Ecotoxicological effects of microplastics and cadmium on the earthworm Eisenia foetida

As microplastics (MPs) have become ubiquitous in both aquatic and terrestrial environments, there has been a growing concern about these new anthropogenic stressors. However, comparatively little is known about the negative effects of MPs, co-contamination of MPs and heavy metals on terrestrial organisms. The objective of this study was performed to understand the adverse effects of exposure to MPs and co-exposure to MPs and cadmium (Cd) on the earthworm Eisenia foetida (E. foetida). Results showed that exposure to MPs only or to a combination of MPs + Cd decreased growth rate and increased the mortality (>300 mg kg^-1) after exposure for 42 d, with MPs + Cd (>3000 mg kg^-1) posing higher negative influence on the growth of E. foetida. Exposure to MPs might induce oxidative damage in E. foetida, and the presence of Cd accelerates the adverse effects of MPs. Furthermore, the MPs particles can be retained within E. foetida, with values of 4.3-67.2 particles·g^-1 earthworm, and can increase the accumulation of Cd in earthworm from 9.7%-161.3%. Collectively, the results of this study demonstrate that combined exposure to MPs and Cd poses higher negative effects on E. foetida, and that MPs have the potential to increase the bioaccessibility of heavy metal ions in the soil environment.