Reproduction, metabolic enzyme activity, and metabolomics in earthworms Eisenia fetida exposed to different polymer microplastics

Plastics degradation generates microplastics (MPs), posing a risk to soil function and organisms. Currently, the impact of MPs derived from different polymers remains poorly understood. In this study, the effects of three polymers (polypropylene (PP), polylactic acid (PLA), and polybutylene adipate terephthalate (PBAT)) were investigated at environmentally relevant levels (0, 0. 5, 2.5, and 10 g/kg) on the growth, reproduction, metabolic enzyme activities (CYP1A2, CYP2B6, CYP2C9, CYP3A4, SOD, and CAT), and metabolomics of earthworm Eisenia fetida during a 28-day exposure period. The presence of smaller plastic particles inside earthworms (<62 µm), and polymer-specific and concentration-dependent effects on earthworms were observed. Compared with the controls, both PBAT (2.5-10 g/kg) and PLA (10 g/kg) significantly inhibited earthworm reproductive output, measured as the sum of cocoons and young earthworms, caused significant alterations in the majority of the top fifteen most important metabolites (such as arachidic acid, fumaric acid, L-malic acid, myo-inositol, cytosine, and deoxyinosine), and inhibited the activities most tested enzymes. The highest PP concentration (10 g/kg) only significantly changed the levels of (9Z,11E,15Z)-(13S)-hydroperoxyoctadeca-9,11,15-trienoate (13-HPOT), L-formylkynurenine, and kynurenine. Enzyme activity and metabolomics alterations indicated that all three types of MPs induced oxidative damage, neurotoxicity, immune-metabolic disorders, and disrupted lipid and tryptophan metabolism in earthworms, while PBAT and PLA also induced dysregulation of energy metabolism, purine and pyrimidine metabolism, and osmotic pressure regulation homeostasis. PBAT MPs exhibited the strongest toxicity, with adverse effects observed at the lowest tested concentration.