Popular electronic cigarette products were contaminated with bacterial and fungal toxins linked with myriad health problems, including asthma, a Harvard said.
The study, which examined 75 popular e-cigarette products—cartridges (single use) and e-liquids (refillable material)—found that 27 per cent contained traces of endotoxin, a microbial agent found on Gram-negative bacteria, and that 81 per cent contained traces of glucan, which is found in the cell walls of most fungi.
Exposure to these microbial toxins has been associated with myriad health problems in humans, including asthma, reduced lung function, and inflammation, according to the study published in the journal Environmental Health Perspectives.
"Airborne Gram-negative bacterial endotoxin and fungal-derived glucans have been shown to cause acute and chronic respiratory effects in occupational and environmental settings," said David Christiani, a professor at Harvard T H Chan School of Public Health.
"Finding these toxins in e-cigarette products adds to the growing concerns about the potential for adverse respiratory effects in users," Christiani said in a statement.
The use of e-cigarettes has been steadily climbing in recent years, especially among high school and middle school students. It is estimated that more than three million high school students used e-cigarettes in 2018, up from 220,000 in 2011.
The research shows that chemicals linked with severe respiratory disease are found in common e-cigarette flavours.
Moreover, research has shown chronic lung impairment in populations exposed to airborne biological contaminants. Yet, according to the authors, no research exists on the potential contamination of e-cigarettes with microbes or microbial toxins.
For this study, the researchers selected 37 e-cigarette cartridges, sometimes referred to as "cigalikes," and 38 e-liquid products, which can be used to refill certain cartridges, from the 10 top-selling US brands.
The products were classified into four different flavor categories: tobacco, menthol, fruit, and other. All of the products were then screened for the presence of endotoxin and glucan.
The findings showed that 17 of 75 products (23 per cent) contained detectable concentrations of endotoxin and that 61 of 75 products (81 per cent) contained detectable concentrations of glucan.
Further analysis showed that cartridge samples had 3.2 times higher concentrations of glucan than the e-liquid samples.
Glucan concentrations were also significantly higher in tobacco- and menthol-flavored products than in fruit-flavoured products.
The study also found that endotoxin concentrations were higher in fruit-flavored products, indicating that raw materials used in the production of flavors might be a source of microbial contamination.
The researchers noted that the contamination of the products could have occurred at any point during the production of the ingredients or of the finished e-cigarette product.
They hypothesised that cotton wicks used in e-cigarette cartridges may be one potential source of contamination, as both endotoxin and glucan are known contaminants of cotton fibres.