Martin Whitehead MRCVS is calling on the profession to adopt a responsible use of parasiticides after a study he co-authored found UK rivers contaminated with fipronil and imidacloprid. 

'Potential role of veterinary flea products in widespread pesticide contamination of English rivers1, was carried out by Professor Dave Goulson and Rosemary Perkins MRCVS from the University of Sussex and co-authored by Martin (pictured right) and Wayne Civil from the Environment Agency. 

For the study, they looked at 3,861 samples taken from 20 rivers around the UK between 2016 and 2018. Fipronil was detected in 98% of the samples and imidacloprid in 66%. 

Currently, there are no environmental quality standards for fipronil or the compounds it breaks down into (fipronil sulfone or fipronil sulfide) or for imidacloprid in British surface waters.

The authors therefore used the acute and chronic toxicity limits for fipronil from a report from the Department of Environmental Toxicology at the University of California Davis2, and from Morissey et al (2015)3 for imidacloprid. 

They found that the average fipronil concentration across the rivers sampled by the Environment Agency 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. 

The paper, published in Science of the Total Environment, noted that the highest levels of pollution were found immediately downstream of wastewater treatment works, which the authors say supports the hypothesis that significant quantities of pesticide may be passing from treated pets to the environment via household drains.

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

Bathing of pets treated with spot-on fipronil flea products has been confirmed as a potentially important route to waterways for fipronil via sewers. The washing of hands, pet bedding or other surfaces that have come into contact with treated pets are potential additional pathways for entry to sewers.

Rosemary said: “We’ve identified a number of steps that can be taken to minimise or avoid environmental harm from pet flea and/or tick treatments. These range from introducing stricter prescription-only regulations, to considering a more judicious and risk-based approach to the control of parasites in pets, for example by moving away from blanket year-round prophylactic use."

Martin said: "The profession urgently needs to adopt ‘responsible use of parasiticides’ similar to the way it is adopting responsible use of antimicrobials. The VMD needs to strengthen the environmental assessment of pet pesticide products in the authorisation process, and they are currently considering this issue. The VMD should also collate and publish annual sales figures for these pesticides as they do for antimicrobials."

He added: "My veterinary hospital has never had a ‘pet health plan’ to provide year round flea products, because we believe that year-round, intensive treatment for almost all dogs and cats does not constitute responsible use of such powerful pesticides."


  1. Rosemary Perkins, Martin Whitehead, Wayne Civil, Dave Goulson, Potential role of veterinary flea products in widespread pesticide contamination of English rivers, Science of The Total Environment, 2020, 143560, ISSN 0048-9697,
  2. Bower, J.C., Tjeerdema, R.S., 2017.Water and sediment quality criteria report for Fipronil. Final report. Report prepared by theUniversity of CaliforniaDavis for the Central Valley regional water quality control board. Available at.
  3.  Morrissey, C.A., et al., 2015. Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: a review. Environ. Int. 74, 291303.

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