Responses of earthworm growth and oxidative stress to microplastic addition

With the wide application of agricultural plastic mulch film in China's farmland, the accumulation of microplastics in farmland soil environment is increasing. The toxic effects of different types and quantities of microplastic residues on soil organisms are still unknown. To explore the issues, an indoor culture experiment was carried out. In this study, earthworms were exposed to three different plastic films (polyethylene (PE), polyethylene terephthalate-butylene adipate (PBAT), polybutylene terephthalate-adipate + polylactic acid (PBAT+PLA)) with four concentration gradients (0, 0.5%, 1%, 2%) in the soil. The changes of earthworm biomass, antioxidant enzyme activities including glutathione, glutathione-S-transferase, peroxidase, superoxide dismutase, catalase, malondialdehyde (MDA) and reactive oxygen species were examined to evaluate the biological toxicity of microplastics. With the increase in microplastic concentration, the earthworm biomass shows a trend of initial increase and then decline. In the convalescent period, the MDA of PBAT at 2% concentration is significantly increased by 34.9% compared with CK, showing more severe oxidative damage. The addition of microplastics significantly increases all antioxidant enzyme activities simultaneously. The addition of three types of microplastics increases the toxicity risk of earthworms, while the biological injury caused by PBAT is more severe than PE. This study provides theoretical basis in evaluating the ecological risks from different types of microplastic and their residual concentrations.