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For the study, which was funded by the charity Songbird Survival, researchers collected the nests of 103 blue and great tits, and tested them for the presence of 20 insecticides.
Fipronil, imidacloprid and permethrin were the main culprits, detected in 100%, 89.1% and 89.1% of the samples respectively.
Overall, a higher number of either dead offspring or unhatched eggs was found in nests containing a higher number of insecticides, higher total concentration of insecticides or a higher concentration of fipronil, imidacloprid or permethrin, which the authors say suggests contact exposure of eggs to insecticides in nest lining may lead to mortality and lower reproductive success.
The BVA responded by calling for more research and encouraging vets to work with clients to ensure responsible use of parasiticides.
BVA President Elizabeth Mullineaux said: “Parasiticides play an important role in preventing and treating parasites in animals, which if left unaddressed can lead to bigger health and welfare issues in both animals and people.
"But it’s important they are used responsibly, and this work from the University of Sussex and SongBird Survival highlights the need for more research into how parasiticides affect the environment and wildlife and the associated risks.
“Rather than blanket use, we strongly encourage vets and owners to take a risk-based approach to prescribing or recommending these medicines, reflecting an animal’s exposure to parasites."
Reference
'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."
References
Morrissey, C.A., et al., 2015. Neonicotinoid contamination of global surface waters and associated risk to aquatic invertebrates: a review. Environ. Int. 74, 291–303. https://doi.org/10.1016/j.envint.2014.10.024.