Tracking Down the Hidden Pollutants That Make Wildlife Sick
- Lela Nargi, Knowable Magazine
- 7 hours ago
- 7 min read
A new technique for detecting unknown and unlooked-for chemicals is revealing dozens of contaminants in alligators, sea lions, and condors.
This article originally appeared in Knowable Magazine, a nonprofit publication dedicated to making scientific knowledge accessible to all. Read the original article here and sign up for Knowable Magazine’s newsletter.
Something was wrong with the alligators.
Off and on for five years, a team of scientists had fished for the powerful reptiles in four spots in the 9,000-square-mile Cape Fear River Basin in North Carolina — a meandering, tentacled watershed that provides drinking water to more than a tenth of the state’s residents.
The team reeled in dozens of the thrashing animals on hooked lines, pulling them to shore and securing their powerful jaws with duct tape. Even before running diagnostics, the researchers could see that some of the creatures were sick, covered in festering wounds. That wasn’t normal, says Erin Baker, an analytical chemist at the University of North Carolina: Crocodilians’ strong immune systems generally protect them from infections.
Alligators are sentinel species — animals whose failing health or behavior indicates environmental contaminants that might also be a danger to people. Since some chemicals become increasingly concentrated in animal tissues as they move up the food chain, long-lived, top predators like alligators — which may spend 50 years or more swimming and eating fish in potentially polluted water — are exemplary sentinels of lurking health threats. “They can give us a really interesting, localized perspective on what they’re being exposed to,” says Anna Boatman, a former Ph.D. student in Baker’s lab.
Researchers have long used a technique called targeted analysis to screen for predetermined lists of chemicals. But that is a narrow approach. Though it can detect minute concentrations of substances, it’s useful when “you already know what to look for,” says Eunha Hoh, an environmental and health scientist at San Diego State University.
In recent years, improvements to an emerging technique, called non-targeted analysis, have allowed scientists like Hoh and Boatman to cast a wider net. By running samples such as blood plasma or fat through a mass spectrometer, they can look for chemicals that elude more conventional methods, Boatman says. The trade-off? “We can’t necessarily say what those chemicals are,” she says, or their exact concentration.
Scientists are using non-targeted analysis to detect wide swaths of whatever chemicals are lingering out there, ones that government agencies like the US Environmental Protection Agency aren’t looking for or don’t even know about. Without it, regulators and researchers risk “missing important contaminants because they were not on your starting list,” says Sara Nason, a chemist with the Connecticut Agricultural Experiment Station and chair of the Best Practices for Non-Targeted Analysis working group.
A toxic legacy
Researchers have known for at least a decade that Cape Fear gators are steeping in a brew of per- and polyfluoroalkyl substances (PFAS), a class of more than 14,000 chemicals found in plastics, firefighting gear, and nonstick coatings. The Chemours Company plant, which sits along the Cape Fear River in Fayetteville, has manufactured these chemicals there for almost 50 years. Though the plant stopped discharging contaminated processing water into the watershed in 2017, testing by various groups shows that PFAS remain present downriver.
To better understand the impact on alligators, Boatman and Baker devised a study to identify as many PFAS compounds in the creatures’ blood as possible. “Up to this point, there’s only been a handful of them that are commonly measured,” Boatman says. She used non-targeted analysis to screen the plasma of 167 alligators caught in Cape Fear, in a lake just outside the basin, and in a river in Florida, where — as far as researchers know — no PFAS manufacturing has ever happened. Boatman discovered 46 distinct PFAS compounds in the gator blood, two of them new to science.
The wound-prone Cape Fear gators, who live closest to the Chemours plant at around 90 miles downriver, showed the most kinds and highest concentrations of PFAS. In an earlier study, researchers at North Carolina State University had correlated those high concentrations with raised activity of a gene connected to disrupted immune function. Basically, says Baker, in those Cape Fear gators, “Their immune system isn’t working as well.”
All the gators — even those from the Florida river with no PFAS manufacturing — contained some of the toxic chemicals in their blood. Although Boatman and Baker can’t say for sure how the chemicals traveled so far from their original source, possibilities include illegal dumping, runoff leaching from landfills, and volatilization — when chemicals become airborne as gases then rain back to Earth somewhere else. Once the chemicals enter surface waters, they’re taken up by plankton and fish. These, in turn, are gobbled by bigger animals, moving up the food chain to the apex predators, whose blood and other tissues accumulate and hold onto the compounds.
From gators to sea lions
In her lab northeast of San Diego Bay, Hoh uses non-targeted analysis to examine tissue from sea lions, dolphins, and other marine animals. She’s hunting for chemicals containing halogens, elements that form highly stable bonds with carbon atoms and can persist for decades. Halogen-based chemicals include PFAS, the potent herbicide DDT, and PCBs, a group of carcinogenic industrial chemicals that were banned in 1979.
Some of Hoh’s research focuses on sea lions in the Southern California Bight, a 430-mile curve of coast that stretches from Point Conception near Santa Barbara to just past San Diego in Baja California. The bight has been notorious since the 1960s for having high levels of DDT contamination, thanks to wastewater discharge and dumping by DDT manufacturer Montrose Chemical Company.
For 40 years, sick and dead sea lions have frequently become stranded along the bight, many afflicted with virus-triggered reproductive cancers similar to human papillomavirus-caused cervical cancers in people. In the early 2010s, previously undiscovered containers filled with DDT and DDT byproducts were found leaking into the bight in the waters off Santa Catalina Island. Veterinarian and researcher Alissa Deming of the Pacific Marine Mammal Center in Laguna Beach, California, a frequent collaborator of Hoh, later showed that the sea lion cancers were linked to increased DDT levels.
By using non-targeted analysis on stranded sea lions’ blubber that the National Oceanic and Atmospheric Administration had stashed in its freezers, Hoh identified 194 halogen-based compounds — including DDT — in marine mammals in the bight; she also found several hundred compounds (including 45 DDT-related) in the blubber of dolphins. Non-targeted analysis, Deming says, “is really opening up doors we previously hadn’t been able to look through.”
Condors on the edge
Beyond detecting persistent environmental contaminants, the technique can guide wildlife management. Endangered California condors are one notable beneficiary. These scavengers were nearly extinct by the 1960s, due in part to DDT exposure that can thin the shells of incubating eggs. But the birds are making a comeback — about 370 California condors now soar in the wild — thanks to a workaround devised by conservationists to hatch eggs and raise chicks in captivity. Still, their recovery has faced numerous challenges, such as lead poisoning from spent ammunition.
Another important clue to their struggles is their food source, according to Christopher Tubbs, a reproductive scientist at the San Diego Zoo Wildlife Alliance. Condors living on the coast frequently eat stranded sea creatures, and at first, that was considered a good thing. “The idea was, wow, they’ll have all these marine animals to eat, a free but also nutritionally rich food source,” Tubbs says. But mounting evidence, including the discovery of the leaking DDT, raised alarms that condors were eating contaminated blubber.
Scientists had previously found that coastal condors had a greater probability of hatching failure. So Tubbs asked Hoh to test plasma from coastal condors and compare it to plasma from inland condors that did not have access to ocean mammal meals. Hoh found that coastal condors had seven times more DDT and DDT-related chemicals pumping through their systems — a plausible cause of hatching failures for birds on California’s Big Sur coast.
As a conservationist, Tubbs has experience responding to these kinds of threats. For example, in 2016, he discovered that the food for southern white rhinos at the zoo contained endocrine-disrupting phytoestrogens that caused declines in fertility. Once the zoo switched the feed, several new calves were born to previously unsuccessful rhino moms.
For condors, Tubbs has a different sort of intervention in mind. New generations of captive-raised condors are released annually; he believes that Baja California could be a less dangerous habitat for them. Chemical concentrations in stranded animals are lower there, Hoh has found, and probably won’t interfere with condor endocrine systems and reproduction. “Now we have a potentially new suitable habitat to encourage them to go to and explore,” says Tubbs.
But other researchers don’t have a similar recourse — there’s no way to move gators, dolphins, and pinnipeds into cleaner waters. As federal agencies under the Trump administration roll back air, water, and health protections for species, it’s hard not to feel bleak about helping these animals, researchers say. “It is not the time to be pulling back regulations, because they’re already fighting so hard,” Deming says.
Still, small steps toward a healthier future for all animals — including humans — remain possible. New findings indicate that DDT tends to concentrate within the top 10 centimeters of sediment in bodies of water. And so Deming thinks it would help to convince fisheries to dredge up less of it by avoiding trawling in contaminated areas. Anyway, “Who wants to eat fish from a DDT dump zone?” she says.
The flood of new data coming out of non-targeted analysis studies is clarifying that more potentially toxic chemicals are circulating than we’ve been aware of. “It can feel quite overwhelming,” Boatman says. “But I do think that slowly chipping away and learning, one chemical at a time, is better than nothing.”
