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We Americans love bananas. Each year, we eat more bananas than any other fruit. And most banana growers make heavy use of pesticides. For example, one-third of all the pesticides used in Costa Rica, one of the major suppliers of the world's bananas, is on banana plantations.

And now, a new study from Costa Rica suggests that these pesticides may be hurting wildlife. As NPR's Rhitu Chatterjee reports, the chemicals are winding up in the bodies of crocodiles.

RHITU CHATTERJEE, BYLINE: There's a reason why banana farmers use a lot of pesticides.

CHRIS WILLE: Banana plantations are in the tropics, where there are a lot more kinds of pests and in abundance.

CHATTERJEE: That's 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. And it's not just insects they're trying to control, he says. There are fungal diseases, too.

WILLE: When you see pictures of airplanes spraying banana farms, they're spraying for an airborne fungal disease called Black Sigatoka, which can devastate a plantation in a matter of a week or so.

CHATTERJEE: Many of Costa Rica's banana plantations are in the remote northeastern region among streams, canals and rainforests. That's where Paul Grant, a wildlife biologist at Stellenbosch University - in South Africa - went, to investigate whether pesticides are hurting local wildlife.

PAUL GRANT: In the past, I have witnessed - and other locals have pointed out - that there have been massive fish kills as a result of pesticide exposure in high levels.

CHATTERJEE: Grant wanted to know if 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 because a bony ridge between its eyes makes it look like its wearing eyeglasses. These caimans live in the Tortugero Conservation Area, which is just downstream from the banana farms.

GRANT: Because they're long lived and they're at the top of the food chain, a lot of the pesticides will kind of wind up at the top.

CHATTERJEE: He collected blood samples from 14 adult caimans; some that lived closer to plantations and others further downstream, in cleaner waters. He and his colleagues analyzed the blood samples for 70 different pesticides. What they found concerned him. The samples contained nine pesticides, two of which are currently in use and...

GRANT: Seven of which were historic persistent organic pollutants.

CHATTERJEE: These are pesticides like DDT, dieldrin and endosulfan, chemicals that have been banned for nearly a decade but persist in the environment and build up in the bodies of animals. Peter Ross is an environmental scientist at the University of Victoria in British Columbia, and also an author on this study. He says even though the overall levels of the pesticides were modest, there was some indication that they were causing harm.

PETER ROSS: What was revealing to me was the fact that the caiman that were near banana plantations had not only higher concentrations of most of the pesticides that were detected, they were in a poorer state of health relative to the caiman that were in the more pristine, remote areas.

CHATTERJEE: Ross and his colleagues have published their findings in the latest issue of the journal Environmental Toxicology and Chemistry. Chris Wille, of the Rainforest Alliance, says there's an important lesson here.

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

CHATTERJEE: Especially as the demand for bananas has been growing worldwide, and plantations are moving towards more intensive methods of cultivation.

Rhitu Chatterjee, NPR News.

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