Individual and combined effects of herbicide tribenuron-methyl and fungicide tebuconazole on soil earthworm Eisenia fetida

Earthworms are soil engineers that alter the soil bio-physical properties to favor plant growth whereas pesticides represent a significant threat to their abundance and soil health. Thus, we investigated the toxic effects of tribenuron-methyl (TBM) and tebuconazole (TEB) on the soil earthworm, Eisenia fetida. The TBM demonstrated low toxicity to E. fetida in the contact filter paper and artificial soil tests, with median lethal concentrations (LC₅₀) of 135.6 μg cm^-2 at 48 h and 511 mg kg^-1 on day 14, respectively. Similarly, TEB also showed low toxicity to E. fetida in the artificial soil test with LC₅₀ of 287 mg kg^-1 on day 14. However, TEB was highly toxic to earthworm in the contact filter paper test with LC₅₀ of 5.7 μg cm^-2 at 48 h. The mixture of two pesticides had an antagonistic effect on the earthworm. Under 0.1 LC₅₀ of TBM and TEB, either single or combined application of pesticides induced oxidative stress and inhibited cellulase activity in early days of the earthworm exposure. However, both pesticides did not damage the earthworm DNA. Our results suggest that pesticides can negatively affect soil earthworms and provide valuable information regarding the responses of soil biological engineers to the lethal agrochemicals.