Scientists warn pet flea and tick treatments are polluting UK rivers

Scientists have warned that flea and tick treatments used for our pet dogs and cats contain chemicals that are entering UK freshwaters including rivers and ponds.

A briefing paper by Imperial College London researchers showed that many of these parasite treatments contain a chemical in a class called neonicotinoids. These chemicals have been banned for agricultural use on crops as evidence shows they impact bees and other pollinating insects important for our food supply.

The researchers say this evidence points to an urgent need to review risk assessments and prescribing practices for these chemicals. reports these flea treatments were still widely sold as pet parasiticides as it was thought they were not able to reach the environment in large enough doses. However, new measurements of invertebrates and of river water in the UK instead show they are present in urban environments, and often in concentrations that are known to harm aquatic life in lab experiments, which could cause knock-on effects on the wider ecosystem.

The team considered the two main pesticides included in flea and tick treatments: the neonicotinoid imidacloprid and the related chemical fipronil. There are 138 pet parasiticide products currently authorized in the UK that contain imidacloprid and 396 that contain fipronil.

According to The Times, researchers at Imperial College London reviewed 160 scientific papers on the impact on aquatic ecosystems of imidacloprid.

Imidacloprid and fipronil are powerful killers of invertebrates such as insects. It was found that one monthly flea treatment for a large dog contains enough imidacloprid to kill 25 million bees.

A dog scratching herself (image: Rachel Claire:

Andrew Prentis, Visiting Fellow in the Grantham Institute at Imperial College London 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,” Prentis added.

The Environmental Agency monitoring data also shows that when detected, imidacloprid is at concentrations where risks to freshwater species are expected (i.e., moderate to high risk) in 52% of cases.

Many of the UK’s estimated 25 million dogs and cats are treated with parasiticides multiple times through the year, with some products recommending monthly doses. Some of these require a prescription, while others are available over the counter.

Once applied, these treatments are absorbed by the body, remaining in the skin, hair, and excretions. The chemicals therefore may reach natural waterways through household wastewater and combined sewer overflows: the main routes are believed to be through owner hand washing, and people washing their pets and their pet’s bedding and clothes.

Rhys Preston-Allen, from the Department of Life Sciences at Imperial, said, “Ultimately, this report brings into question whether the balance has shifted in such a way that the environmental harm caused by these chemicals now outweighs the benefits to pets and owners.”

Preston-Allen continued, “What is clear is that this is a complex issue that requires collaborative action from regulatory bodies, scientists, vets, and consumers alike, to effectively limit the environmental impact of these chemicals. We all have a part to play in this.”

“Some solutions are common-sense, such as only prescribing and using parasiticides when a pet is afflicted by fleas and ticks rather than treating healthy animals,” Preston-Allen added. “Others are more practical, such as increasing emphasis on safe disposal of the products when they are used. With every new piece of evidence, there is also a growing willingness to reassess the regulation of these chemicals, so, I have faith that things are moving in the right direction.”

A 2021 study by Transparency Market Research found that the worldwide flea and tick product market has an estimated value of USD 5.8 billion.

Pet parents should speak with their vet regarding treatment of fleas and ticks and should ask about all forms of treatment available, including natural non-toxic treatments and prevention.

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