Study: More than half of Florida's manatees have the herbicide glyphosate in their bodies

If you’ve seen a manatee lately – surfacing in a ring of river water, basking in their namesake park in Lee County or drifting the Gulf – odds are the creature has herbicide coursing through its veins.

To the list of woes plaguing the warm-blooded mammals, already dying in droves from red tide, boat collisions, habitat loss and scarce food, a paper released last week adds glyphosate.

Researchers found the weed-killer, the world’s most-used pesticide, in more than half of all Florida manatees the study sampled. Nearly ubiquitous in Florida waters, the controversial substance is one of the go-to weapons in land managers' and homeowners' arsenals for combatting weeds. In 2019, a California jury ruled it was a substantial factor in a California man's cancer, in a lawsuit called a bellwether for hundreds of others waiting to be tried, but its manufacturer and some government regulators deny a link between cancer and glyphosate. 

In the first three months of this year, more than 539 manatees have died in Florida, an alarming rate, says Pat Rose, who directs the nonprofit Save the Manatee Club.

“This is one more serious reason for concern that long-standing human-caused exposure of fertilizers, human waste and other byproducts are endangering our aquatic ecosystems and the species that depend on them for their survival,” Rose wrote in an email.

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When they tested the sea cows’ blood, researchers found the substance, the active ingredient in Roundup and Rodeo, in the plasma of 55.8% of the creatures, and that concentrations of glyphosate in their plasma went up in the decade between 2009 and 2019.

The same level of glyphosate exposure manatees experience can cause kidney and liver damage in laboratory animals, which concerns Calusa Waterkeeper John Cassani.

The creatures’ chronic exposure in Florida waters may impact their immune and renal systems, further compounding the stress caused by other environmental factors, such as harmful algal blooms and cold weather.

“Manatees are Exhibit A that Florida’s waters are in crisis and they shouldn’t be facing this kind of pesticide threat,” said Jaclyn Lopez, Florida director of the Center for Biological Diversity in a statement. “Our beloved, chubby sea cows are dodging boat strikes, reeling from red tide and starving in the Indian River Lagoon because of water pollution. It’s heartbreaking to add chronic glyphosate exposure to the list of factors threatening manatee survival.”

Because glyphosate’s harm threshold isn’t yet clear, humans must do a better job of keeping it and other plant-killers out of waterways, Rose said – not just because they might harm the animals, but because they also deplete their food supply by causing harmful algae blooms that can shade out and kill manatees’ pastures.

“With such catastrophic losses of seagrasses it will be all the more important to protect our freshwater vegetation which can be further stressed by continued direct applications of glyphosate as well as runoff from upland applications in association with agricultural activities," Rose said.

The study was published in the journal Environment International with funding by "For Everglades Foundation and Fulbright Commission (Uruguay-U.S.) (and) the College of Veterinary Medicine of the University of Florida," the authors write in the acknowledgements.

However, some question the paper's underlying premise and some of its subsequent conclusions.

Two things in particular stand out.

More:Nearly 600 manatees died in Florida waters in 2020; draft rules could help deaths

Though the sugarcane harvest is highlighted in the study and accompanying press materials as a source of glyphosate, the study doesn't quantify how much of the  load was contributed by sugar as opposed to residential development, golf courses, row crops and other sources. Manatees also were tested in waters that aren't influenced by cane fields, including at the Florida/Georgia border and in the Crystal River in central Florida, which U.S. Sugar spokeswoman Judy Sanchez questions.

"Whoever wrote the manatee study knew next to nothing about sugarcane farming practices," she wrote in an email, "and the actual study tested manatees in the state of Georgia, Crystal River and Brevard County – nowhere near the Everglades Agricultural Area and sugarcane farming.” 

Authors Maite De María and Nancy Denslow explained in an email: "We only measured the amount that was present in the water at the locations listed in the manuscript at six times during the year with a passive sampler in the water between the first and second, the third and fourth, and the fifth and sixth sampling times. We do not know how much was contributed by each of the different sources," they wrote. "Crystal River may be a measure of what is contributed by development compared to agriculture, but we have not measured this."

The study also says that Lake Okeechobee is polluted by pesticides and fertilizer that flow into its water from farm fields to its south. “(Lake Okeechobee) receives nutrient loads and other pesticides from the Everglades Agricultural Area,” the authors write.

Except it doesn’t, says South Florida Water Management District spokesman Randy Smith.

“Water flows south from Lake Okeechobee into the Everglades Agricultural Area, then through stormwater treatment areas and into Everglades National Park," Smith said. "On the very, very rare occasion when stormwater warrants it, pumps might be turned on to provide flood prevention for residents of the communities, but it is not common practice, and it is not part of maintaining water levels on the EAA," Smith said.

To blame farming for the lake's glyphosate loads is a mistake, he said.

“I’ll go back 20 years to when I started, when the (district’s) governing board said ‘You will not use those pumps ever unless there is a threat to human safety and life in the surrounding communities due to high water levels.'”