Per- and polyfluoroalkyl substances (PFAS)—chemicals known for their longevity and their toxic effects—have been detected in Miami’s rainwater, a new study from Florida International University (FIU) reveals. This discovery highlights how PFAS, commonly referred to as “forever chemicals” due to their inability to break down easily, are circulating over vast distances, with significant public health and environmental implications.
Researchers at FIU spent more than a year collecting and analyzing rainwater samples from three sites in Miami-Dade County. Their findings identified 21 types of PFAS in rainwater across the city, including the now-phased-out PFOS and PFOA compounds as well as newer PFAS varieties still used in manufacturing. This research provides a disturbing insight into how these chemicals enter the water cycle, travel through the air, and are eventually deposited back into the environment, even in locations far from where they were produced.
PFAS are synthetic compounds that have become nearly inescapable, found in products from non-stick cookware and clothing to firefighting foams and cosmetics. These chemicals are designed to withstand high temperatures and resist water and grease, making them appealing to manufacturers. However, their durability also makes them difficult to break down in the environment, where they accumulate in soil, water, and living organisms. The U.S. Environmental Protection Agency (EPA) has linked PFAS exposure to a variety of serious health issues, including liver and kidney damage, reproductive harm, and cancer. Even low levels of PFAS exposure are considered hazardous, leading the EPA to set stringent limits on PFAS in drinking water supplies.
Yet, despite these known risks, PFAS continue to persist in the environment, accumulating over time and moving through air and water to locations far from their point of origin. The FIU study is one of the first to extensively document how PFAS can be carried by air masses, showing just how widespread these chemicals have become.
The FIU research team, led by Assistant Professor Natalia Soares Quinete, collected and analyzed 42 rainwater samples across Miami-Dade County between October 2021 and November 2022. Among the 21 PFAS compounds detected, several could be traced back to local sources in South Florida. However, some PFAS found in Miami’s rainwater did not match local sources, which led researchers to conclude that these chemicals are capable of traveling great distances through the atmosphere before settling into new areas.
“Our findings indicate that PFAS are practically everywhere,” Quinete stated in a press release. “Now we’re able to show the role air masses play in potentially bringing these pollutants to other places where they can impact surface water and groundwater.” The research, which has been published in Atmospheric Pollution Research, provides critical data on the transport mechanisms that make PFAS a global pollution problem, rather than one confined to specific regions.
PFAS enter the atmosphere in multiple ways, including through evaporation and by becoming absorbed into microscopic dust particles. Once airborne, these compounds are carried by shifting air currents and wind, traveling across regions and continents. When it rains, PFAS are deposited back onto the ground, into water sources, and even onto plant and animal life. This cycle of movement—evaporation, transport, and deposition—ensures that PFAS continue to circulate, contaminating new environments and impacting ecosystems as they go.
The FIU study highlights how PFAS become embedded within the water cycle, contributing to their spread across the globe. As Quinete’s team found, PFAS pollution is not limited to local areas but is part of a larger, ongoing contamination process fueled by atmospheric currents. This disturbing trend is compounded by PFAS’s resistance to breakdown, meaning they persist in the environment for decades, if not longer.
One of the study’s more surprising findings was the seasonal fluctuation in PFAS concentrations in Miami’s rainwater. During the dry season, which lasts from October through May, PFAS concentrations spiked significantly. This increase coincided with air masses traveling southward from the Northeast United States, where PFAS-producing industries are located. Maria Guerra de Navarro, an FIU graduate student who co-led the study, explained that this pattern supports the theory that PFAS from manufacturing sites in other states are transported to Miami by dry air currents.
“The seasonal variations were interesting to us,” Guerra de Navarro remarked. “We know there are northern states with manufacturing that matches back to the PFAS we saw, so it’s likely that’s where they are coming from.” The study also suggests that dry air conditions enable more PFAS-laden particles and dust to circulate, further explaining the higher concentrations observed in Miami during these months.
The implications of the FIU study extend far beyond rainwater contamination. Previous research from Quinete’s team detected PFAS in Miami’s surface waters, including Biscayne Bay, as well as in local drinking water and in marine species like oysters, fish, and lobsters. These findings indicate that Miami residents and its environment face consistent exposure to PFAS from multiple sources, raising concerns over cumulative health impacts.
As the FIU study confirms, rain is a significant pathway for PFAS reintroduction into the environment, where they can build up in water supplies, soil, and the bodies of animals and humans. This widespread contamination is especially concerning in an urban area like Miami, where the potential for human exposure is high.
While the EPA has implemented limits on certain PFAS chemicals in drinking water, the U.S. lacks comprehensive regulations to address PFAS emissions and prevent contamination in air and rainwater. The FIU team hopes that studies like theirs will provide valuable data to guide future policy and regulatory action. In light of these findings, environmental groups are calling for stricter PFAS controls to protect public health, not just in Florida but nationwide.
As PFAS contamination proves to be a borderless issue, many experts are also advocating for international cooperation in combating the spread of these chemicals. Only through concerted action on a large scale, they argue, will it be possible to reduce PFAS levels in the environment and prevent further harm.
Quinete’s team is already planning follow-up studies to measure the impact of what they call “dry deposition” of PFAS particles. Guerra de Navarro is working on quantifying PFAS concentrations in dust particles smaller than 10 microns—a particle size far smaller than a strand of human hair. This research is crucial for understanding how PFAS accumulate in the atmosphere and eventually reach rainwater, potentially informing strategies to prevent their spread.
“This is all about creating awareness that this is all one world,” Guerra de Navarro explained. “What happens in one area can impact here, there, everywhere. We have to be thinking about how to prevent these chemicals from going all over the world.”
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