ENGLISH RIVERS — A study published Thursday by ecologist Matt Shardlow found that toxic chemicals from pet flea treatments are contaminating rivers, parks, and conservation areas across England and harming aquatic life, birds, and pollinators. The analysis identified contamination in rivers, sites of special scientific interest, and National Parks, including all the main rivers entering the Broads in Norfolk.

The study focused on fipronil and imidacloprid, which are banned for use as pesticides but remain in liquid flea treatments for cats and dogs. According to the Environment Agency, imidacloprid is the chemical with the highest risk to human health in English waters.

Average levels of fipronil and imidacloprid in English rivers were high enough to reduce aquatic life, and in one fifth of tested cases, chemical levels were sufficient to cause a 30% reduction in associated bird populations. Natural England is concerned that dragonfly numbers in the Broads in Norfolk have declined by 90%.

Earlier research found that songbird feathers were widely contaminated with fipronil and imidacloprid at levels that can damage their brains and kill unborn chicks. A previous study also found that high levels of pesticides in pet fur used by parent birds to line their nests were killing chicks. Shardlow carried out one of the first studies into the environmental impact of pet flea treatments nine years ago.

Topical flea and tick treatments applied to dogs and cats are the main route through which the chemicals enter the environment. They can enter the sewage system when treated animals or contaminated clothing or bedding are washed, and can also reach waterways when dogs swim, when pets rub against vegetation, or when they shed fur outdoors.

"The level of new alarming information showing the scale of damage that is being done by these chemicals is stark," Shardlow said. "We are seeing not just impacts in rivers but in public parks where dandelions were so heavily polluted that it is likely to harm caterpillars and pollinators."

Shardlow called on the government to undertake an environmental risk assessment of pet flea treatment chemicals, and for the Veterinary Medicines Directorate to review, suspend, and ban flea treatments containing fipronil and imidacloprid. "The government has simply not done what a proper environment regulator should do and look into the new evidence," he said.

The government announced an eight-week consultation on banning over-the-counter sales of flea treatments for cats and dogs in the UK. "We recognise the benefits of fipronil and imidacloprid and the role they play in protecting pets and people from parasites and the diseases they carry. However, these substances are entering our watercourses and could be contributing to wider environmental impacts. We want to hear as many perspectives as possible in this consultation to help us maintain appropriate market availability while also protecting our animals and the environment," a Veterinary Medicines Directorate spokesperson said. "We are committed to restoring nature and cleaning up our rivers whilst upholding the highest animal welfare standards," a Department for Environment, Food and Rural Affairs spokesperson said.