Earthworms Modulate the Toxicity Effect of Low-Density Polyethylene on Plant Development

It is crucial to understand the effect of microplastics (MPs) on plant systems with the increasing accumulation of MPs in the soil ecosystem. Earthworm potential to accumulate and degrade microplastics could modulate the toxicity of microplastics to plant growth. In this study, a pot experiment containing 1000 g soil mixed with different concentrations of low-density polyethylene (LDPE) MPs with and without earthworms was performed for 45 days using the test plant Trigonella foenum-graecum. The results demonstrated that MPs affect plant growth and cause a reduction in terms of root length in all concentrations with respect to the control. In terms of shoot length, no significant differences were observed among the similar concentrations with and without earthworms. However, there is a significant difference in the number of root nodules among similar concentrations of LDPE with and without earthworms except between MP100 and E + MP100. The number of root nodules decreased as the dose of microplastics increased MP100 (8.33), MP500 (8.11), and MP1000 (7.33). The chlorophyll content including chlorophyll a (chl “a”), chlorophyll b (chl “b”), total chlorophyll, and carotene was decreased as the dose of LDPE increased, while the phenol and flavonoid content, as well as antioxidant activities such as ascorbate peroxidase (APOX), glutathione-S-transferase (GST), and guaiacol peroxidase (GPOX), were increased. The superoxide dismutase (SOD) and catalase (CAT) activities were reduced when compared to the control. The plant grown in the presence of earthworms showed better results in terms of overall plant development. Therefore, it is concluded that the earthworms modulated the stress induced by microplastics on plant development.