Effects of polystyrene microplastics on accumulation of pyrene by earthworms

Micro- and nano-plastics (MNPs) are recognized as a class of emerging and ubiquitous contaminants in soil, which influence the behavior of pollutants and have potential adverse impacts on organisms. This study explored the potential mechanisms of polystyrene microplastics (MPs, 10 μm) and nanoplastics (NPs, 100 nm) with different concentrations (10 and 100 mg/kg) in soil on the accumulation and elimination of pyrene in earthworms, Eisenia fetida. MPs facilitated the accumulation of pyrene by earthworms in the first week via injuring the integrity of earthworm intestine. The representative antioxidant enzyme activities indicated that MPs induced severer oxidative stress to earthworms than NPs, especially at the concentration of 100 mg/kg, thus leading to increased accumulation of pyrene by earthworms at the initial stage. In addition, high-throughput 16S rRNA gene sequencing demonstrated that NPs inhibited the pyrene-degrading bacteria in earthworms, resulting in the higher concentration of pyrene in the end. The results elucidated the effects of MNPs with different sizes and concentrations on the accumulation of organic pollutants in the terrestrial invertebrates.