Most of the veterinary pharmaceuticals are excreted in the faeces of treated animals and it has been demonstrated that members of the avermectin group may have deleterious effects on non-target organisms utilising the faeces. The aim of this study is to determine the sublethal effects of ivermectin on the Eisenia foetida earthworms. Earthworms were exposed to ivermectin at 0, 1, 5, 10, 50 and 100 mg kg-1 concentrations; samples were taken at 7, 14, and 28 days exposure for determination of survival, growth rate, cocoon production and enzyme activities. Furthermore, the chemical changes and microbial activity of the vermicompost were also studied. There was no negative effects of ivermectin on mortality of earthworms. Likewise the chemical characteristics and microbial activity of vermicompost were not affected. However, the results showed that ivermectin at low concentrations induces an increase in the activity of alkaline phosphatase and growth of E. foetida, but high concentrations inhibited these endpoints, and this was reflected in an inverted U-shaped curve, a graphic representation of hormetic effect.
earthworms; hormetic effect; toxicity; veterinary pharmaceuticals
