Impacto da ivermectina sobre Eisenia foetida e atividade microbiana na vermicompostagem de esterco bovino

Abstract

The potential sources of pollutants originating from agroindustry operations include animal wastes, veterinary drugs, pesticides and other chemicals such as detergents and disinfectants. The avermectins are extensively used in veterinary medicine and agriculture. Most of these agents are excreted to some extent 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 objective of this study was to evaluate the influence of ivermectin on Eisenia foetida earthworms, by analyzing survival, growth, cocoon production, enzyme activities and behaviour during the vermicomposting of cattle manure under laboratory conditions. Furthermore, the chemical changes and microbial activity of the vermicompost were also studied. The earthworms (n = 10, with three replicates) were exposed to the test substrates contaminated with ivermectin 0, 1, 5, 10, 50 and 100 mg kg-1. Significant differences were tested using analysis of variance (ANOVA) followed by Duncan's test. Furthermore, regression models were applied to check a dose-response effect. In this study, there was no negative effects of ivermectin on mortality of earthworms. Likewise the chemical characteristics and microbial activity of vermicompost were not affected. The results show that avoidance test behaviour was not adequate to determine the toxicity of ivermectin for Eisenia foetida in cattle manure. However, a hormetic response was recorded on the growth and relative enzyme activity of acetylcholinesterase, catalase and alkaline phosphatase in earthworms. In addition, the results showed decreased values of the glutathione- s-transferase enzyme activity and increased levels of hydroperoxides levels in response to the higher concentrations of ivermectin at 7 days of treatment. On the other hand, after 28 days glutathione- s-transferase activity was significantly increased (p < 0.01) in the exposure to 50mg kg-1 and 100mg kg-1. In conclusion, acute exposure of ivermectin at high concentrations cause cellular injury in earthworms. Additionally, the presence of hormesis induced by ivermectin in Eisenia foetida may be related to activation of adaptive pathways.