Flea treatments are turning our pets into an environmental hazard – there has to be a better way

The Guardian

23-02-2025

When I was 10, I succeeded in my campaign for a family dog. Part of her care, and our joy as owners, was the monthly application of spot-on worm and flea treatment. With veterinary medicine on my mind as a career, I relished the theatre of vets-at-home. We bought doses over the counter, scheduling the dog's treatment on the calendar like a five-a-side.
We applied these drugs to our dog because every other owner did. Because it was encouraged, because it was easy, because it felt right.
New research confirms the use of such veterinary drugs as an unmanned checkpoint in the landscape of environmental contamination. Put simply, caring for our dog was polluting the natural world. A study from the University of Sussex reveals songbirds as the latest victims. Blue tits and great tits are two of many birds that line their nests with animal fur. Every sampled nest contained fipronil and 89% contained imidacloprid and permethrin – three insecticides so potent they have been banned for agricultural use in the UK and EU, but can be bought by anyone for use on pets.
In the study, nest mortality correlated with drug concentration. Eggs never hatched; chicks expired after hatching – at a time when almost half of all UK bird species are in a state of serious decline. 'The simplest explanation is that eggs and chicks are getting a sufficient dose of pesticide from the nest lining to kill. There's enough medication in the environment to pollute every single blue and great tit nest,' says Prof Dave Goulson, a co-author of the study.
Bird nest pollution mirrors the state of our rivers. Studies by Dr Rosemary Perkins found fipronil persists in 99% of samples taken from 20 English rivers, with imidacloprid found in 66% of samples. My dog was one of the approximately 17.5 million cats and dogs in the UK – about 80% of the total of 22 million – that get regular over-the-counter worm and flea treatment, whether suffering from an infestation or not. One flea treatment of a medium-sized dog contains enough pesticide to kill 60 million bees. Will it take the silence of vanishing biodiversity for us to hear nature's cry?
Goulson is one of many scientists warning of collateral damage from veterinary drugs, but a regulatory blind spot has kept the environmental repercussions largely hidden – hushed like an interruption. Pet medications aren't subject to the same risk assessments as they are for use on livestock. When flea treatments entered the market in the 1990s, their environmental impact was assumed trivial.
I sense the veterinary profession has been caught off-guard by this ethical battle of balancing pet health with environmental responsibility. 'It's a real dilemma,' says Dr Sean McCormack, a small animal vet and conservationist. 'As a vet, you've taken an oath to 'protect and enhance animal welfare'. But you're contaminating nature – how did we miss this?'
Pets aren't the only source. A recent study shows that handwashing by owners in the weeks after spot-on treatment is also a major contributor. And McCormack describes the down-the-drain pathway of fipronil administered in 'insane quantities' across equestrian facilities to protect hooves and fetlocks against feather mites. Horses return to muddy fields, and fipronil leaches into water and soil, fast and unseen. Vets find themselves in a tough position. They are constrained by the absence of viable alternatives, the expectations of millions of pet owners trying to do the right thing, and the biological phenomenon of the flea.
Flea infestations can be fatal, and effective flea treatments must eliminate more than 90% of fleas in the environment. Otherwise, their staggering reproductive rate – a flea can lay 50 eggs a day – makes control nigh impossible. Fleas spend most of their life cycle away from their host, making eradication even more challenging.
As for alternatives, flea collars and oral tablets generally contain many of the same harmful chemicals as spot-on treatments. Alternative chemical treatments are either potent toxins or essential oils with no proven efficacy.
There is a serious economic argument to lessen animal medication overall. 'We could probably remove 80-90% of any of these chemicals with immediate effect,' says Goulson, who also rightly challenges our bewildering, increasing obsession with pets.
Reducing pet medication could structure a case-by-case approach. 'Most practices are improving – tailoring application schedules to suit the individual pet and owner's lifestyle,' says McCormack. If the dog is allergic to fleas, they should be prescribed monthly treatment. But treatment shouldn't be preventive. You wouldn't treat an empty scalp for head lice, and the same goes for fleas: if there is no infestation, keep a lid on it.
We should also welcome recommendations to bond with our pets through husbandry, attentiveness on walks and home hygiene. Regular grooming can detect parasites early, allowing for reactive treatment. Washing pet bedding in hot water every few weeks and vacuuming sleeping areas help eliminate flea eggs and larvae that live there.
And if your pet does require treatment? 'Please don't let them enter watercourses at all,' McCormack implores, citing further work from Goulson's lab that observed lethal doses of medication washing off dogs 28 days after application. How does that measure up to brand advice on the back of the packet? Most recommend a mere '48 to 72 hours' of water abstinence after treatment. Pharmaceutical companies place poison in the palm of our hands.
Veterinary surgeon Claire Whittle works with farmers to treat livestock strategically, and argues that spring is the perfect time to broach the conversation about using less medication with your vet. And countryside management like rotational grazing and taller grasses can be as effective at reducing parasite exposure as some pesticides. Native species such as sainfoin and chicory not only pose a structural challenge for parasites, but they contain natural insecticides. 'Diversifying plants could be better for animal health as well as wildlife health. Medication should not be the first line of defence,' says Whittle.
Looking ahead, parasites are evolving with worsening climate breakdown, spreading new disease risks. But on the brighter side, some countries are improving regulation. Ireland is making flea and worm treatments prescription only, offering a valuable case study for future policy changes in the UK. Could this spur urgent cooperation between industry regulators, the Veterinary Medicines Directorate, pharmaceutical companies and the pet-owning public?
Protecting our pets should never come at the cost of protecting nature. And I worry this uniquely human business of eliminating parasites, mixed with private sector procrastination to find and fund regulated, alternative veterinary medication, risks us morphing into the most hedonistic parasite of all. But parasites have little to gain from killing their host. They must keep them alive, in symbiosis. There is power for change, in our poisonous hands.
Sophie Pavelle is a writer and science communicator