Ponds contaminated with harmful pet parasite treatments
Some ponds tested for over 20 times the threshold harmful for wildlife.
A study led by Imperial College London has revealed the contamination which dogs can cause by swimming in ponds.
Researchers discovered high levels of the pesticides imidacloprid and fipronil in several ponds at Hampstead Heath where dogs were permitted to swim.
Imidacloprid and fipronil are pesticides found in common flea and tick treatments used as a preventative measure on both dogs and cats. They were banned for agricultural use in 2018 due to their toxicity to bees and other insects.
However, there is now increasing concern that their use on pets is leading to environmental pollution, with these chemicals reaching the environment through household wastewater and dogs swimming in natural waters.
To investigate the impact that dog swimming has on environmental pollution, the team studied six ponds and six connecting streams in London’s Hampstead Heath. Hampstead Heath is known to have good biodiversity and is home to many rare and threatened species.
Researchers, including scientists from Imperial College London and the Royal Veterinary College, tested three ponds which dogs were allowed to swim in, three they were not, and the streams which connected to them.
In the ponds where dogs were permitted to swim, water analysis revealed the average concentrations of imidacloprid and fipronil to be 309 ng/L (nanograms per litre) and 32 ng/L respectively. This is over 20 times the thresholds recognised as harmful to invertebrate wildlife.
Where dogs were not permitted to swim, however, water analysis detected no imidacloprid or fipronil.
To assess how well the dangers of parasiticide contamination were understood, the team followed this up with a survey of 101 dog owners who had brought their dogs to Hampstead Heath.
The survey revealed that 86 per cent did not know that parasiticides could cause environmental harm. A third of respondents were also unaware that many parasiticides warn that dogs should not swim or be washed within a few days of treatment.
However, 94 per cent said they believed that protecting nature should be an important consideration when choosing treatments.
Lauren Yoder, from the Royal Veterinary College, said: "Dog owners can play an important part in reducing the overall impact on the water that dogs enjoy by checking if they really need to use these products.
“If more owners moved to a 'when needed' approach, then this parasiticide pollution could be reduced."
The full study can be found in the journal Science of the Total Environment.
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Veterinary practices are being urged to help owners safely dispose of any unused and expired pet medicines - not just antibiotics - during November's Animal Medicines Amnesty. 
