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Microplastics alter the fate of inland-derived microbial contaminants transported into coastal environments by tropical cyclones
Summary
When hurricanes like Milton wash bacteria from land into coastal waters, tiny plastic particles act like rafts that these germs cling to—letting them survive twice as long and stick around for weeks or months instead of quickly dying off. This matters because some of these bacteria carry antibiotic-resistant genes, and microplastics may help them linger in swimming waters and potentially share that resistance with local marine bacteria, meaning our current water safety tests might be underestimating how long risks last after big storms.
Tropical cyclones transport diverse contaminants, including microbial contaminants and microplastics, from inland to coastal environments. However, the fate of these inland-derived contaminants after transport remains poorly understood. Here, we investigated the mechanisms by which microplastics affect the fate of inland-derived microbial contaminants in coastal waters. Field observations following Hurricane Milton revealed substantial transport of microplastics from inland areas to Florida’s Gulf Coast, where antimicrobial resistance genes (ARGs) associated with particles larger than 25 µm accounted for approximately 25% of the total ARG abundance introduced during the hurricane event. We confirmed that biofilm formation on microplastics reduced the decay rates of inland-derived bacteria to about half under simulated coastal conditions. We also confirmed that inland-derived bacteria coexisted with indigenous marine bacteria in coastal environments, facilitated by microplastics, for extended periods (weeks to months), posing a potential risk of horizontal gene transfer of ARGs from inland to coastal environments. Consequently, microplastics may extend the impact of storm-introduced microbial threats beyond what is captured by conventional fecal indicator bacteria-based assessments. This study highlights the need to reconsider microbial water quality recovery in coastal environments by accounting for particle-associated processes following extreme events.