Heavy rain may be driving tire pollution into Florida waterways

Florida International University scientists have, for the first time, detected a toxic tire-derived chemical in Florida waterways and developed a new testing method that makes it easier to find and monitor the pollutant at extremely low levels. 

The study focuses on 6PPD-Quinone (6PPD-Q), a toxic chemical formed when the tire additive 6PPD reacts with ozone in the atmosphere. The compound has been linked to fish deaths in other parts of the country and is drawing increasing concern among environmental scientists. 

In the study, published in Environmental Pollution, Kassidy Troxell, research assistant professor at FIU's Institute of Environment, and collaborators from FIU, Ocean Conservancy and the University of Florida created a highly sensitive analytical method capable of detecting 6PPD-Q at concentrations that may have previously gone unnoticed. Using the new approach, researchers documented the chemical in Florida waters for the first time and found that concentrations increased following rainfall events. 

"When we have the first big rain event, we get these big pulses of stormwater into our rivers and canals," Troxell said. "This can bring higher amounts of these chemicals into our waterways." 

Researchers collected water samples from the Hillsborough River over a 10-month period and detected 6PPD-Q in every sample analyzed. The highest concentrations were consistently found near urban stormwater outfalls in downtown Tampa. 

The findings also revealed a pattern known as "first flush," in which pollutant concentrations spike after rainfall following extended dry periods. The results suggest stormwater runoff from roads and highways may be an important pathway carrying tire-derived chemicals into Florida waterways. 

While scientists have previously been able to detect 6PPD-Q, existing methods often require extensive sample preparation and analysis. The FIU team's new approach reduces manual sample handling, lowers the risk of contamination and improves consistency, making routine environmental monitoring faster and more reliable. 

Researchers compared the concentrations found in the river to an EPA freshwater screening benchmark of 11 nanograms per liter for short-term exposure in aquatic species. During some storm events, concentrations approached or slightly exceeded that benchmark. 

Separate studies in the Pacific Northwest have linked 6PPD-Q to mass die-offs of coho salmon. Scientists are now working to better understand how the chemical behaves in Florida waterways and whether repeated stormwater runoff could pose risks to local aquatic species and broader ecosystem health. 

The study was published in Environmental Pollution.