Many dog owners are unaware that treatments for fleas and ticks can harm aquatic life, indicating a need for greater awareness regarding this issue.
A recent study on Hampstead Heath indicates that ponds where dogs are permitted to swim have elevated levels of two pesticides that are detrimental to invertebrate ecosystems.
The pesticides in question, imidacloprid and fipronil, are commonly utilized as treatments for fleas and ticks on dogs and cats, typically applied through ‘spot-on’ treatments and flea collars. Notably, these chemicals were banned for agricultural use in 2018 due to their harmful effects on bees and other vital insects.
These treatments are being used more frequently as preventive measures—sometimes applied as often as once a month. Recent research has raised alarms about the environmental impact of these chemicals making their way into natural water systems through household wastewater and dogs swimming in areas like rivers and ponds.
A new study published today in the journal Science of the Total Environment has shown that water can become contaminated when dogs swim, as the chemicals rinse off their fur.
This research was conducted by scientists from Imperial College London, the University of Sussex, the London School of Hygiene and Tropical Medicine, along with the Royal Veterinary College, in partnership with the Heath & Hampstead Society and the City of London Corporation.
Dr. Leon Barron, a co-leader of the study from the School of Public Health at Imperial, stated, “This research contributes to the mounting evidence that could inspire changes in how pet treatments are prescribed and the advice provided to pet owners.
“Since these products are readily available in supermarkets without any restrictions, it’s crucial to inform dog owners about the potential risks associated with preventive use, which might lead to serious problems, such as environmental pollution and pest resistance.”
Lauren Yoder, the study’s lead author from the Royal Veterinary College, emphasized, “Dog owners can significantly mitigate the effects on the water bodies their pets enjoy by evaluating whether these treatments are really necessary. By adopting a usage-only-when-needed approach, we can minimize pesticide pollution.”
Concerning levels
Hampstead Heath, with its expansive 800 acres of woodlands, meadows, and ponds, serves as a biodiversity haven in central London, housing numerous rare and endangered British species. Invertebrates, including insects, play vital roles in our environment, such as maintaining clean water, and are crucial food sources for local birds and bats. The ponds support a rich variety of insects like dragonflies, showcasing impressive biodiversity.
The research team examined three ponds where dogs swim, three where they are prohibited, and six streams that feed these ponds to pinpoint any other potential sources of contamination.
In the ponds allowing dogs to swim, average levels of imidacloprid and fipronil were found to be 309 ng/L (nanograms per liter) and 32 ng/L, respectively—both over 20 times higher than the levels deemed harmful to invertebrate wildlife.
No traces of imidacloprid or fipronil were detected in the other ponds. Some contamination was found in the streams connecting to the ponds, but additional analysis indicated it was not linked to urban wastewater, suggesting that dogs were the only source.
Dr. Barron mentioned, “While the levels of these chemicals in the ponds were alarmingly high, fortunately, they did not significantly impact the broader water systems downstream from Hampstead Heath. Typically, the main sources of these parasite-related chemicals in rivers stem from our homes and streets through wastewater.”
Previous studies by the team found that London’s waterways were extensively polluted with these chemicals from wastewater releases, and the situation became worse in some areas during the pandemic.
Minimizing risks
The study also involved surveying 101 dog owners who visited the Heath, revealing that 86% were unaware of the environmental risks posed by these chemicals, while 94% indicated that protecting nature was an essential factor in their purchasing decisions.
A third of respondents were also unaware of the manufacturers’ advice advising against allowing dogs to swim or be washed within days of spot-on treatments. However, research suggests that these compounds may wash off for longer than recommended.
More than half of those surveyed preferred using tablet-based treatments instead of topical chemicals. There is limited information regarding the fate or impacts of these oral parasiticides, highlighting the need for further research to assess their risks.
Dr. Tilly Collins, a co-author from the Centre for Environmental Policy at Imperial, stated, “While swimming is beneficial for dogs, visiting such beautiful locations also promotes fitness and well-being for their owners. We shouldn’t prevent dogs from swimming in open areas, but instead, we should work on minimizing risks. This includes offering more comprehensive advice so pet owners can make informed choices.”
Co-author Dr. Rosemary Perkins, a veterinarian from the University of Sussex, added, “Many veterinary organizations discourage blanket preventive treatments for pets, yet this approach persists, particularly through subscription pet health plans. Pet parasiticides are highly toxic to the environment, and we’re only starting to grasp their ecological implications.
“It’s vital to equip pet owners with better information about the risks posed and provide alternatives to continuous treatment, such as the possibility of monitoring and treating only when necessary.”
