New research reveals that sulfur runoff from sugarcane farming is amplifying toxic mercury levels in Florida’s wetlands—posing a preventable threat to wildlife and human health.
Key Points at a Glance
- Sulfur used in sugarcane cultivation is converting mercury into neurotoxic methylmercury in the Florida Everglades.
- Methylmercury levels in fish can reach up to 10 million times the concentration in surrounding waters.
- Mercury enters the ecosystem via rainfall, but sulfur accelerates its transformation into toxic form.
- Reducing sulfur use could lead to a rapid decline in mercury contamination in fish.
- Researchers call for local agricultural and sustainability reforms to mitigate the crisis.
In the vast wetlands of the Florida Everglades, a hidden chemical chain reaction is threatening one of the world’s most biologically rich ecosystems—and the health of people who depend on it. According to a new study from the University of California, Davis, sulfur applied to nearby sugarcane fields is fueling the conversion of mercury into a far more toxic form known as methylmercury, which accumulates in fish and magnifies through the food chain.
The research, published in Nature Communications, focuses on water systems upstream of Everglades National Park, where sulfur runoff from agricultural canals seeps into the wetlands. Although mercury pollution has long been a concern in Florida, this study provides a critical missing link: how added sulfur stimulates anaerobic bacteria and archaea to convert atmospheric mercury—deposited via near-daily rainfall—into a potent neurotoxin.
“Methylmercury is uniquely dangerous because it crosses the blood-brain barrier and the placenta, making it a threat to both adult cognition and early development,” explained lead author Brett Poulin, an environmental toxicologist at UC Davis. “What’s alarming is how directly sulfur applications influence this transformation—and how quickly the problem might be reversed with better land management.”
By collecting water samples and mosquito fish across canal-fed wetlands, Poulin and his colleagues documented methylmercury concentrations in fish that were as much as 10 million times higher than the levels in the water they inhabited. The implications are disturbing: people who rely on local fish for food and top predators like birds and alligators are being exposed to some of the highest methylmercury levels recorded anywhere in the world.
While mercury contamination is a global problem—prompting the United Nations to adopt the Minamata Convention in 2013—solutions have often felt slow and distant. But here, the source of amplification is local and potentially addressable. Sulfur is not regulated in agriculture the way nitrogen or phosphorus is, despite its now-documented role in intensifying mercury toxicity.
“This study offers a rare opportunity,” said Poulin. “We know the causal pathway, and we can change it. Reducing sulfur inputs from agriculture would decrease methylmercury levels rapidly.”
The Everglades restoration is a $26 billion effort to preserve a unique ecosystem and its water quality. But more than 60% of the region has been affected by sulfur contamination. Addressing this chemical legacy could not only protect biodiversity, but also reduce health risks in surrounding communities.
With support from the U.S. Geological Survey’s Greater Everglades Priority Ecosystems Science Program, Poulin’s team—including scientists from USGS and other institutions—used a multidisciplinary approach to trace the connection between land-use practices and toxic exposure in fish. Their conclusion: agricultural management and sustainability plans should now prioritize sulfur reduction, particularly in crops like sugarcane that require pH adjustment in alkaline soils.
The potential for change is striking. “We’re not talking about waiting decades,” Poulin emphasized. “This is a case where targeted, local action could yield results very quickly.”
As the Everglades battles invasive species, sea-level rise, and climate stress, the last thing it needs is a preventable chemical cascade. This study offers both a wake-up call and a roadmap: by addressing how we farm, we may yet protect how we live.
Source: University of California – Davis
