A new study released today (Thursday 1 February, 2024) by researchers at the University of Sussex and Imperial College London has found that pet owners using flea treatment on their pets, risk contaminating their hands with toxic pesticides for at least 28 days after the treatment has been applied. Highly toxic pesticides used in the flea products are then flowing down household drains when pet owners wash their hands. Wastewater from sewage treatment works is a major source of fipronil and imidacloprid pollution in rivers – with concentrations in rivers exceeding safe limits for wildlife.

Fipronil and imidacloprid are highly toxic pesticides that are no longer approved for use in outdoor agriculture; imidacloprid belongs to the notorious group of pesticides known as neonicotinoids. However, these chemicals continue to be widely used in pet flea treatments, typically applied to the back of the pet’s neck (known as spot-ons) once per month.

Professor Dave Goulson from the University of Sussex, who supervised the research, explains: 

“These two chemicals are extremely potent neurotoxic insecticides and it is deeply concerning that they are routinely found on the hands of dog owners through ongoing contact with their pet. Pet owners will also be upset to learn that they are accidentally polluting our rivers by using these products.” 

The researchers collected samples from 98 dogs treated with spot-on fipronil or imidacloprid and evaluated the contribution of owner handwashing, dog bathing and washing of dog bedding to household sewage and subsequent wastewater pollution. The research found that wash off of pesticides occurred across all three pathways.

But owner handwashing was found to be the largest source of emissions with fipronil or imidacloprid detected in all tests on pet owners for at least 28 days after a spot-on application to their pet. Current guidelines advise that owners should not touch pets until the application site is dry, but this research shows that pollution is occurring continuously for the entire duration of action of the product.

This study builds on previous research conducted by the Sussex experts, which found that fipronil was detected in 98% of freshwater samples, and imidacloprid in 66%.  

The researchers are now calling for a review of regulatory and prescribing practices, as current pet flea products do not consider the extent of river pollution from down-the-drain wash off prior to regulatory approval. The research has demonstrated that even when product instructions are followed, substantial emissions to the aquatic environment are still generated.

The British Veterinary Association has recently issued a policy statement recommending that veterinary businesses should avoid blanket year-round parasite treatment policies and instead empower individual vets to have informed discussions with their clients (BVA, 2021). 

Professor Guy Woodward, Imperial College London says:

“Despite these chemicals being banned from outdoor agricultural use for several years, we are still finding them in UK freshwaters at levels that could harm aquatic life.  This paper shows how domestic pet flea and tick treatments, a largely overlooked but potentially significant source of contamination, could be polluting our waterways.”

Martin Whitehead, Clinical Director of Chipping North Vets also tells us:

"This study shows conclusively that dog spot-on flea and tick treatments are a major contributor to the demonstrated fipronil and imidacloprid pollution of the UK's rivers.  Indeed, when other pathways of these pesticides from pets to waterways are factored in, e.g., dogs swimming in rivers, and the contribution of cat spot-on treatments also considered, it is likely that pet-flea treatments will turn out to be the primary contributor.  As much of the current use of ectoparasiticides for dogs and cats is unnecessary, especially over the winter period, the veterinary profession needs to urgently re-consider its approach to preventative flea control."