Researchers with the University of Cincinnati examined the benefit of two such tools in addressing a toxin produced by harmful algae blooms, which are becoming increasingly common in waters around the world.

Blue green algae can reproduce en masse in waters laden with nitrogen, phosphorus or other excess nutrients. These algae “blooms” also can form when water levels drop during droughts or when bottom sediments heavy with nutrients get churned up in a storm, said Minghao Kong, a doctoral graduate of UC’s College of Engineering and Applied Science.

When the blue green algae bloom and die, they release toxins into the water that can be harmful or even lethal to people and pets, Kong said.

“Boiling the water or even filtering it won’t help because that doesn’t remove the toxins, which target your liver,” he said.

Kong now studies environmental health at Emory University. He is lead author of a paper published in the journal Environmental Science & Technology examining the benefits of one particular water treatment method.

Kong said researchers have been looking at new ways to mitigate the problem after algae blooms threatened sources of public drinking water, as happened in Toledo in 2014 when the city issued a do-not-drink order to 500,000 residents. Similar incidents close beaches and lakes every year in the United States.

But the issue is of global concern, researchers said.

“Cyanotoxins are not a new phenomenon on Earth. In fact, there is speculation that dinosaurs, whose fossils were discovered near water sources in Madagascar, may have been killed by toxins produced by prehistoric harmful algal blooms,” Kong said.

Often, these algae blooms produce toxins in extremely dangerous levels measured at 100 times or higher limits than allowed by federal law. This was observed in Clear Lake, California, in 2014 and in Lake Okeechobee, Florida, in 2021, prompting advisories warning residents not to drink their water and that boiling tapwater would provide no health protection.

In the lab of the late UC Professor Dionysios Dionysiou, Kong and his co-authors examined the combination of ultraviolet light and chlorine to degrade and detoxify water laden with toxins from cyanobacteria.

Their experiments demonstrated that the combination of ultraviolet light and chlorine significantly enhanced the degradation of toxins compared to chlorine alone.

“The integration of UV radiation and chlorination offers an efficient strategy for the treatment of toxins in drinking water with both low chemical demand and energy consumption,” researchers concluded.

One concern, Kong said, is that chlorine and ultraviolet light in combination can create disinfection byproducts, including carcinogens, that are toxic to human health.

But UC's lab-scale experiments showed that UV/chlorine treatment effectively reduced the level of toxins below World Health Organization guidelines without generating harmful byproducts.

“Our tests confirmed that resulting byproduct concentrations remained within safe limits,“ Kong said.

“We found that chloride ions present in the water enhanced the process by forming reactive molecular chlorine,“ Kong explained. "Our work provides a comprehensive assessment of using UV/chlorine as a final barrier against harmful algal bloom events, especially in mitigating toxins while minimizing unintended toxic consequences.“

In the journal article, Kong and his colleagues acknowledged co-author Dionysiou, a world-renowned researcher in environmental engineering, who passed away in 2023.

“Dion was a light to all who knew him, gentle, patient and generous with his time,” researchers said in their tribute. “His life’s research in developing innovative sustainable technologies to treat water pollutants and toxins leaves our environment in a better place.”

Kong said he will be grateful always for Dionysiou’s mentorship at UC.

“I would like to sincerely thank him for providing me with numerous opportunities and his support,” Kong said. “He inspired us to continue our work on ensuring the safety of drinking water.”

The study was funded through grants from the National Science Foundation in collaboration with the Environmental Protection Agency.

Featured image at top: The late UC Professor Dionysios Dionysiou led groundbreaking efforts to improve testing and treatment of contaminated drinking water. Photo/Andrew Higley/UC Marketing + Brand

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