The protective layer formed by soil particles on plastics decreases the toxicity of polystyrene microplastics to earthworms (Eisenia fetida)
Résumé
The recent discovery of microplastics contaminants in most ecosystems has raised major health issues, yet knowledge on their impact on soil organisms is limited, especially their toxicity evolution with aging. Here we studied the toxicity of polystyrene microplastics (PS-MP) to earthworm (Eisenia fetida) after microplastic aging in soil. Results showed that the 50% lethal concentration was 25.67 g/kg for microplastics, and 96.47 g/Kg for plastics that have aged 28 days in soil, indicating the toxicity of microplastics decreased with aging. Laser scanning confocal microscope and scanning electron microscope (SEM) reveal that the toxicity of microplastics to earthworm may be due to the ingestion of microplastics by earthworms and physical damage, e.g., epidermis abrasion and setae loss, induced by microplastics. Similarly, the levels of reactive oxygen species, antioxidant enzyme activities and malondialdehyde increased with microplastic concentrations from 0.1 to 1.5 g/kg, but decreased with aging from 7 to 28 days. The integrated biomarker response index also confirmed that the toxicity of microplastics decreased with aging. SEM show that microplastics were progressively covered by soil particles during soil aging, inducing the formation of protective layer and increasing the particle size of microplastics, which prevented direct contact with earthworms and decreased the ingestion of microplastics, and, in turns decreased microplastic toxicity. Overall, our study provides valuable insights for elucidating the effect of aging on the toxicity of microplastics.
Origine : Fichiers produits par l'(les) auteur(s)
