Nicotine, Flavor, and More: E-Cigarette Aerosols Deliver Toxic Metals

Short abstract

In laboratory experiments, e-cigarettes generated aerosols containing nickel, lead, arsenic, manganese, and other toxic metals. None of the MODs, P ODs, or d-P ODs tested delivered completely metalfree aerosol.

E-cigarettes work by aerosolizing “e-liquids”—usually nicotine-based¹—in flavors such as tobacco, mint, and various fruits.² But users may not realize that the aerosol produced by e-cigarettes also contains mixtures of toxic metals, some of which are linked to cardiovascular disease,³ kidney disease,⁴ lung cancer,⁵ and Parkinson’s disease.⁶ New research published in Environmental Health Perspectives compares how concentrations of aerosolized metals differ among a variety of e-cigarette brands, flavors, and devices.⁷

The authors wrote that the metals they measured in e-cigarette aerosols may come not just from the e-liquid but also from the heating coil, soldered joints, and other parts of the device. Image: © iStock.com/Vershinin.

“A portion of our [measured] aerosol samples had metal levels that exceeded regulatory health standards,” says Angela Aherrera, a postdoctoral research fellow at the Johns Hopkins Bloomberg School of Public Health, and the study’s first author. Aherrera is referring to health-based exposure levels such as the US Environmental Protection Agency (EPA) air quality standards,⁸ US EPA reference concentrations,⁹ California EPA reference exposure levels,¹⁰ and the Agency for Toxic Substances and Disease Registry’s chronic minimal risk levels (MRLs).¹¹ “This is concerning given that vaping is popular among teens and young adults, some of whom have never smoked tobacco cigarettes.”

E-cigarettes, often marketed as tobacco cessation aids, first appeared on the market roughly two decades ago.¹² Some models, so-called modifiable devices (MODs), have adjustable settings, including voltage and temperature, and users can swap out heating coils and adjust battery output to alter nicotine and aerosol delivery.¹³ Other devices include cartridge- (“pod”) containing devices (PODs), of which the wildly popular JUUL was one of the first.¹⁴ These devices, whose settings cannot be adjusted, use a low-pH form of nicotine that allows for higher nicotine content and provides a smoother “throat hit.”^15,16 In 2019, manufacturers introduced disposable PODs (d-PODs) that users throw away entirely when the e-liquid cartridge is depleted.¹⁷ d-PODs are gaining in popularity, partly due to the variety of enticing flavors, appealing design, and low price.¹⁸

Aherrera and her colleagues analyzed metal concentrations from 194 e-cigarettes, including MODs, PODs, and d-PODs. Some of the devices were purchased online, and the rest were supplied by participants in the Exposure to Metals from E-Cigarettes (EMIT) Study, another ongoing study of e-cigarette metal exposure at Johns Hopkins.¹⁹ All the borrowed MODs retained the settings used by their owners in the EMIT study.

Using a machine that simulates inhalation, the team extracted aerosols that were $\mathrm{0}.25–\mathrm{0}.5\mathrm{mL}$ analyzed for 12 metals, selected for known human toxicity and likelihood of being present in aerosols (based on coil composition and previous studies): aluminum, antimony, arsenic, chromium, cobalt, copper, iron, lead, manganese, nickel, tin, and zinc. Then in a final step, the measured levels were converted into air concentrations expressed in milligrams per cubic meter for comparison with a range of health-based inhalation exposure thresholds.

According to the results, metals were measured in the aerosols produced by every device tested, and concentrations of these metals varied by orders of magnitude among the different brands, flavors, and devices. MODs generated the highest metal concentrations overall (with the exception of cobalt and nickel, which were higher in PODs and d-PODs). That is likely because MODs “allow you to increase power, temperature, and voltage, while the settings for PODs and d-PODs are fixed,” Aherrera says. Comparing flavors, tobacco POD aerosols contained aluminum, chromium, copper, iron, lead, manganese, and nickel in amounts ranging up to seven orders of magnitude higher than those in mint or mango aerosols.

Remarkably, 52% of e-cigarette aerosols exceeded the MRL for chronic exposure to nickel.¹¹ “This is especially concerning given that nickel is a known respiratory carcinogen,” says Markus Hilpert, a professor of environmental health sciences at the Columbia University Mailman School of Public Health, who was not involved in the study. In all, 14% of samples also exceeded the MRL for manganese, and other metals—including lead and arsenic—surpassed regulatory thresholds set by the US EPA⁸ and the California EPA.²⁰

Metal emissions are generated when internal components in the devices are heated. POD heating coils, for instance, are often made of nichrome, an alloy consisting of 80% nickel and 20% chromium.²¹ Other metallic components include wires, joints, and brass clamps.

Suchitra Krishnan-Sarin, a professor of psychiatry at the Yale School of Medicine, who was not involved in the study, describes the findings as significant, saying many of today’s e-cigarettes appeal strongly to young people. “The companies use youth-targeting names like Dragon’s Blood,” she says. This particular e-liquid is marketed as “an exotic blend of strong dragon fruit and raspberry flavors with the lightest touch of blood orange and a faint note of strawberry kiwi … a must try for adventurous vape users with sophisticated tastes.”²² According to Krishnan-Sarin, such a description “piques their interest in terms of what it might contain and taste like.”

Use of d-POD devices in particular has remained popular among middle- and high-school students,²³ many of whom “are developing a nicotine addiction they didn’t anticipate,” says Aherrera. Much remains unknown about how daily metal exposures that start in childhood might affect people in their later years. “This is new territory,” Hilpert says. “These exposures could potentially trigger neurological diseases, such as Parkinson’s disease. My view is that, with millions of e-cigarette users in the United States and around the world, we have a gigantic experiment going on.”