Miami rain carries more than just droplets of water. Researchers at Florida International University (FIU) have revealed that rainwater in this region contains “forever chemicals,” or PFAS, pollutants that, as they circulate through the water cycle, contaminate areas well beyond their initial sources.
Over more than a year, the team collected 42 rainwater samples in Miami-Dade County, identifying 21 varieties of PFAS, including PFOS and PFOA, substances banned for their carcinogenic risks. Despite their ban, modern versions of these compounds persist in consumer products and appear in the rains of South Florida.
The presence of certain PFAS in the collected samples could be linked to local sources, but other substances seem to come from elsewhere. This dispersion by the atmosphere, reported in Atmospheric Pollution Researchshows that PFAS travel great distances, amplifying global pollution.
Natalia Soares Quinete, assistant professor of chemistry and lead author of the study, says air and air masses carry these contaminants to areas where they eventually affect surface water and groundwater, illustrating the extent of contamination.
These substances are designed to be extremely durable: products like food packaging, clothing or non-stick utensils are designed with PFAS that do not degrade easily. Once released into the environment, these substances accumulate, exposing humans and wildlife to risks such as liver damage, kidney damage, fertility and even certain cancers.
Quinete’s team has been tracking the presence of these pollutants in South Florida for several years. PFAS have been detected in drinking water, surface waters like Biscayne Bay, and even in local wildlife including oysters, fish and lobsters, suggesting contamination in chain ecosystems.
Rain, a logical step in their research, turns out to be an unexpected vector. The phenomenon studied by the team demonstrates that PFAS can evaporate or attach to atmospheric particles, thus circulating via air currents before being deposited on the ground by precipitation.
Between October 2021 and November 2022, PFCA compounds, common in firefighting foams and packaging, were found in 74% of samples. Their concentrations increase significantly during the dry season, when air currents from the north reach Miami, bringing PFAS produced in other regions.
Maria Guerra de Navarro, doctoral student and co-author of the study, explains that drought facilitates the dispersion of PFAS-laden particles, which are then deposited by rain. These observations provide a better understanding of the dynamics of transport of these substances.
With this new data, researchers hope to influence measures to limit the spread of PFAS. Guerra de Navarro underlines the importance of this awareness: what is emitted in one region can contaminate other territories, recalling that the prevention of this pollution is a global issue.
