Microplastic ingestion induces changes in coelomocyte composition of Eisenia fetida

The earthworm Eisenia fetida is a widely used model organism for environmental toxicity assessment, including microplastic particles (MPP). Impacts of MPP at the organism level have been extensively documented, while effects on the cellular level and in particular the immune system of E. fetida are less well understood. Here we exposed earthworms outside soil for six days to food pellets containing no MPP (mock treatment), 10% (w/w) pure polystyrene (PS) MPP (25–75 μm), or 10% (w/w) PS MPP supplemented with 0.5% (w/w) of the antioxidant Irgafos 168 (PS Irgafos ). Immune cells (coelomocytes) were isolated from E. fetida using a non-invasive isolation method, and their number, viability, and subpopulation distribution (amoebocytes and eleocytes) were assessed by flow cytometry. The total number of isolated cells was not affected by MPP, while coelomocyte viability was significantly reduced after PS and PS Irgafos ingestion compared to mock-treated worms. PS Irgafos ingestion further decreased the number of living cells per mg fresh weight compared to PS ingestion. Ex vivo analysis of coelomocyte viability confirmed an enhanced toxicity of PS Irgafos compared to PS. Our findings show that MPP and their additives cause physiological changes and alter immune cell distribution compared to mock-treated worms, posing potential risks to soil invertebrates.