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Hopkins' Researchers Discover Carcinogenic Metals in E-Cigarette Liquid


Analysis of the liquid used to make the aerosol in e-cigarettes has led to the discovery of high levels of 5 potentially toxic heavy metals.

Analysis of the liquid used to make the aerosol in e-cigarettes has led to the discovery of high levels of 5 potentially toxic heavy metals. The study, conducted by researchers at the Johns Hopkins Bloomberg School of Public Health, adds to the growing concern around the safety of e-cigarettes.

Five leading brands of first-generation e-cigarettes, 3 of which made up 71% of the total market share in the United States in 2015, were included in the study. The liquid in the e-cigarette was then extracted prior to it being heated by the metal coil, and the concentration of 5 metals–cadmium, chromium, lead, manganese, and nickel–was tested. Only 1 flavor was tested across brands for the sake of consistency.

All 5 metals were present in all the brands, but their concentration varied, cadmium being the lowest. The brand that had the highest concentration of all 5 metals had nickel levels at 22,600 µg/L, 400 times the brand with the lowest concentration of nickel. The concentration of manganese in the same brand was 690 µg/L, 240 times the concentration of another brand. Nickel is a group 1 carcinogen that is known to cause bronchitis and lung cancer. E-cigarettes containing nickel have also been shown to be responsible for contact dermatitis in the oral cavity. Lead is known to be toxic even at low concentrations and inhaled manganese is a potent neurotoxin.

“We do not know if these levels are dangerous, but their presence is troubling and could mean that the metals end up in the aerosol that e-cigarette users inhale," lead author Ana María Rule, PhD, MHS, assistant scientist in the Department of Environmental Health and Engineering at Bloomberg, said in a statement. "One of the things that is troubling is that the metals in e-cigarette coils, which heat the liquid that creates the aerosol, are toxic when inhaled, so perhaps regulators might want to look into an alternative material for e-cigarette heating coils.”

The authors conclude that the variability in the levels of the metals across brands makes it difficult to identify a brand that may be less harmful for consumers, but recommend changing the metal used to make the heating coil, which in most cases is nichrome.

The FDA on its part has enforced tighter regulations on e-cigarette manufacturers. Last year, the regulatory body banned the sale of e-cigarettes to those younger than 18 years. The FDA also forced manufacturers to provide product details, including ingredients, manufacturing processes, and scientific data.


Hess CA, Olmedo P, Navas-Acien A, Goessler W, Cohen JE, Rule AM. E-cigarettes as a source of toxic and potentially carcinogenic metals. Environ Res. 2017;152:221-225. doi: 10.1016/j.envres.2016.09.026.


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