May 2026
The principle that we must prevent ecologically destructive levels of persistent nerve agents building up in the environment must have almost universal endorsement. But the principle that people should protect their pets from discomfort and even the low risk of disease is also one everyone can sign up to. When products we use to protect our pets cause massive environmental destruction something has to change. This is not a question of balancing objectives; this is about finding solutions that deliver for both objectives.
A profound failure of ecological vigilance by environmental regulator and Defra agency the Veterinary Medicines Directorate (VMD) has resulted in 20 years of covert environmental damage from Fipronil and Imidacloprid flea treatments; until I discovered the pollution in 2017.
The VMD is responsible for authorising environmentally safe veterinary medicines, and for pharmacovigilance – making sure that data is gathered to prove that when used the medicines do not harm pets, people or the environment.
However, there is no monitoring or environmental risk assessment for most of the 22 authorised flea treatment chemicals. Everyone is currently blind to the environmental risk they pose. As I write a wide range of veterinary medicines could be causing profound environmental damage, no one is looking.
By contrast, the authorisation of pesticides generally involves environmental risk assessments and publicly available information. Restricting, and particularly banning, environmentally damaging pesticides and other biocides creates a market pressure to innovate and develop more environmentally safe chemicals. That simply does not currently happen with veterinary medicines.
When you pick a bottle of bleach off a supermarket shelf it is branded with a big red diamond, framing a dead tree and a dead fish, and a bold statement “Very Toxic to Aquatic Life”. But Fipronil, for example, is much more toxic than bleach, it is poisonous to invertebrates in the same way that minuscule traces of novichok are poisonous to humans; a smear of Fipronil the size of a sand grain is enough to cause environmental damage in a Olympic swimming pool size lake. Yet when you pick a Fipronil flea treatment box off the same shelves there is no visible environmental warning on the box. Only when you get home and open it are you faced with 220 square centimetres of 2 mm high text. Which, if you can find it, says in one place “Fipronil may harm fish and other water creatures. Do not contaminate ponds, waterways or ditches with the product or empty containers. Do not allow dogs to swim in ponds or other waterways for 2 days after treatment.”
In fact, we know these chemicals are causing harm to water creatures and that allowing a dog to swim up to 28 days after treatment will cause a pollution incident. It is hardly surprising that 86% of dog owners are completely unaware that just using these flea treatments causes environmental damage.
Nearly a decade after I discovered this environmental calamity no significant action has been taken to reduce to the pollution levels.
My new independent review of the crisis demonstrates that the damaging levels of environmental pollution are directly attributable to flea treatment use. It summarises the avalanche of new scientific evidence of environmental damage, some of which confirms predictions from laboratory studies, and which also includes tragic new examples of environmental damage.
Natural England are concerned that flea treatments may have caused a 90% decline in damselfly numbers on a nature reserve in the Broads National Park – which we would expect because Fipronil and Imidacloprid in Japan have caused a 99% decline in dragonfly numbers. Numbers of mayflies, caddisflies and stoneflies are depressed downstream of sewage works all over the UK – which we would expect because in Germany Fipronil reduces populations of these insects in forest streams where maximum pollution levels are below the average level in a UK river sample. Populations of Blue Tits and Great Tits are in decline, particularly in England, which, again, we would expect because the higher the concentration of flea treatment in fur-lined birds’ nests, the more dead baby birds you find.
Some of the new science is surprising and alarming:
The VMD has recently opened a call for evidence on their proposal to remove Fipronil and Imidacloprid from the shelves and put them behind counters and online. Supposedly this will result in more advice to users, although how much advice happens when someone clicks a button to approve your online sale? In any case pollution occurs when you follow VMD advice and wash your hands after application or allow a dog to swim a week after treatment. An abundance of advice would make no significant difference to pollution levels. The VMD have indicated they are intending to spend 12 months or more taking and applying this decision.
Such trifling and slow measures enable environmental destruction.
My review shows that we now need a 98% reduction in Fipronil pollution and an 84% reduction in Imidacloprid pollution to get them down to levels where environmental harm is only occasional.
In my review I assess a wide range of actions that could be taken, tackling pollution at source, tightening up the pathways into the environment, and ensuring trade waste and sewage containing high levels of these nerve agents cannot simply be discharged into rivers.
Fixing sewage works so they can remove the chemicals will take decades, and this crisis needs addressing now.
Keeping Fipronil and Imidacloprid on the market damages the environment but does not help pets; there are 20 effective alternative flea treatments available. The only beneficiaries of this regulatory failure are the makers and sellers of Fipronil and Imidacloprid.
Over 95% of current use of these two chemicals in the UK is flea treatment use, while addressing the small residue pollutions from other sources may help, stopping at source has to mean dramatically and urgently reducing their use as flea treatments. This is the only timely and effective solution.
There is already a process set out in the legislation to deal with this situation.
The Veterinary Medicines Regulations 2013 states “The Secretary of State must update the assessment report whenever new information that is of importance and relates to the quality, safety or efficacy of the veterinary medicinal product becomes available”.
Having updated the assessment report the Secretary of State must decide if the product is safe to use, if not, or if there is insufficient information to be sure, then, in either case, the product should be suspended.
In addition, under the Habitats Regulations 2017 the VMD must also be certain that authorising the use of the products will not harm protected sites or species.
Despite the evidence of ecosystem damage, the VMD is apparently yet to initiate these statutory processes for addressing environmental harm from an approved veterinary medicine.
Fipronil is a PFAS forever chemical and Imidacloprid is a neonicotinoid. Both have been banned in agriculture because of the wildlife destruction they caused. How many more years of environmental destruction will be enabled before they are banned as flea treatments and, perhaps more importantly, will equally environmentally damaging chemicals step into their shoes? If the flea treatments of the future have not previously been used as agricultural pesticides, then we may have almost no data to assess the risk they present to wildlife.
My review contains recommendations aimed at improving market regulation to ensure there is no repeat. In essence we need vastly improved environmental risk assessments for all highly toxic veterinary medicines and we need to then monitor the approved chemicals in the environment to make sure that concentrations stay within safe limits.
Showing the veterinary medicine industry that damaging chemicals will not be allowed, will catalyse much needed innovation and drive the market towards less environmentally risky solutions.
And there is hope, not only are there alternative, even non-chemical, methods for dealing with fleas and ticks, there are also essential plant oils that appear to be effective, but have not been submitted for authorisation as medicines. Furthermore, some approved flea chemicals are less persistent, are more narrowly toxic and/or are ingested by pets rather than being poured onto their fur; so may be less environmentally damaging. We must have faith that applying a pressure in the veterinary medicines market for environmental safety will create space for less harmful products.
The opinions expressed in this blog are the authors' and not necessarily those of the wider Link membership.
Latest Blog Posts