Effects of ivermectin application on the diversity and function of dung and soil fauna: Regulatory and scientific background information.

The application of veterinary medical products to livestock can impact soil organisms in manure-amended fields or adversely affect organisms that colonize dung pats of treated animals and potentially retard the degradation of dung on pastures. For this reason, the authorization process for veterinary medicinal products in the European Union includes a requirement for higher-tier tests when adverse effects on dung organisms are observed in single-species toxicity tests. However, no guidance documents for the performance of higher-tier tests are available. Hence, an international research project was undertaken to develop and validate a proposed test method under varying field conditions of climate, soil, and endemic coprophilous fauna at Lethbridge (Canada), Montpellier (France), Zurich (Switzerland), and Wageningen (The Netherlands). The specific objectives were to determine if fecal residues of an anthelmintic with known insecticidal activity (ivermectin) showed similar effects across sites on 1) insects breeding in dung of treated animals, 2) coprophilous organisms in the soil beneath the dung, and 3) rates of dung degradation. By evaluating the effects of parasiticides on communities of dung-breeding insects and soil fauna under field conditions, the test method meets the requirements of a higher-tier test as mandated by the European Union. The present study provides contextual information on authorization requirements for veterinary medicinal products and on the structure and function of dung and soil organism communities. It also provides a summary of the main findings. Subsequent studies on this issue provide detailed information on different aspects of this overall project. Environ Toxicol Chem 2016;35:1914-1923.