Hampstead Heath ponds where dogs swim contaminated with pesticides - Imperial College London

Most dog owners didn’t know that flea and tick treatments are dangerous to aquatic life, suggesting more awareness could ease the problem.

A study on London's Hampstead Heath shows that ponds where dogs are allowed to swim contain levels of two pesticides harmful to invertebrate life.

These pesticides, imidacloprid and fipronil, are used as parasite treatments for flea and tick infestations in cats and dogs, using ‘spot-on’ formulas and flea collars. This is despite these chemicals being banned for agricultural use in 2018 due to their toxicity to bees and other important insects.

These treatments are increasingly used prophylactically – to prevent fleas and ticks – with doses applied as frequently as monthly. Recent studies have raised concerns about the level of these chemicals reaching the natural environment through household wastewater and dogs swimming in waterways, such as rivers and ponds.

Now, a study published in the journal Science of the Total Environment has confirmed that swimming dogs can contaminate the water as the chemicals wash off their fur.

The study was carried out by researchers from Imperial College London, the University of Sussex, the London School of Hygiene and Tropical Medicine, and the Royal Veterinary College, in collaboration with the Heath & Hampstead Society and the City of London Corporation.