Species-specific biomarker responses reveal differential toxicity of microplastic type and concentration in Folsomia candida and Sinella curviseta.

Microplastics are recognised as terrestrial pollutants, but their sublethal effects on soil fauna remain poorly understood. We examined biochemical responses to three environmentally relevant microplastic types in two Collembola species, Folsomia candida and Sinella curviseta. Juveniles were exposed for 28 days in standardised soil to 0-10,000 mg kg-1 of polystyrene-HBCD, car tyre abrasion or a starch-based bioplastic blend. Analysed biomarker responses included acetylcholinesterase, carboxylesterase, catalase, and glutathione S-transferase activities; glutathione, reactive oxygen species and carbohydrate concentrations. Multivariate analysis showed that Species explained 84% of biomarker variation, whereas Type and Concentration had weak but significant effects. Car tyre particles induced the strongest glutathione S-transferase, glutathione, and reactive oxygen species responses in both species. Polystyrene-HBCD stimulated detoxification responses, while the starch blend caused weaker changes. Concentration effects were significant but non-linear and species-specific. These findings demonstrate species- and polymer-specific responses and support multivariate biomarkers as indicators of stress in soil invertebrates.