(CBS Local) — A new study is raising concerns about e-cigarettes after several toxic metals were found in the vapors users inhale.

According to a Feb. 21 report in Environmental Health Perspectives, a large number of devices were producing “unsafe levels of lead, chromium, manganese and/or nickel.” Researchers at Johns Hopkins Bloomberg School of Public Health studied the e-cigarettes of 56 individuals and nearly half of them produced aerosol samples containing dangerous levels of lead in them.

“The actual levels of these metals varied greatly from sample to sample, and often were much higher than safe limits,” senior author Ana María Rule said in a press release.

The Johns Hopkins team tested both the liquid in the e-cigarette dispensers and the aerosol users inhale into their lungs for 15 common metals. Scientists found that while the liquids contained small traces of the metals, the aerosol became toxic once the liquid was heated by a battery-powered metal coil.

Although not being part of an e-cigarette coil, the scientists found that the dangerous chemical arsenic was also being produced by the heating process. “We don’t know yet whether metals are chemically leaching from the coil or vaporizing when it’s heated,” Dr. Rule added.

The reports warns that constant inhalation of these metals has been linked to lung, liver, and brain damage, as well as various forms of cancer. A previous study has also claimed that vaping was doing as much damage to a user’s DNA as unfiltered tobacco cigarettes.