Effects of polyethylene microplastics stress on soil physicochemical properties mediated by earthworm Eisenia fetida

Microplastics (MPs) are widely distributed in soil environments, but their ecological risks are not fully understood. To fill this knowledge gap, incubation experiments were conducted to explore the physiological response of Eisenia foetida (E. fetida) to polyethylene MP stress and its effects on soil physicochemical properties. E. fetida was incubated in soils amended with MPs of two particle sizes (13 μm and 130 μm) at six concentrations (0, 1, 3, 6, 10 and 20 g MPs·kg^-1 soil) under laboratory conditions. The toxicity of 13 μm MPs on the growth and survival of E. fetida was greater than that of 130 μm MPs. Excessive reactive oxygen species accumulation induced by high MP concentrations decreased superoxide dismutase activity and increased malondialdehyde content. Soil pH increased significantly in the 130 μm treatments. MPs increased the contents of soil organic carbon and available potassium. However, the presence of MPs did not significantly alter available phosphorus or nitrate nitrogen content. MP contamination in soil may have adverse impacts on the growth of earthworms, induce oxidative stress in earthworms, and change soil physicochemical properties. In addition, the effects of MPs are size-dependent and dose-dependent. This study provides new evidence for the ecological risks of MP pollution in the earthworm-soil systems.