Domestic canine faecal waste is a source of environmental pollution. Dog owners are increasingly adopting more environmentally friendly methods of dog faecal waste disposal including vermicomposting using earthworms. Many owners give their dogs medication to control parasites. While veterinary drugs target organisms that infect a host animal, they can also have an effect on non-target species in the environment. However, there is currently no research on the impact of canine anti-parasitic drugs on soil invertebrates or their effect on compost earthworms.
The most common anti-parasitic drugs for dogs are broad spectrum, treating external flea and tick infestations, intestinal nematode infections and heartworm. Many of these drugs contain two active ingredients: milbemycin oxime and afoxolaner. Milbemycin oxime is a macrocyclic lactone used in dogs and cats, with little known about its ecotoxicity to non-target species in soil or compost. Similarly, afoxolaner is one of a new class of drugs called isoxazolines and there are no studies on the toxicity levels of these pharmaceuticals on non-target soil-based organisms or compost.
This study evaluated how dog faeces treated with a broad spectrum anti-parasitic containing milbemycin oxime and afoxolaner affects the survival, growth, and reproduction of Eisenia fetida in a simulated compost environment. Laboratory based experiments were conducted over two months following modified OECD guidelines for earthworms: Acute Toxicity (Test 207) and Reproduction (Test 222). Test worms were fed treated dog faeces at one day and six-day intervals to measure the toxicity of drug residues during the treatment cycle. Significance of results and their implication on the suitability for vermicomposting treated domestic canine faecal waste will be discussed.