Environmental tests on livestock drugs

Dung pat with a specific concentration of ivermectin. Credit: UZH

The authorization of veterinary medicinal products requires assessments for nontarget effects in the environment. Numerous field studies have assessed these effects on dung organisms. However, few studies have examined effects on soil-dwelling organisms, which might be exposed to veterinary medicinal product residues released during dung degradation.

Drugs for livestock can harm beneficial organisms that break down dung. Therefore newly developed medical substances need to be tested on single species in the lab. The problem is that sensitivity to toxic substances can vary significantly even among closely related species. This begs the question as to how representative tests on individual animal species are. Such tests on key species bear the risk that more sensitive species will continue to be harmed by a substance, thereby jeopardizing key ecosystem functions. 

An international research group now proposes to extend the current standard testing scheme and designed a panel consisting of a representative selection of all organisms that break down dung. The researchers tested the implementation of a more comprehensive higher-tier ecotoxicological field test based on the anti-parasitic drug ivermectin at four climatically different locations. Study sites were located in different ecoregions in Switzerland (Continental), The Netherlands (Atlantic), France (Mediterranean), and Canada (Northern Mixed Grassland) also representing different climates.

For the most part organisms were identified using classical morphology-based methods which worked reasonably well in well-studied environments but the authors had to resort to DNA barcoding in less known areas and they also pointed out that traditional methods won't cover the entire fauna that might be affected. Overall they were very pleased with the results:

Our field approach was therefore a success and in principle can be recommended. The regulation authorities responsible, such as the European Medicines Agency EMA, now have to decide whether this more conclusive yet more complex test should be required in the future. Classifying species via so-called DNA barcoding, based on each organism's unique genetic fingerprint, is possible in principle and will probably be more cost-effective in the future. However, this approach requires the establishment of a complete database for coprophilous organisms, which does not yet exist. 

We should be able to help with that.