Popular e-cigarette products in the United States may be contaminated with harmful bacterial and fungal toxins, a new study from Harvard researchers suggests.
When looking at 75 e-cigarette cartridges and e-liquid products from the top-selling brands in 2013, the team found that 23% contained traces of endotoxin and that that 81% contained traces of glucan.
Endotoxins are found on Gram-negative bacteria and glucan is found on most fungi. Exposure to them has been associated with health problems like asthma, reduced lung function, and inflammation, the researchers say.
"Airborne Gram-negative bacterial endotoxin and fungal-derived glucans have been shown to cause acute and chronic respiratory effects in occupational and environmental settings," David Christiani, a professor at Harvard's T.H. Chan School of Public Health and senior author of the study, said in a statement.
"Finding these toxins in e-cigarette products adds to the growing concerns about the potential for adverse respiratory effects in users."
While the team did find the contaminants present in their samples, they did not test for how much of the contaminants were in aerosols actually inhaled by users, the study says.
Brand and product names were not included in the study.
The study, published Wednesday in the peer-reviewed journal Environmental Health Perspectives, comes amid growing concern among federal health officials about potential public health effects of vaping.
The Food and Drug Administration last year declared youth vaping an "epidemic" as millions of middle school, high school and college students say they use e-cigarettes.
Earlier this month, the FDA said that at least 35 people reported seizures after using electronic cigarettes over the past decade.
The new study was funded by a grant from the National Institute for Occupational Safety and Health.
Gregory Conley, president of the advocacy group the American Vaping Association, said the study should have compared how these toxin levels in vape products would compare to cigarettes.
"With many adult smokers now mistakenly believing that vaping could be as dangerous as smoking cigarettes, it is disgraceful to release this study without an adequate comparison to cigarettes," Conley said in a statement to USA TODAY.
Conley also noted that the study looked at brands that were top-sellers in 2013, rather than more modern ones.
The research team tracked concentrations of endotoxin and glucan on 37 different types of e-cigarette cartridges and 38 e-liquid products.
Seventeen of the products had detectable concentration levels of endotoxin and 61 had detectable glucan.
Cartridges had more than three times the concentrations of glucan compared to e-liquids, regardless of brand or flavor. Glucan was also higher in tobacco- and menthol-flavored products compared to fruit flavors.
It was unknown when the contamination occurred, and the researchers said it's possible that cotton wicks could be the source because endotoxin and glucan are known contaminants of cotton fibers.
The researchers say future studies should evaluate contamination of aerosols inhaled by users, include a larger variety of products and examine the variability of these toxins within different batches or packages of the products.
Contributing: Jayne O'Donnell.
Follow USA TODAY's Ryan Miller on Twitter @RyanW_Miller.
This article originally appeared on USA TODAY: Popular vaping products contaminated with bacterial and fungal toxins, study says