Pesticides commonly used as flea treatments for pets are contaminating English rivers

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pesticides in flea treatments
Photo: Олена Сушицьк – 123rf

Researchers from England have found widespread contamination of English rivers with two neurotoxic pesticides commonly used in veterinary flea products: fipronil and the neonicotinoid imidacloprid. The concentrations found often far exceeded accepted safe limits.

These chemicals are banned for agricultural use due to the adverse environmental effects, but there is minimal environmental risk assessment for pesticides used on domestic cats and dogs. This is due to the assumption that there are likely to be fewer environmental impacts due to the amount of product used.

But there is growing concern that this assumption may be incorrect. To investigate this, a team from the University of Sussex analysed data gathered by the Environment Agency in English waterways between 2016-18. They found that fipronil was detected in 98 per cent of freshwater samples, and imidacloprid in 66 per cent.

“Fipronil is one of the most commonly used flea products, and recent studies have shown that it degrades to compounds that are more persistent in the environment, and more toxic to most insects, than fipronil itself,” said Rosemary Perkins.

“Our results, showing that fipronil and its toxic breakdown products are present in nearly all of the freshwater samples tested, are extremely concerning.”

There are 66 licensed veterinary products containing fipronil in the UK, and 21 containing imidacloprid, either alone or in combination with other parasiticides. These include spot-on solutions, topical sprays and collars impregnated with the active ingredient.

The researchers—whose paper is published in Science of the Total Environment—found that the average fipronil concentration across the rivers exceeded chronic safety thresholds five-fold. The overall pollution levels in English rivers indicate that fipronil and its toxic breakdown products pose a high risk to aquatic ecosystems.

While, in most rivers, imidacloprid was found to pose a moderate risk, in seven out of the 20 rivers sampled there was a high environmental risk.

“Fipronil and imidacloprid are both highly toxic to all insects and other aquatic invertebrates,” Professor Dave Goulson said.

“Studies have shown both pesticides to be associated with declines in the abundance of aquatic invertebrate communities. The finding that our rivers are routinely and chronically contaminated with both of these chemicals and mixtures of their toxic breakdown products is deeply troubling.”

The paper notes that the highest levels of pollution were found immediately downstream of wastewater treatment works, supporting the hypothesis that significant quantities of pesticide may be passing from treated pets to the environment via household drains.

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