A study conducted on 51 types of e-cigarettes has discovered a concerning roster of chemicals. During the study, the chemicals of concern were detected in common e-cigarette flavors like the buttery compound generally found in microwave popcorn.

Scientists at the Harvard T.H. Chan School of Public Health conducted the study, published in the journal Environmental Health Perspectives. The study has considered 51 different kinds of flavored e-cigarettes and liquids from well known vendors.

The e-cigarettes were tested for the presence of 3 chemicals considered ‘high priority’in terms of respiratory risk: acetoin, diacetyl and 2,3-pentanedione.

The main concern was diacetyl because earlier study has linked inhaling the chemical to the development of a severe respiratory disorder known as bronchiolitis obliterans.

The disorder was given a nickname ‘popcorn lung’ due to a case where in a number of workers developed the health complication in 2000 after they inhaled artificial butter flavor from microwave popcorn in a processing plant.

The air inhaled by the workers had both diacetyl and acetoin. The compound 2,3-pentanedione is used as an alternate for the 2 chemicals because of its similar structure, but for inhalation it hasn’t been proved safe.

For testing the products, the researchers placed the e-cigs in a chamber, drawing air for 8 seconds at a time. Then they analyzed the vapor. At least one of the 3 chemicals was identified in 47 of the flavors.Of all, they detected measurements of diacetyl in 39 flavors, acetoin in 46 and 2,3-pentanedione in 23 flavors.

Study lead author Joseph Allen, an assistant professor of exposure assessment science at Harvard, said that the chemicals tested by them are considered safe by federal regulatory bodies when inhaled as intended. Allen said that the tested chemicals belong to a regulatory category known as ‘generally recognized as safe’ (GRAS). But, Allen has pointed out that their GRAS status was applicable for just ingestion only, not for inhalation.