Pesticide concentrations are higher in caimans near banana plantations than those farther downstream.
A spectacled caiman, Caiman crocodilus, sits partially submerged in water. Pesticides are threatening the Costa Rican caiman population.
Photograph by John Cancalosi, National Geographic
Published September 30, 2013
New research from the journal Environmental Toxicology and Chemistry found that spectacled caimans (Caiman crocodilus) near banana plantations were significantly thinner, and had higher pesticide concentrations in their blood, than caimans in more remote locations. (Watch a video about banana farms in Costa Rica.)
"The animals are very, very thin—about 50 percent thinner than those away from the plantations," said study co-author Peter Ross, an aquatic ecotoxicologist and associate professor at the University of Victoria in British Columbia.
It’s unclear whether the pesticides are directly toxic to the caimans or are impacting their health indirectly by diminishing the quality and abundance of their food supply.
Ross thinks the latter scenario is more likely given the moderate pesticide concentrations he and his colleagues found. Since all of the pesticides detected were insecticides, the chemicals could be knocking out the bottom of the food chain. This would affect the fish that eat the insects, resulting in caimans having to search farther for food and use more energy to try to find the few fish that remain.
A Banana Bounty
With its warm temperatures, bountiful rainfall, and good soil, Costa Rica is a prime location for banana production. As a key export, bananas play an important role in the nation’s economy. In 2011, Costa Rica exported 2 million tons (1.9 million metric tons) of bananas, valued at over $700 million.
A banana plantation in the lowlands of eastern Costa Rica. Pesticides from plantations like this may be hurting the local caiman population.
Photograph by Buddy Mays, Alamy
As demand for the fruit increases, so does pesticide use. In the last two decades, pesticide use in Central America has doubled. Costa Rica ranks second in the world for intensity of pesticide use; and bananas, which lack the genetic diversity to fight off pests, receive some of the heaviest doses of any crop in the world.
Lack of infrastructure and enforcement regulating the use of these chemicals have contributed to environmental contamination. And the country’s frequent heavy rains wash the pesticides from target areas such as banana plantations and into nearby waterways.
In the northeast region of Costa Rica, the chemicals from the banana plantations appear to be winding their way down the Rio Suerte river (map) and into the Tortuguero Conservation Area, one of the most important wilderness areas in the country. This species-rich area provides critical habitat for many organisms on the IUCN Red List, including the spectacled caiman.
Caiman are ideal markers for the health of the ecosystem due to their abundance, longevity, and role as a top predator, said Paul Grant, lead study author and a doctoral candidate at Stellenbosch University in South Africa. Any habitat disturbances or stresses are reflected in caiman populations, and are thus easily observed. (Watch exclusive video of a jaguar killing a caiman.)
Grant and colleagues collected blood samples from 14 caiman and analyzed the samples for 70 current-use and legacy pesticides and breakdown products. Of the nine pesticides detected in caiman blood, seven were listed as persistent organic pollutants and banned under the Stockholm Convention adopted in May 2001.
"The reason the Stockholm Convention exists is because these types of chemicals are readily transported through the air and can end up in remote, pristine environments," said Ross.
The presence of pesticides in the caimans’ blood wasn’t surprising to Ross. "Wherever we look in the world, we run into pesticides and industrial chemicals," he said.
But while the pesticide concentrations researchers detected were moderate, the detrimental effects observed in caiman may signal consequences for the entire ecosystem. Pesticide exposure has been linked to disease susceptibility, reproductive failure, developmental abnormalities, and die-offs.
We don’t know the level at which those multiple pesticides start to be a problem for the plants and animals in an area, said Grant, or how sensitive each organism will be to varying levels of the chemicals.
The fact that caiman are being impacted indicates that other aquatic organisms are going to be affected as well, he added. "There’s fairly strong evidence that pesticides, whether it’s indirect or directly, are eroding caiman habitat."