics in soils, there is a limited understanding of the reproductive toxicity of microplastics to soil organisms and the production of nanoplastics through biological fragmentation. We used the earthworm Eisenia andrei to investigate the generation of nanoplastics from polyethylene microplastics in soil ecosystems and to determine the negative effects of microplastic exposure on soil invertebrates. Earthworms were exposed to two different sizes of microplastic for 21 days, and various physiological features, including those pertaining to reproduction, were subsequently analyzed. Exposure to microplastics affected coelomocyte viability and caused damage to male reproductive organs, while having negligible effects on female reproductive organs. Earthworm-induced fragmentation of microplastics to nanoplastics was confirmed using scanning electron microscopy and energy dispersive X-ray analysis. These nanoplastics were introduced into soils through cast excretion. We provide the evidence of nanoplastic generation from ingested microplastics and damage caused to earthworm spermatogenesis through microplastic exposure.