Alligators in Georgia’s swamps are carrying worrying levels of mercury, raising concerns about the health of the wider ecosystem – and even the risks to humans, a new study has found.
Researchers from the University of Georgia and the Marine Extension and Georgia Sea Grant studied more than 100 American alligators (Alligator mississippiensis) across three locations: Okefenokee Swamp, Jekyll Island and the Yawkey Wildlife Center.
Analysing blood samples from the alligators, they discovered that mercury levels were unusually high – especially in the Okefenokee Swamp, where the toxic metal measured up to eight times higher than in the other areas.
“Mercury is a neurotoxin that is very lethal to organisms. If it builds up, it moves through the food web and creates the perfect storm. That’s what we have in the Okefenokee,” says Jeb Byers, co-author of the study, published recently in the journal Environmental Toxicology and Chemistry.
The findings raise red flags about mercury's reach through the food chain. While mercury is known to accumulate in small creatures lower down the web, the new research reveals significant build-up in a top predator – the alligator. This suggests that mercury contamination is widespread and affecting large parts of the ecosystem.
“Alligators are very ancient creatures, and we can look at them in these areas as an indicator of what else might be happening in the ecosystem,” says lead author Kristen Zemaitis. “Studying them can relate to many different things in the food web.”
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The study found that age and diet matter. Older and larger alligators had the highest levels of mercury, not only because of their longer exposure to the element but also due to eating larger, contaminated prey.
Hatchlings also showed high levels, indicating mercury can be passed from mother to offspring through the egg yolk.
Mercury often enters waterways through industrial runoff and precipitation. Once there, it can accumulate in fish and wildlife.
People who regularly eat fish or hunt game in these regions could also be at risk from mercury exposure, say the researchers, especially in areas connected to the Okefenokee, such as the Suwannee and St. Marys rivers.
The study raises questions about the sources of mercury and its full impact on the ecosystem, says Zemaitis. “Now that we know this about one of the apex predators in these systems, we wonder what else is being affected?”
Find out more about the study: Site-specific ontogenetic drivers of mercury concentrations in American alligators
Main image: Okefenokee Swamp, Georgia. Credit: Getty
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