Two popular pet flea and tick products contain toxic “forever chemicals” linked to significant human health issues, according to testing by a nonprofit watchdog group.

Seresto flea and tick collars and Frontline topical treatments each tested positive for PFAS, a class of more than 9,000 man-made chemicals linked to cancer, liver damage and lower birth weights even at extremely small levels. 

Flea and tick products are designed to release pesticides that persist for weeks or months at a time, staying on the fur of an animal. Humans can often be exposed to the pesticides by petting, sleeping with and sitting on the same surfaces as pets. These products have been linked to hundreds of adverse incidents involving humans. 

But until this testing, pet products were not known to contain PFAS.

“This shows these chemicals are a constant presence in our house, on the rug, on the furniture or on the bed or wherever a pet goes,” said Kyla Bennett, a scientist and attorney formerly with the Environmental Protection Agency.

The testing was conducted by an independent lab and paid for by Public Employees for Environmental Responsibility, a nonprofit organization of current and former government employees working to hold their agencies to a higher standard. In recent years, PEER has found the EPA to be negligent in testing for PFAS and has decided to undergo its own testing of products, said Bennett, the group’s science policy director.

The testing found:

  • Frontline Plus for Dogs, one of many topical treatments used to help control flea and ticks on pets sold under the brand name Frontline, contains 2,390 parts per trillion of four different PFAS.
  • Seresto flea and tick collars contain 250 parts per trillion of a long-chain PFAS, which means the chemical is more likely to persist. 

The EPA has recommended a 70 parts per trillion lifetime limit for PFAS in drinking water, though it has not yet set formal regulations. Scientists and environmental groups have called for limits as low as 0.1 ppt, and many states have set their own standards for PFAS in drinking water.

[Read more: Popular flea collar linked to almost 1,700 pet deaths. The EPA has issued no warning.]

The EPA said PFAS are not ingredients in the products. This means the chemicals somehow leach into the collars somehow, either through the container they are stored in or another mechanism, experts said.

The agency added it has received the group’s data and is reviewing it as part of a larger investigation into PFAS contamination in pesticide products. It said it will work with Elanco, the maker of Seresto, and Boehringer Ingelheim, the maker of Frontline, on “next steps if needed.”

“More broadly, Administrator (Michael) Regan has called on the agency to build on its ongoing work to better understand and ultimately reduce the potential risks caused by PFAS chemicals,” the statement said. 

“Over the past few years, science has progressed rapidly, and the agency must move forward with actions that are based on this new science and a better understanding of the complex challenges,” the statement continued. “EPA’s research on PFAS is helping to deepen the agency’s understanding of these chemicals so that we can take the right steps to continue reducing risks to public health.”

Keri McGrath, a spokeswoman for Elanco, said the PEER test was on one Seresto collar, and the finding was just above the detectable limit of the testing method. McGrath pointed out that many household substances, including “fast food containers, pizza boxes and candy wrappers,” contain PFAS.

Mark Bixler, a spokesman for Boehringer Ingelheim, said the “health and safety of pets, their owners and the environment, as well as the integrity of our products, have always been and will always be our top priorities.” Bixler said the products have been approved in more than 150 countries and have performed safely since they were introduced in 1994.

The EPA asked states to stop spraying another pesticide, called Anvil 10+10, after PEER testing showed it had 250 parts per trillion of a PFAS — the same level as the Seresto collar that was tested. The agency determined the pesticide’s use to control mosquitoes risked contaminating drinking water, according to the Boston Globe. It was later determined that the PFAS was likely being leached into the pesticide from its storage containers. 

A February 2020 peer-reviewed study found that cats and dogs in New York have levels of PFAS in their feces that are above the minimal level of concern. 

Kurunthachalam Kannan, a professor of pediatrics and environmental medicine at New York University and co-author of that study, said that, while some pet foods have been shown to have PFAS, the study showed that pets have higher levels of PFAS in their feces than expected. 

“Pets are excreting more than what they are eating. It means there are other sources,” Kannan said. “Now we see that sources like this can contribute to the exposure.”

Kannan said that it is unclear at what level PFAS has an effect on pet health, but low levels of the chemicals have been linked to liver damage and cancer in humans. Kannan said high levels in pets is likely an indicator for high levels in humans.

Multiple studies have also shown that active ingredients in pet collars can end up in nearby water sources. The pesticides imidacloprid and fipronil have contaminated rivers in England because of pet treatments, according to researchers at the University of Sussex.

Bennett said, even in the  small New England town where she lives, there are likely thousands of dogs wearing the collars or being treated with the spot-on treatments. Each time those dogs are washed, she said, the chemicals have the potential to contaminate water supplies.

PFAS compounds are found in many products, so it was not surprising to see they are in pet flea and tick treatments, said Linda Birnbaum, former director of the National Institute for Environmental Health Sciences and the National Toxicology Program at the U.S. Department of Health and Human Services.

“They’re turning out to be everywhere,” Birnbaum said. 

Birnbaum said the chemicals, even at levels like those found in the collars, pose a risk to humans. Birnbaum said an investigation should be launched into why they’re in the products and what can be done to prevent it.

“These are not nice chemicals,” Birnbaum said. “They’re all very persistent. They’re going to build up in the body, so why are we exposing ourselves?”

Heather Stapleton, a professor of environmental sciences and policy at Duke University, said she is not surprised to see the chemicals in pet products because they have been found in other pesticide products. 

Stapleton said she would like to see much more testing of the products in order to make a determination about their safety, but the presence does raise concerns for pets and pet owners.

In recent months, the Seresto collar has been the subject of a Congressional inquiry and an EPA investigation after Investigate Midwest and USA TODAY reported the EPA had received more than 75,000 reports of adverse incidents, including about 1,700 pet deaths, related to the collar.

Frontline treatments have also had a large number of adverse incidents, EPA data show.

Scott Belcher, a research professor of toxicology at North Carolina State University, said the levels are so low that they likely aren’t contributing to adverse incidents in pets. 

“I would not be at all concerned about PFAS exposure compared to the impacts of the pesticide,” he said. “That’s a pesticide toxicity, not a PFAS toxicity.”

Still, the pet products are yet another avenue of potential exposure to these toxic chemicals.

“It’s one more place where we’re using PFAS where we probably shouldn’t,” Belcher said.

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