Published 5th Jul 2026, 06:00 BST
Environmental chemist Professor Alistair Boxall told the House of Lords Environment and Climate Change Committee inquiry into treatments leaving ‘forever chemicals’, such as highly soluble organofluorine compound trifluoroacetic acid, were being seen in very high concentrations in rivers, and concentrations appeared to be rising.
The inquiry follows the Veterinary Medicines Directorate (VMD) proposing changing the status of certain pet parasite treatments from a general licence to restrict their sale to largely through vets and pharmacists.
The inquiry focused on pesticides such as permethrin, which is used in humans for head lice treatment and for agricultural uses, as well as fipronil and imidacloprid, following concerns raised by the VMD and the Environment Agency.
It heard a major concern included that many of the chemicals such as imidacloprid are highly water soluble and as it entered water it brought a range of biodiversity into contact with it, such as mayflies, dragonflies and caddisflies, a common prey source of species such as salmon and trout.
The inquiry was told the affected invertebrates are critically important in the food web, linking the basal processes that allow energy to move through the food web through to these higher trophic levels, such as fish and other species, including birds.
Prof Boxall said a large-scale project in which Yorkshire’s rivers have been continuously monitored for a year found the molecule fluralaner in only a couple of the hundreds of samples taken, but that did not mean that fluralaner does not pose an environmental risk. He said: “It could well be that it is sticking to the sludge, and that sludge is then going on to the land and carrying the fluralaner with it. That really needs to be looked at.
“For other molecules we have looked at, we have had occasional detections of moxidectin and pyriprole. We have also looked at permethrin, which we detected quite a lot across Yorkshire.”
Prof Boxall told the peers some of the main pathways to the drugs getting into Yorkshire’s watercourses included chemicals going down into the sewer system due to the washing of skin after application, the washing of bedding and surface run-off.
He said: “I never thought I would say this to a Lords committee but, when the dog’s poo is on the pavement, it can get washed off. Then you have the poo bags, which are going to be disposed of somewhere, so there will be a route into landfill. We are recognising that dogs swimming is going to introduce these molecules.
“One of the processes by which chemicals are removed in wastewater treatment is that they stick to sewage sludge. If you look at the ingredients in some of these products, some of them have properties that would mean they stick to sewage sludge quite extensively.”
Prof Boxall said while European guidelines on the drugs required an environmental assessment, some have been developed for livestock medicines and aquaculture medicines and testing was patchy. He said: “Effectively what a market authorisation applier will do is work through a set of questions and, if they meet some of those questions, they stop. That is one of the issues with the pet medicines.
“When the guidelines were developed, it was assumed that environmental emissions would be low and therefore impacts would be low, but in the UK we have 22 million cats and dogs and we have prophylactic use of these molecules. We are in a situation where usage is no longer low, and it is not really appropriate to stop at that phase.”
Prof Boxall recommended to the committee action to promote the development of safer alternatives and innovating by looking at things that are less toxic and harmful to the environment. He said a proper environmental risk assessment was needed for all flea treatments and wormers as part of the authorisation process.
Prof Boxall said when the environmental risks of ingredients in the pet treatments outweighed their benefits, they should not be authorised.
While manufacturers of the treatments say responsible pet ownership means proactively planning to prevent and control parasites regularly, Prof Boxall said industry advertising had spread unnecessary fears. He added: “We should stop the prophylactic use of these molecules, and we should ban the advertising that happens at the moment. Almost daily, I get in my social media feed an advert trying to sell me a flea treatment. They are scaremongering.”
