Pesticides that are used to treat cats and dogs for fleas are causing ‘widespread contamination’ of English rivers, a new study warns.
Scientists have found two neurotoxic pesticides – fipronil and imidacloprid – in river samples in concentrations that ‘far exceed accepted safe limits’.
Both chemicals are banned from agricultural use due to the toxic effects on insects, birds, fish, mammals and other creatures.
But they are still used in veterinary flea products and are applied to millions of dogs and cats in Britain.
The experts analysed data gathered by the Environment Agency based on samples taken from 20 English waterways between 2016 and 2018.
They found that fipronil was detected in 98 per cent of freshwater samples, while imidacloprid was found in 66 per cent.
The highest levels of pollution were found immediately downstream of wastewater treatment works, suggesting they’re passing from treated pets to the environment via household drains.
Researchers at the University of Sussex have found widespread contamination of English rivers with two neurotoxic pesticides commonly used in veterinary flea products – fipronil and the neonicotinoid imidacloprid
‘Fipronil and imidacloprid are both highly toxic to all insects and other aquatic invertebrates,’ said study author Professor Dave Goulson at the University of Sussex.
‘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.’
According to the Veterinary Medicines Directorate (VMD), who funded the research, 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.
Graphic showing how the chemicals get into English waterways. After the pets receive treatment, the chemicals can wash off into bathwater and leak from wastewater treatment plants into nearby waters, killing wildlife
While some of these products can be purchased only with a veterinary prescription, others can be bought without a prescription from pet shops, supermarkets, pharmacies and online.
Many pet owners receive year-round preventative flea and tick treatment from their vet practice through healthcare plans.
Researchers say pets treated with spot-on fipronil flea products pass on the chemical into waterways, by way of the sewers, after they’ve been bathed.
The washing of hands, pet bedding or other surfaces that have come into contact with treated pets are also potential pathways for entry to the sewers, as is rainfall wash-off.
But both chemicals have high toxicity towards a wide range of invertebrates and a high level of solubility in water.
Researchers took 20 water samples from around England, including five less than 1.2 mile (2km) from wastewater treatment works – Arun in West Sussex, a stream near Southborough in Kent, River Douglas near Wanes Blades Road in Lancashire, Sincil Dyke near Lincoln and Wyke Beck in Yorkshire.
Researchers detected fipronil in all 20 sites sampled between 2016 and 2018, and in 1,303 out of 1,322 individual samples.
Bathing of pets treated with spot-on fipronil flea products has been confirmed as a potentially important route to waterways for fipronil
The average fipronil concentration across the rivers sampled exceeded chronic safety thresholds five-fold.
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.
From the 20 sites, imidacloprid had an average concentration below its chronic toxicity limit – however, seven out of 20 sites exceeded that limit
Sites immediately downstream of wastewater treatment works had the highest levels of fipronil and imidacloprid.
Fipronil is a broad use insecticide that belongs to the phenylpyrazole chemical family and is used in spot-on pet care products for fleas and ticks, as well as liquid insect control products, effective on ants, beetles, cockroaches and other insects.
Fipronil has a history of very limited agricultural use prior to its ban for use on crops by the European Union in 2017.
That year, the chemical had contaminated around 700,000 eggs imported from the Netherlands to the UK, which had to be recalled by leading supermarkets including Asda and Waitrose.
The highest levels of pollution were found immediately downstream of wastewater treatment works. Pictured, purification tanks of modern wastewater treatment plant in Leeds
Residues of imidacloprid and fipronil may still be present on imported food, although these amounts are likely to be very low, the University of Sussex team said.
According to the experts, once fipronil breaks down its byproducts are even more damaging to the environment than fipronil itself.
‘Our results, showing that fipronil and its toxic breakdown products are present in nearly all of the freshwater samples tested, are extremely concerning,’ said study author Rosemary Perkins at the University of Sussex.
‘The use of pet parasite products has increased over the years, with millions of dogs and cats now being routinely treated multiple times per year.’
Imidacloprid, meanwhile, is a type of neonicotinoid – a class of substances chemically similar to nicotine and used as insecticides.
Imidacloprid and other neonicotinoids are known to be responsible for plummeting bee numbers around the world, causing brain damage that affect their ability to forage for nectar and pollen.
Fipronil was the subject of a recent controversy when the chemical was found to have contaminated eggs imported from the Netherlands
As a result, the outdoor use of imidacloprid was banned by the European Commission in 2018.
Despite the chemicals’ prevalence in pet flea and tick treatments, there is minimal environmental risk assessment when they’re used on domestic cats and dogs.
‘We’ve identified a number of steps that can be taken to minimise or avoid environmental harm from pet flea and/or tick treatments,’ said Perkins.
‘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.
‘We’d recommend a re-evaluation of the environmental risks posed by pet parasite products, and a reappraisal of the risk assessments that these products undergo prior to regulatory approval.’
The research has been published in Science of the Total Environment.