Effects of triclopyr on the earthworm (Eisenia fetida) under laboratory conditions: assessment of growth inhibition and oxidative stress

Abstract

Triclopyr is a widely used systemic herbicide in forestry and agricultural management. However, its potential sublethal effects on non-target soil organisms remain insufficiently understood. In this study, the chronic toxicity of triclopyr to the earthworm Eisenia fetida was systematically evaluated under laboratory conditions, with a focus on growth inhibition and oxidative stress responses. Earthworms were exposed to triclopyr-amended artificial soil at concentrations of 0–10 mg kg⁻¹ for 28 days. Growth performance was assessed using growth inhibition rate (GIR) and specific growth rate (SGR), while oxidative stress was evaluated through a suite of biomarkers, including reactive oxygen species (ROS), malondialdehyde (MDA), superoxide dismutase (SOD), catalase (CAT), guaiacol peroxidase (POD), and glutathione S-transferase (GST). An integrated biomarker response index (IBRv2) was further applied to quantify cumulative physiological stress. Results showed that triclopyr exposure induced significant, time- and concentration-dependent effects. Growth inhibition was evident during early and mid-exposure periods, while delayed negative SGR values indicated cumulative growth impairment under prolonged exposure. ROS and MDA levels increased markedly, with MDA reaching up to approximately fourfold higher than the control at 10 mg kg⁻¹ after 7 days, demonstrating pronounced lipid peroxidation. Antioxidant and detoxification enzymes exhibited an initial induction followed by partial suppression during chronic exposure, suggesting a transition from compensatory defense to oxidative dysfunction. IBRv2 values peaked at day 7 and increased again at day 28, with maximum values observed in the highest concentration group, indicating substantial integrated biological stress. This study provides a comprehensive assessment of triclopyr-induced growth inhibition and oxidative stress in E. fetida using a multi-biomarker and IBR-based approach, offering valuable insights for ecological risk assessment of triclopyr in terrestrial environments.