The banana is one of our least guilt-inducing snack foods, and it is easy to see why it’s the most popular fruit in the United States. It is a sweet-tasting source of fiber, potassium, B vitamins, and many other nutrients, packed in a handy, biodegradable wrapper. The average American eats an average of 28 pounds of this fruit each year—more than apples and oranges combined.
As with everything in life, however, there are caveats. Taking a closer look at the environmental implications of how bananas—and many other fruits and vegetables—are actually produced might give you ‘food for thought’ the next time you pass through the produce section of the supermarket.
The Cost to Costa Rica
Costa Rica is an ideal place to grow bananas. It has a warm, wet climate, and the local geology provides fields with natural drainage into waterways, reducing the need to construct extensive culvert systems. One of these waterways is the Rio Suerte. This river winds through one the nation’s most productive banana-growing regions, eventually arriving at the Tortuguero Conservation Area. Costa Rica’s economy derives a large chunk of its support from tourism and scientific research, and the biodiversity harbored in Tortuguero—which includes both Tortuguero National Park and the Barra del Colorado National Wildlife Refuge—is a significant ecological and economic asset to the small Central American nation.
Despite its environmental and economic importance, Tortuguero is in a vulnerable location. The Costa Rican soil “conveniently” allows run-off from fields to flow into Rio Suerte, and any substances in this effluvium are swept downstream towards Tortuguero, which is supposed to be a refuge for rare and unique tropical species.
The hazard here is very real, because banana plantations are heavily doused with pesticides. Costa Rica is ranked second in the world for intensity of pesticide use, applying an average of 52 kg of active ingredient to each hectare of land each year. The chemicals are sometimes spread from airplanes in close proximity to streams and rivers. In addition, there is very little oversight devoted to monitoring the disposal of over leftover chemicals and their containers. Costa Rica is a small country—just over 3/4 the size of West Virginia. On that small of a scale, it is hard to put large distances between key wildlife reserves or human settlements and commercial plantations. Chemical contamination is an ongoing public and environmental health concern in this region.
Costa Rica does have its reasons for being so heavy-handed with pesticides. Heavy rains frequently rinse the pesticides off the banana plants, leaving them vulnerable to insects until the chemicals are re-applied. The rain doesn’t dissolve the chemicals, though: it shunts them from croplands to natural waterways. These streams and rivers are home to many aquatic species, ranging from the microscopic critters that form the base of the food chain to the large fish consumed by both predators and local humans.
Due to the intermittent cascades of pesticide runoff into waterways, the concentration of toxins in the water can vary with the river’s flow strength, volume, and many other variables. This makes it difficult to gather precise data on overall contamination levels. To get around this problem, researchers can measure the intensity of pesticide exposure and assimilation in local wildlife directly by sampling the tissues of organisms living in the water.
The Case of the Spectacled Caiman
It is useful to collect samples from long-lived species, so the tissues represent the contamination load just from as many years as possible. It can also be valuable to sample a species that is fairly high in the trophic hierarchy (a more correct term for the “food chain”), because predators accumulate toxins from their prey animals, thus acting as indicators for contamination at several trophic levels. In places like Costa Rica, crocodilians are both long-lived and predatory, making them valuable as sentinel species for environmental contamination in aquatic communities. These toothsome animals are a little more intimidating than the proverbial “canary in a coal mine,” but they serve the purpose nonetheless.
One common crocodilian in eastern Costa Rica is the spectacled caiman (Caiman crocodilus). A team of researchers from Canada’s Institute of Ocean Sciences, led by Peter Ross, decided to focus in on this species as a sentinel for pesticide contamination in waterways. They recently reported their results in the scientific journal Environmental Toxicology and Chemistry.
Ross and colleagues sampled caimans from four connected Costa Rican waterways, including the Rio Suerte. They collected data from a total of fourteen caimans: six individuals were captured at sites within the “immediate influence” of commercial agriculture, and another eight were sampled from areas that were either far afield or upstream from these areas. The researchers had to find a caiman at night, grab the animal with either their hands or a noose, and then pull it into their boat for examination. They also restricted their sampling to individuals within a similar body size range, to avoid age-related variation in tissue contamination levels. It took the team three months to obtain data from fourteen individuals.
Once the researchers had a caiman in hand (literally), they took a variety of size measurements and classified its body condition, which was calculated using equations that relate skeletal length to body volume. They also took blood samples, which were sent back to British Columbia to be analyzed for a list of 70 different agricultural chemicals. The list included both legal substances and those that have been banned in recent decades (referred to as “legacy” chemicals). The caimans were then released, alive and well, although probably a little confused and a more than a little irritated.
Next, Ross and colleagues ran statistical analyses to assess relationships between caiman body dimensions, body condition, distance from the nearest pesticide source, and the pesticide concentrations found in each caiman’s blood. This allowed the team to explore three separate but related questions: 1) How much of the pesticide runoff from agricultural areas is being assimilated into animal tissues in the local waterways?; 2) Does pesticide load vary with distance from pesticide sources?; and 3) Does pesticide load significantly affect the caimans’ body condition?
The findings were sobering yet unsurprising. Lab analyses revealed that every single caiman, even the “upstream” individuals, had both legal and banned pesticides in its blood. In total, nine different pesticides were present. Seven of those are legacy substances, all of which were classified as “persistent organic pollutants” (POPs) by the Stockholm Convention, meaning that they hang around in the environment long after managers have stopped using them on crops. These POPs are metabolites of notorious substances such as DDT, which wreak havoc on endocrine function and interfere with reproduction and physical development. The other two substances found in caiman blood were pyrethroid insecticides, which are currently legal in Costa Rica and many other countries, despite ongoing concerns about their effects on human and animal health.
Although all of the caimans had detectable levels of pesticides in their blood, the six individuals captured in downstream watersheds close to agricultural areas had pesticide concentrations almost five times as high as upstream individuals: 6.03 ng/g lipid vs 1.3 ng/g lipid. This is a dramatic difference, and it indicates that croplands are very likely to be the main sources of the pesticides found in local spectacled caimans.
Caimans with higher pesticide concentrations didn’t differ in size from their less-contaminated kin, but they did exhibit significantly lower overall body condition. At this point it is unclear whether this was due to direct effects of pesticides on the reptiles’ physiology or to lower quality and/or abundance of prey in the more contaminated waterways.
By highlighting an ecologically important, charismatic predator whose tissues have been significantly contaminated pesticides, this study puts a scaly face on the long-lasting effects of chemicals applied to agricultural fields. Many of the substances containing the POP contaminants were phased out 20 years ago, and yet they persist in animals that weren’t even alive at the time they were applied. Meanwhile, Costa Rica continues to add an average of 52 kg of pesticides to each hectare of its land every year.
The Environmental Baggage of Healthy Foods
It would be unfair to single the banana out as uniquely problematic: it is not the only crop grown in that region of Costa Rica, so it may be unfortunate that the fruit was singled out in this study as the poster child for pesticide pollution. The problem itself is very real, though. We need to pay more attention to broader global food production practices, because many healthy foods carry “environmental baggage.” It may seem virtuous to eschew animal products in favor of soy lattes and veggie burgers, but soybean production is gradually erasing more and more of South America’s rainforests with each passing day. Coffee, for all of its perks, is a significant source of tropical habitat destruction and fertilizer contamination. Even the seemingly faultless organic salad isn’t innocent: it costs hundreds of calories of fossil fuel to move a single calorie of organic lettuce from California to a supermarket in another part of the country.
One of the take-home messages of this study is that the production of our “health food” may have decidedly unhealthy effects on the local wildlife and human populations that actually inhabit its source regions. This doesn’t mean that we should stop eating produce or other health foods, of course, not by a long shot. It simply presents the opportunity to increase market demand for food grown using more environmentally responsible practices.
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Anne-Marie Hodge, EGN’s Species Science Advisor, is currently a PhD student at the University of Wyoming in Ecology, and holds a Bachelor of Science in Zoology from Auburn University and a Master of Science in Biology from the University of North Carolina-Wilmington. While at Auburn, she established and served as president of Alabama’s first chapter of the Society for Conservation Biology. Anne-Marie’s research interests include community ecology, predator-prey dynamics, and conservation, with a focus on tropical carnivores. She has research experience in Mexico, Belize, Ecuador, and Kenya.