| Pyrethroid is widely used around the world, and contributed greatly to the agricultural development. But a large portion of pyrethroid used in agriculture ends up as residuals in the soil, making soil-dwelling organisms more vulnerable to pesticide intoxication. Earthworm is one of the most common soil oragnisms in most environments, and plays an important role in the functioning of soil ecosystems. The analyzing of P450 enzyme activity in earthworm is a newly developed practice for soil pollution risk assessment. The toxicology of cypermethrin on the earthworm Eisenia fetida was evaluated by measurements of the acute response, growth, reproduction and CYP3A4 activity of the earthworm incubated on filter paper and in soil. The acute response test showed that 48 h-LC50 and 72 h-LC50 by the filter paper contacting method were 445.5 μg·cm-2 and 212.1 μg·cm-2, respectively, and 7 d-LC50 and 14 d-LC50 by the soil incubation method were 121.6 mg·kg-1 and 80.2 mg·kg-1, respectively. A low dose of cypermethrin induced the growth of the earthworm and the cocoon production in short time but restrained the incubation of juveniles. The CYP3A4 activity of the earthworm on filter paper was induced by cypermethrin at 21.5 ng·cm-2 and inhibited at 214.8 ng·cm-2. A 3-day exposure of cypermethrin at 10 mg·kg-1 significantly induced the CYP3A4 activity of the earthworm in the soil, and the inducting effect remained but tended to be weaker with the prolonging of the exposure time. The low toxicity of cypermethrin on the earthworm was revealed by the LC50, growth rate and cocoon production rate, with the sensitivity being in an order of enzymatic activity>growth and reproduction indicator>acute toxicity. However, the significant inverse U type dose-response relationship observed between the CYP3A4 activity and the concentration of cypermethrin reflected its endocrine disruption effect on the earthworm. This experiment also demonstrated CYP3A4 could be used as a potential biomarker to assess the ecological risk of pyrethroid pollution in soil. |
