Understanding the harmful effects of polyethylene microplastics on Eisenia fetida: A toxicological evaluation

Microplastics, measuring less than 5 mm, are pervasive environmental pollutants raising concerns about their toxic effects on terrestrial ecosystems, especially earthworms.A comprehensive toxicological evaluation of polyethylene microplastics on earthworms will be beneficial for determining the detrimental impacts of these ubiquitous pollutants on soil ecosystem. Therefore, in the present study, the best representative soil organism, earthworms (Eisenia fetida), were opted for examining the toxicological effect of polyethylene microplastic. E. fetida were subjected to different concentrations of polyethylene microplastic (200, 400, 600, 800, and 1000 mg/kg) in soil and randomly picked out on days 7 to 56. Earthworms exposed to higher concentration of polyethylene (1000 mg/kg of artificial soil) showed a significant reduction in body weight and cocoon formation after 35th days of incubation. A consistent decrease in the concentration of carbohydrates, lipids, and protein was observed when the worms were exposed to the higher concentration of polyethylene. Further, antioxidant enzymes like superoxide dismutase, glutathione S-transferase, peroxidase, catalase, and malondialdehyde were determined for antioxidant stress.Exposure of 200 mg/kg to 1000 mg/kg of artificial soil caused a prominent amplification in the build-up of malonedialdehyde (a biological marker of oxidative stress) by 1.29-fold. It also considerably augmented the activity of the antioxidant enzymes viz., glutathione S-transferase (1.54-fold), superoxide dismutase (1.51-fold), peroxidase (1.25-fold), and catalase (1.87-fold). The present study's findings provide a new understanding of the toxic effect of microplastic on earthworm E. fetida, presenting a foundation for its risk evaluation on soil ecosystems and non-target biological toxicity.