They added bromide to the mixture and, indeed, the cyanobacteria produced a toxin. Niedermeyer
I was finally able to call Wilde and tell him they found the killer. “It was awesome,” he says.
Robert Sargent, program director for the Georgia Department of Natural Resources, describes the discovery as “exceptional news.” He’s especially excited that the researchers found a way to detect the toxin in the lab. “It’s just remarkable for the ecology, to allow us to better understand this process and maybe control it,” he says. He points out that while eagle deaths are alarming, they are a sign of a much bigger problem. “Anytime we see disease or death of species at the top of the food chain, it’s a red flag for the potential health of the environment,” he says.
After finding the toxin, the research team picked up speed. They isolated the bromide-containing compound and confirmed that it was present in dead birds that showed lesions. They examined the hydrilla plant itself and found that it was able to enrich bromide in the environment, making it even more available to cyanobacteria. “The concentration of bromide in the plant is much higher than in water or in the sediment where the plant grows,” explains Niedermeyer. “It’s quite intriguing, but we don’t know why the factory is doing it.”
But in this murder mystery, identifying the culprit isn’t quite the same as ending the story. The team still have a lot of questions. Did cyanobacteria invade the hydrilla or was it already in the water? Is bromide naturally occurring or could it come from man-made sources such as coal-fired power plants and flame retardants? Hydrilla is such a persistent pest that people have tried using herbicides like diquat dibromide to kill it; could this herbicide be the source of the ingredient that creates this toxin? Wilde and Niedermeyer think it’s possible.
They are also very concerned whether this neurotoxin could affect humans who eat infected poultry. “It could be a real problem, but we don’t know it yet,” says Niedermeyer. Wilde wants to start surveillance in more places. Not all lakes that have hydrils have had an outbreak of AVM, but there are many where the weed has been treated with herbicide, and they could potentially become toxic in the future. Wilde hopes that with more surveillance, scientists can anticipate possible outbreaks and prevent it from spreading further.
Sargent adds that residents can also play a role in efforts to control AVM outbreaks by not dumping aquarium plants in waterways. Boaters can remove aquatic plants from their propellers and hulls, and if people see waterfowl or birds of prey behaving strangely, they can report those sightings to their national wildlife agency.
The only management of epidemics that have already occurred has proved difficult. Hydrilla is a stubborn plant. The Army Corps of Engineers was lucky using herbivorous carp to gnaw the grass, but even after being nibbled by fish, it will grow back from tubers buried in the sediment of the lake. And even if it grows slowly, Aetokthonos hydricolla is just as difficult to eliminate. “They just survive. You can’t kill them, ”says Niedermeyer. He remembers a few cultures in dishes in his lab that had been overlooked and were not being properly maintained. “We were like, ‘OK, it’s dead,’” he said. “But no. If you add just a little fresh medium, it will start to grow again.”
Niedermeyer says that now that they know what they’re looking for, scientists have a better chance of stopping the killer once and for all. “Now that we are aware of the problem, we can test for cyanobacteria. We can monitor the toxin. We can start sampling the water bodies for bromide, ”he says. “Now that we know what we’re looking for, we can start to find a solution.”
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