As another heavy sargassum season unfolds, many beachgoers are asking the same question: Is it safe to be near it?
A recent University of Miami study offers an evidence-based answer, particularly for children. Overall risks are low, but not zero. The research, published in Exposure and Health, found that noncancer risks from arsenic exposure during beach play are minimal. But it also identified small increased cancer risks in certain scenarios, particularly from skin contact and accidental ingestion, underscoring the need to better understand how children interact with sargassum on the beach.
That study is part of a growing body of work from researchers at the University's College of Engineering. Environmental engineering professor Helena Solo-Gabriele and mechanical engineering assistant professor Jiayu Li are studying what happens when massive amounts of seaweed wash ashore and begin to break down.
Sargassum naturally accumulates arsenic, and when it washes up on beaches, that contaminant does not stay contained. In a study simulating real beach conditions, the research team found that arsenic can move into surrounding environments, seeping into water, transferring into sand, and even entering the air as the seaweed decomposes.
"The risks are associated with long-term, repeated, and prolonged exposures, especially for children with a condition called pica, which is a tendency to intentionally consume nonfood items," said Solo-Gabriele. "Encouraging basic hygiene can help reduce exposure, such as washing hands before eating at the beach. Taking a shower after returning home would also help reduce exposure."
The way sargassum is handled on shore can also affect where that arsenic ends up. When sargassum is mixed into sand rather than removed, arsenic levels in the sand were found to be higher, pointing to how crucial mitigation efforts are.
As seaweed rots, it also releases gases that affect air quality. Lab studies show that emissions of sulfur-containing gases, mainly hydrogen sulfide (H2S), spike within the first couple of days of decomposition. The findings highlight why large, soaked accumulations of sargassum can quickly become a public health concern.
"The smell is only part of the story," says Li. "As sargassum decomposes, it can release hydrogen sulfide and other sulfur-containing gases, and these emissions may be a concern when sargassum accumulates in large piles. If beachgoers notice a strong rotten-egg odor or feel eye, throat, or breathing irritation, that is a good sign to move away from the area."
Taken together, the research paints a nuanced picture. Sargassum is not just a visual or economic problem. It is a dynamic environmental system that releases gases, concentrates contaminants, and shifts those contaminants across air, water, and sand as it decomposes on shore.
"Sargassum is an important part of ocean and coastal ecosystems," said Solo-Gabriele. "Practicing good hygiene and discouraging its consumption can help reduce the already low risks associated with it."
