The application of parasiticides (e.g. ivermectin) to domestic animals can affect populations of dung-dwelling organisms and, in some cases, retard dung degradation. During the registration process, such parasiticides need to be tested at higher tier levels when adverse effects on dung organisms are observed in single species toxicity tests. Since no guidance on higher-tier testing was available, an international project was set up in order (1) to assess the robustness of field tests when conducted by four research groups at different geographic sites varying in dung and soil faunas and in environmental conditions, and (2) to study the effects of these variables on the interpretation of test results. The experiments were conducted in Lethbridge (Canada), Montpellier (France), Zurich (Switzerland), and Wageningen (The Netherlands). Ivermectin was used as test compound. The results indicate that ivermectin negatively affected various groups of dung flies and dung beetles at all study sites. However, ivermectin treatments did not seem to have an effect on the degradation rate of dung in temperate climate regions. Effects on soil fauna (on collembolans, but not on earthworms) living below dung pats only occurred rarely. The chosen study design proved to be suitable to evaluate the effects of parasiticides on dung insects and soil fauna under field conditions such as required in higher-tier testing for risk assessment.
The project results have been published as a series of papers in Environmental Toxicology & Chemistry. [read more]