The veterinary pharmaceutical ivermectin has been used for more than thirty years all over the world to combat parasites like roundworms, lice and mites in livestock and pets. The active ingredient belongs to the chemical group of avermectins, which generally disrupt cell transport. However, when ivermectin is used in high dosage excess quantities are excreted in the faeces of treated animals which also harms dung-degrading beneficial insects like dung beetles and dung flies. This has a profound impact on the the functioning of surrounding ecosystems. In extreme cases the dung is not decomposed and the pasture is destroyed.
Since 2000 public regulators in many countries therefore mandate standardized safety tests for the use of avermectin derivatives. A research team consisting of scientists from the University of Zurich and an ecotoxicology company in Germany, has now shown that the currently used safety tests are not able to sufficiently prevent environmental damage. Even closely related dung organisms react with varying degrees of sensitivity to the same veterinary pharmaceutical.
The group examined 23 species of sepsid flies that typically live in cow dung. It turns out that individual species vary by a factor of 500 in their sensitivity to ivermectin. Standardized safety tests typically performed in toxicology laboratories today are based on single, arbitrarily selected dung organisms. This poses the considerable risk that more sensitive species will continue to be harmed by ivermectin and that important ecosystem functions will suffer long-term damage as a consequence. In order to prevent this, safety tests should be extended to include a representative selection of all dung-degrading organisms, if not the entire community:
We close by reiterating that sepsid flies are very well suited as test organisms for any toxic residues in the dung of livestock or other large vertebrates, due to their ease and speed of rearing and handling. While the choice of a particular species will be crucial because species vary strongly in sensitivity, use of several local species can offset the arbitrariness of choice to some degree, rendering overall representative results. Sepsids as ecotoxicological test organisms could be particularly useful and economical in the tropics, where high-tech laboratory equipment is often not available.
By including more species in the tests costs for the authorization process would increase especially because all relevant organisms would need to be properly identified. For that reason the authors suggest to include DNA Barcoding in the test protocol as its inclusion would represent a rather modest increase in costs.