Ultrasound is a powerful tool with diverse applications in medical diagnostics (diagnostic sonography), therapeutics (treatment of soft tissue ailments), industry (cleaning, welding, cutting, shaping, separating, mixing, etc.), and agriculture. Airborne power ultrasound is a green technology with significant potential for food and environmental applications. For example, the exposure of soybean seeds to the airborne ultrasound increased water uptake without altering the morphology and the wettability of the seed coat; the implication of ultrasound increased the yield rate constant for the ultrasound extraction of saponins from alfalfa leaves almost two times more than that of routine heat-reflux methods; and ultrasound has been widely used to reduce the energy consumption and drying time of herbs.
A recent study by the Department of Plant Biology at Tarbiat Modares University in Iran was conducted to elucidate the physiological responses of plant cells to airborne ultrasound in tobacco plants. Homogeneous suspension-cultured tobacco cells were subjected to airborne ultrasound at 24 kHz in two pulsatile and continuous modes for 10 and 20 seconds. The study’s outcome revealed that airborne ultrasound triggered the production of H2O2, elevated internal calcium concentration, and reduced antioxidant capacity upon cavitation. Alteration of covalently bound peroxidase and other wall-modifying enzyme activities was accompanied by reduced cellulose, pectin, and hemicellulose B but increased lignin and hemicellulose A. The biomass and viability of tobacco cells were also significantly decreased by airborne ultrasound, which ultimately resulted in programmed cell death and secondary necrosis. The results highlight the potential risks of even short-time exposure to the airborne ultrasound on plant physiology and cell wall chemical composition raising significant concerns about its implications.
In conclusion, even short exposures to ultrasound can be damaging to tobacco plants, meaning growers should evaluate sound pollution effects on the plant’s living status. Various machines act as sources of airborne ultrasound, including high-frequency cutting tools, ultrasonic cleaners, welding equipment, and some laboratory and medical instruments such as fans, compressors, air handling units, transformers, high-voltage power lines, and electrical discharge machining.