 "e-cigarettes")
E-cigarettes - often touted as a safer alternative to smoking tobacco - may expose vapers to toxic metals such as lead, a study warns.
The study, published in the journal Environmental Health Perspectives, examined e-cigarette devices owned by a sample of 56 users.
Researchers from Johns Hopkins University in the US found that significant numbers of the devices generated aerosols with potentially unsafe levels of lead, chromium, manganese and/or nickel.
Chronic inhalation of these metals has been linked to lung, liver, immune, cardiovascular and brain damage, and even cancers.
"It's important for the e-cigarette companies and vapers themselves to know that these heating coils, as currently made, seem to be leaking toxic metals - which then get into the aerosols that vapers inhale," said Ana Maria Rule, assistant scientist at Johns Hopkins University.
E-cigarettes typically use a battery-supplied electric current that passes through a metal coil to heat nicotine-containing "e-liquids," creating an aerosol - a mix including vaporised e-liquid and tiny liquid droplets.
Vaping, the practice of inhaling this aerosol as if it were cigarette smoke, is now popular especially among teens, young adults and former smokers.
A 2017 survey of 8th-, 10th- and 12th-grade students in public and private schools, sponsored by the National Institute on Drug Abuse, found that about one in six had used e-cigarettes in the previous 30 days.
Vaping is popular in part because it provides the nicotine "hit" and the look and feel of tobacco-smoking but without smoking's extreme health risks.
Evidence that vaping is not entirely safe continues to accumulate, however. Recent studies have found that e-cigarette liquids contain flavourings and other chemicals that harm cells in standard toxicology tests.
Other studies, including one last year from Rule's group, have detected significant levels of toxic metals in e-liquids exposed to the e-cigarette heating coil.
Researchers recruited 56 daily e-cigarette users from vaping conventions and e-cigarette shops around Baltimore during the fall of 2015.
Working with participants' devices, the scientists tested for the presence of 15 metals in the e-liquids in the vapers' refilling dispensers, the e-liquids in their coil-containing e-cigarette tanks and in the generated aerosols.
They found minimal amounts of metals in the e-liquids within refilling dispensers, but much larger amounts of some metals in the e-liquids that had been exposed to the heating coils within e-cigarette tanks.
The difference indicated that the metals almost certainly had come from the coils. Scientists showed that the metal contamination carried over to the aerosols produced by heating the e-liquids.
Of the metals significantly present in the aerosols, lead, chromium, nickel and manganese were the ones of most concern, as all are toxic when inhaled.
E-cigarette heating coils typically are made of nickel, chromium and a few other elements, making them the most obvious sources of metal contamination, although the source of the lead remains a mystery.
"We don't know yet whether metals are chemically leaching from the coil or vaporising when it's heated," Rule said.
