Fleas and ticks can be a nightmare for any pet owner to manage. But a convenient treatment for these external parasites could come with more risks for the environment than we knew, scientists have just found.

Researchers in France studied the feces of cats and dogs administered certain antiparasitic medications known as isoxazolines. They continued to find some of the drugs in the pets’ poop even after their treatment had ended. They also concluded that essential, poop-loving bugs in the wild are likely being exposed to dangerous levels of these compounds via pest-treated pets.

“These findings emphasize the need for further research on environmental contamination and impact of veterinary parasiticides on nontarget species,” the researchers wrote in their paper, published Wednesday in Environmental Toxicology and Chemistry.

A convenient but possibly risky option

Isoxazolines are a relatively new type of antiparasitic medication, with the first drug of its kind approved in 2013.

These drugs quickly became a popular option among veterinarians and pet owners for several reasons. They can treat both ticks and fleas, are usually available as an easy-to-take pill, and provide a long-lasting effect (at least a month) that can prevent further infestations. One of the newest approved drugs on the market, Bravecto Quantum, can even work for up to a year, though it does have to be taken as an injection.

Impressive as isoxazolines are, some experts and health agencies have worried about the effect they could be having on unintended insects and other arthropods, since these drugs can seep into the environment through a pet’s feces, urine, and even hair. The European Medicines Agency (EMA) has recently called for a reevaluation of the environmental impact that flea and tick medications might have, for instance. They note that growing pet populations and increased use of these drugs could be raising environmental risks.

The researchers recruited 20 dogs and cats owned by veterinary students for their study. The pets were given one of four commonly used isoxazoline drugs as recommended for three months (fluralaner, (es)afoxolaner, lotilaner, and sarolaner), and the researchers periodically tested their poop for traces of each.

All the drugs had median half-lives ranging from 15 to 25 days, they found, though it differed depending on the species and specific drug. And two of the drugs (fluralaner and lotilaner) could still be detected in pets’ poop after the recommended treatment period was over.

The researchers also ran simulations on the potential risk posed by these drugs left behind in pet poop to dung-feeding insects in the wild, based on their results. They determined that in most scenarios, there was likely a real risk of high exposure to these drugs, particularly fluralaner and lotilaner.

A need for more study

These findings don’t yet confirm that isoxazolines are wreaking havoc on insects in the wild everywhere. But they do highlight the urgent need for more research to figure out just how dangerous they could be to innocent bugs in parks and other places where our pets regularly do their business.

“Our preliminary assessment suggests that pet ectoparasiticides may be detrimental to the environment and supports the conclusions from the EMA scientific opinion,” the researchers wrote.

Understanding these risks better might also help us mitigate them. In countries and regions where garbage is routinely incinerated, for instance, it might be beneficial to recommend that pet owners always throw out their pet’s poop in the trash during their flea and tick treatment, the researchers suggested as a potential idea.