Pet parasiticides polluting rivers, researchers find
Parasite treatments for pets often contain chemicals banned in agriculture.
Parasiticide products used on small animals are causing harmful pollution in UK rivers and ponds, according to a new briefing paper from the Grantham Institute at Imperial College London.
The researchers found that chemicals from parasiticides are entering waterways in concentrations that are known to be harmful to aquatic species. Urban areas are particularly affected.
Pet parasiticides often contain either imidacloprid or fipronil, chemicals which are effective at killing invertebrates such as fleas, ticks, and mites. However, when they enter natural freshwater environments through household wastewater and sewer overflows, they are harmful to aquatic invertebrates such as mayfly and dragonfly larvae, in turn causing problems in the wider ecosystem as fish, birds, and bats feed on them.
Imidacloprid, alongside other neonicotinoid chemicals, has been banned for agricultural use on crops since 2018, owing to its impact on bees and other pollinators. However, its use on small animals is still permitted and it is found in 138 pet parasiticide products authorised in the UK.
The paper calls for increased regulation of veterinary parasiticides and more monitoring and stewardship to minimise the impact of parasiticide pollution on aquatic ecosystems.
Dr Andrew Prentis, visiting Fellow in the Grantham Institute and a member of Vet Sustain, said: “So far, our use of parasiticides for pets has focused primarily on the animal and human health benefits, but even these are not well evidenced. Chemicals that have been banned in one sector are used indiscriminately in another with seemingly little consideration of the possible risks.
“This not only results in increased pollution of UK waterways – which are under myriad threats from other sources of pollution – but could also lead to parasite resistance due to overuse. It’s time for a reassessment of clinical need and treatment recommendations.”
In response to the paper, the BVA is calling for more research into the problem and is encouraging its members to avoid blanket treatment.
BVA senior vice-president Justine Shotton said: “Parasiticide treatments do an important job in preventing, treating and protecting both animals and humans from illnesses and conditions linked to parasites. However, it is important to consider the impact these products may have on the environment. There are still many knowledge gaps surrounding parasiticide products, so this research – although shocking – by the Imperial College is welcome.
“The British Veterinary Association is working to raise awareness of the issue within the veterinary sector and is developing resources to support vets in making risk-based decisions about when to treat. This is a true One-Health problem, with veterinary professionals needing to balance animal health, human health, and the health of the wider ecosystem. Pet owners should always speak to their vets, who will talk through different parasiticide options to find the best solution to prevent and treat parasites as needed for their pet.”
BSAVA is to partner with BVA Live (11-12 June 2026) to champion clinical research.
