Ultrasound As Solution Against PFAS: Could Echography Rid Groundwater of Toxic ‘Forever Chemicals’?

Access to safe drinking water continues to be a major concern in our modern times. Some toxic chemicals called per- and polyfluoroalkyl substances (PFAS) can contaminate groundwater. They can persist in the environment for a long period. Hence, they are called 'forever chemicals'. A recent study shows that ultrasound technology can break down and remove these chemicals from groundwater.

Environmental Threats From PFAS

PFAS refers to a group of chemicals used to make fluoropolymer coatings and products that can resist heat, grease, oil, water, and stains. Invented nearly a century ago, these chemicals were widely used to create products such as personal care items, waterproof clothing, and cookware.

Today, experts understand that exposure to PFAS can lead to several serious health problems in humans, such as cancer and birth defects. These toxic chemicals are so common in consumer products and manufacturing that they are almost everywhere, even inside our bodies.

The bonds inside these chemicals do not break down easily, making them difficult to remove from the environment. PFAS compounds are unique because most destruction methods against hard-to-remove compounds do not work for them. Because of this, there is a need to develop various technologies to find the ones that might be useful in various applications.

Harnessing the Potential of Ultrasound

These challenges have inspired researchers at the Ohio State University to study ultrasonic degradation, a process of using sound to break down substances. As this technology could cleave apart the molecules that make up PFAS, scientists hope this approach might work against various types and concentrations of 'forever chemicals.

In this experiment, the experts created lab-made mixtures containing three differently sized compounds of fluorotelomer sulfonates, a type of PFAS compound usually found in firefighting foams. Their findings reveal that the smaller compounds were broken down in three hours, much faster than the larger ones. This result is in contrast to many other treatment approaches where it is more challenging to treat smaller PFAS. According to study co-author Linda Weavers, this mechanism makes this technology valuable.

Traditional destruction methods work by reacting PFAS with oxidizing chemicals. In contrast, ultrasound purifies these substances by emitting sound at a frequency that is lower than those used in medical imaging. The low-pitched pressure wave of ultrasound compresses and pulls the solution apart, creating pockets of vapor called cavitation bubbles.

As the bubbles collapse, they gain a lot of momentum and energy that compresses and over-compresses, heating the bubble. Just like in powerful combustion chambers, the temperature inside these bubbles can reach up to 10,000 Kelvin, which is enough to break down the carbon-fluorine bonds that makeup PFAS. In addition, it also renders the byproducts essentially harmless.

This research is still not ready to be scaled up in larger anti-contamination efforts. However, Weavers and her team hope their work can create small, high-energy water filtration devices that the public can use inside their home.