Scientists at the University of California, Riverside have revealed that ultrasonic cigarettes, or u-cigarettes, promoted as safer alternatives to traditional e-cigarettes, could pose serious health risks due to harmful metals found in their liquids and aerosols.
Unlike conventional e-cigarettes that use heating coils, u-cigarettes employ a “sonicator” that vibrates a liquid—usually containing nicotine, flavorings, and solvents like propylene glycol or vegetable glycerin—at high ultrasonic frequencies to create microscopic aerosol droplets. This novel technology is marketed as less harmful, but evidence supporting that claim has been scarce.
The new study, published in Environmental Health Perspectives, analyzed metal and chemical content across several pod-style devices including SURGE u-cigarettes and JUUL e-cigarettes. Researchers used advanced methods such as scanning electron microscopy and inductively coupled plasma optical emission spectroscopy to detect 16 different elements in fluids and aerosols.
Esther Omaiye, the study’s lead author and a postdoctoral researcher, explained, “U-cigarettes claim to be less harmful than e-cigarettes, but there is limited scientific data to support this. We wanted to examine the chemistry and toxicology behind this new technology and understand its impact on users.”
The team found that u-cigarette fluids and aerosols generally contained higher metal concentrations than those in fourth-generation e-cigarettes. “These metals are not needed for device operation and likely come from contaminants,” Omaiye noted. “Their presence is a major health concern.”
Among the findings, silicon was detected in all tested products, while nickel appeared at low levels except in one product, the KWIT Stick, which showed alarmingly high nickel concentrations—up to 66,050 micrograms per milliliter. SURGE products contained copper and zinc in their fluids, although these metals transferred minimally to aerosols.
Senior author Prue Talbot, professor of the graduate division at UC Riverside, highlighted particularly worrying levels of arsenic and selenium in SURGE u-cigarettes. Both elements are on the FDA’s list of Harmful and Potentially Harmful Constituents. “Our results emphasize the urgent need for regulations limiting arsenic and selenium in vaping products,” Talbot said. “Regular monitoring is essential to identify products with dangerously high metal levels.”
The study raises concerns about long-term health effects linked to u-cigarette use, including risks of cancer and neurotoxicity. Inhalation of metals like arsenic and nickel can cause lung diseases, organ damage, and cancer. Even metals essential in small amounts, such as zinc and selenium, become toxic at high concentrations, especially when inhaled as fine aerosols that penetrate deep into lung tissue.
Omaiye urged caution for current and potential users: “Users must be aware of what their devices contain and critically evaluate safety claims. Non-vapers should avoid starting, but if they choose to vape, understanding these risks is crucial.”
Looking ahead, the researchers plan to expand their investigations into emerging tobacco products and their public health impact. Talbot stressed, “Inhalation exposure to metals like arsenic, nickel, lead, or chromium is hazardous even at low doses over time, as the lungs cannot filter these toxins as the digestive system does.”
Omaiye called for independent research and stricter manufacturing controls to ensure safer vaping devices and liquids. “Medical professionals, regulators, and consumers must stay vigilant as vaping technologies evolve, recognizing that changes in device design do not automatically eliminate health risks.”
This research was funded by the National Institutes of Health, California’s Tobacco-Related Disease Research Program, and UC Riverside. Omaiye also received a UC President’s Dissertation Year Fellowship.
The full study is titled “Quantification of 16 Metals in Fluids and Aerosols from Ultrasonic Pod-Style Cigarettes and Comparison to Electronic Cigarettes.”
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