Objective  Ecotoxicity imposed by nonylphenol (NP) on Eisenia foetida and potential detoxification effect of tea polyphenols were studied.

  Method   Adding different concentrations of tea polyphenols into NP base solution, the relief of tea polyphenols (TP) on the life state, lethal toxicity, avoidance behavior and growth inhibition induced by NP were observed in E. foetida, and the toxic mechanism of NP was studied by HE staining.

  Result  At a concentration in soil ranging between 100-200 mg·kg⁻¹, NP exerted varied degrees of toxicity to the earthworms with lethality directly correlated with the concentration as well as exposure time. The growth of earthworms was retarded by 34% at 200 mg NP·kg⁻¹, and a high mortality rate observed when the concentration reached 400 mg NP·kg⁻¹. The stained tissues of the earthworms under NP stress showed decreased vacuolated gland cells, thinned circular muscles, bared cuticles, and thickened epidermis. Toward the soil with NP in the range of 12.5-200 mg·kg⁻¹, the earthworms displayed a movement avoidance. Upon the addition of tea polyphenols at the concentrations of 70-700 μg·kg⁻¹ in the NP solution, the lethality and growth retardation of the earthworms declined significantly. A tea polyphenols addition of 0.7-7 μg·kg⁻¹ in the NP solution significantly lessened the avoiding response of the earthworms. With 0.7-700 μg·kg⁻¹ of added tea polyphenols, the thickness of the muscular layer of the earthworm body wall increased and the stratum corneum became smooth again.

  Conclusion   NP at a concentration in the range from 100 mg·kg⁻¹ to 400 mg·kg⁻¹ in soil could be toxic or lethal to E. foetida. Whereas, the presence of tea polyphenols at a level between 0.7 μg·kg⁻¹ and 700 μg·kg⁻¹ in the NP solution that was blended in the soil could significantly mitigate the adverse effect induced by NP.