Americans love bananas. Each year, we eat more bananas than any other fruit. But banana growers use a lot of pesticides and those chemicals could be hurting wildlife. As a new study shows, the pesticides are ending up in the bodies of crocodiles living near banana farms in Costa Rica, where many of the bananas we eat are grown.

Of course, there’s a reason why banana plantations rely heavily on pesticides. For one, banana trees are particularly susceptible to infestations, says Chris Wille, the chief of sustainable agriculture at the nonprofit Rainforest Alliance. He works with banana growers to help them reduce the amount of pesticides they use.

Second, most plantations are in the tropics, “where there are a lot more kinds of pests and in abundance,” he says.

And insects aren’t the only problem there. There are worms and fungi, too.

“When you see pictures of airplanes spraying banana farms, they’re spraying for airborne fungal disease called Black Sigatoka, which can devastate a plantation in a matter of a week or so,” says Wille.

Many of Costa Rica’s banana plantations are in the remote northeastern region, at the headwaters of the Rio Suerte. The area is full of streams and canals, flowing past the banana farms and into protected rain forests that are part of the Tortuguero Conservation Area.

Paul Grant, a wildlife biologist at Stellenbosch University in South Africa, went there to investigate whether pesticides are hurting local wildlife.

“In the past, I have witnessed and a lot of the locals have pointed out that there have been massive fish kills as a result of pesticide exposure in high levels,” says Grant.

He wanted to know whether these pesticides are also ending up in animals that eat the fish. In particular, he was interested in a small crocodile called a spectacled caiman (so named because a bony ridge between its eyes makes it look like it’s wearing eyeglasses). These caimans live in the Tortuguero Conservation Area, which is just downstream from the banana farms. The animal is considered a threatened species by the International Union for Conservation of Nature.

Grant wanted to test caimans because they are long-lived animals and are top predators in the ecosystem. “A lot of the pesticides will wind up at the top of the food chain,” he says.

He collected blood samples from 14 adult caimans. Some of the animals lived closer to plantations and others farther downstream, in more remote, pristine areas.

He and his colleagues analyzed the blood samples for 70 different pesticides. The results concerned him.

The samples contained nine pesticides, of which only two are currently in use. The remaining seven are “historic organic pollutants,” says Grant.

These are pesticides like DDT, dieldrin, and endosulfan chemicals that have been banned, some of them for nearly a decade. But they persist in the environment and build up in the bodies of animals.

These chemicals are also found in significant levels in all sorts of aquatic mammals, including crocodiles in the U.S. and whales and seals in different parts of the world.

The overall levels of pesticides in the Costa Rican caimans in comparison were modest, says Peter Ross, an environmental scientist at the University of Victoria in British Columbia, also an author of this study.

Still, he says there was some indication that the chemicals may be harming the caiman.

“What was revealing to me was the fact that the caiman that were near the banana plantations had not only higher concentrations of pesticides, but also they were in a poorer state of health relative to the caiman in more pristine, remote areas,” says Ross.

Ross and his colleagues have published their findings in the latest issue of Environmental Toxicology and Chemistry.

There’s an important lesson here, says Wille of the Rainforest Alliance.

“You know, we’re now reckoning with the problem left by past use of highly toxic, highly persistent pesticides,” he says. “So, what plantations must avoid now is leaving similar toxic legacies for the next generation to deal with.”

Especially as the demand for bananas has been growing worldwide, and farms move toward more intensive methods of cultivation.