Destroying toxic “chemicals forever” can be found in foods in your pantry.
Perfluoroalkyl and polyfluoroalkyl substances, also known as PFAS, can persist in the environment for centuries. Although health effects of only a fraction of thousands of different types of PFAS have been studied, studies link the high levels of some of these common man-made chemicals to health problems such as cancer and reproductive problems.
Now research shows that the combination with ultraviolet and a couple of common chemicals can break down almost all PFAS in concentrated solution in just a few hours. The process involves exposure to UV radiation in a solution containing PFAS and iodide, which is often added to table salt, and sulfite, a common food preservative, researchers said on March 15. Environmental Science and Technology.
“They show that when [iodide and sulfite] combined, the system is becoming much more efficient, ”said Gareth McKay, an environmental chemist at Texas A&M University at College Station who was not involved in the study. “It’s a big step forward.”
The PFAS molecule contains a chain of carbon atoms that are bound to fluorine atoms. The carbon-fluorine bond is one of the strongest known chemical bonds. This sticky connection makes PFAS useful for many applications such as water- and oil-repellent coatingsfire foam and cosmetics (CH: 04.06.19; CH: 15.06.21). Due to their widespread use and durability, PFAS have been found in soil, food and even drinking water. U.S. Environmental Protection Agency sets healthy reference levels for PFOA and PFOS – two common types of PFAS – at 70 parts per trillion.
Wastewater treatment plants can filter PFAS from water using technologies such as activated carbon filters or ion exchange resins. But these removal processes are concentrating PFAS in waste that requires a lot of energy and resources to destroy, says study co-author Gignon Liu, a chemist-ecologist at the University of California, Riverside. “If we don’t [destroy this waste]there will be problems of secondary pollution ”.
One of the most well-studied methods of PFAS degradation involves mixing them in a solution with sulfite and then treating the mixture with UV rays. The radiation detaches the electrons from the sulfite, which then move around, breaking the stable carbon-fluorine bonds and thereby destroying the molecules.
But some PFAS, such as a type known as PFBS, have proven to be difficult to degrade in this way. Liu and his colleagues irradiated a solution containing PFBS and sulfite throughout the day, only to find that less than half of the contaminants in the solution disintegrated. Achieving higher levels of degradation required more time and additional infusion of sulfite at regular intervals.
The researchers knew that iodide under the influence of UV radiation produces more electrons that cut bonds than sulfite. And previous studies have shown that UV radiation is combined with iodide alone can be used to degrade PFAS chemicals.
Thus, Liu and his colleagues exploded with UV rays on a solution containing PFBS, iodide and sulfite. To the researchers ’surprise, less than 1 percent of persistent PFBS remained after 24 hours of irradiation.
Moreover, the researchers showed that this process destroyed other types of PFAS with similar efficiencies, and was also effective when PFAS concentrations were 10 times greater than only UV light and sulfite could degrade. And by adding iodide, the researchers found that they can speed up the reaction, Liu says, making the process much more energy efficient.
The iodide and sulfite solutions worked together to support the breakdown of PFAS molecules, Liu explains. When ultraviolet rays release an electron from iodide, this iodide is converted into a reaction molecule, which can then re-capture the released electrons. But here sulfite can enter and bind to these reactive molecules and to the oxygen that absorbs electrons in solution. This sulfite “trap” allows you to keep the released electrons free to cut PFAS molecules for eight times longer than if there was no sulfite, the researchers said.
Surprisingly, no one has previously demonstrated the effectiveness of using iodide sulfite to degrade PFAS, McKay says.
Liu and his colleagues are now collaborating with the engineering company, using their new process to process PFAS into a concentrated waste stream. The pilot test will be completed in about two years.