Overall, the secondhand smoke generated by electronic cigarettes is less toxic that that from traditional cigarettes, but still releases chemicals into the air that are a health concern, says new research out of USC.

The findings of the new work have been published online by the Journal of Environmental Science, Processes and Impacts.

Scientists from the University of Southern California acknowledge secondhand smoke from e-cigarettes represent a dramatic decrease in exposure to harmful particles, including close-to-zero exposure to organic carcinogens.

While the smoke from tobacco contains high levels of polycyclic aromatic hydrocarbons, or carcinogenic organic compounds, e-cigarettes generate virtually none of those toxins, since they don't burn organic material the way trtaditional cigarettes do.

But, it was also found e-cigarette emissions contain certain harmful metals -- such as the element chromium -- at notably higher rates.

Nickel, as well, is produced by e-cigarettes at levels four times higher than normal cigarettes.

The USC research also found lead and zinc in second-hand e-cigarette smoke, though concentrations of those metals were lower than in normal cigarettes.

"Our results demonstrate that overall electronic cigarettes seem to be less harmful than regular cigarettes, but their elevated content of toxic metals such as nickel and chromium do raise concerns," Constantinos Sioutas, a professor at the USC Viterbi School of Engineering and a corresponding author of the research, said in a university news release.

Sioutas and his colleagues at the Fondazione IRCCS National Institute of Cancer Research in Milan, Italy, set out to quantify the level of exposure to harmful organics and metals in second-hand e-cigarette smoke, with the expectation of offering greater insight for regulatory authorities.

"Studies of this kind are necessary for implementing effective regulatory measures. E-cigarettes are so new, there just isn't much research available on them yet," said Arian Saffari, a a doctoral student at USC Viterbi and the lead author of the paper. "The metal particles likely come from the cartridge of the e-cigarette devices themselves -- which opens up the possibility that better manufacturing standards for the devices could reduce the quantity of metals in the smoke."

All of the experiments for the study were conducted in offices and rooms; while volunteer subjects smoked both regular and electronic cigarettes, researchers collected particles in the indoor air and studied the chemical content and sources of the samples.

"Offices and rooms -- not laboratories -- are the environments where you're likely to be exposed to second-hand e-cigarette smoke, so we did our testing there to better simulate real-life exposure conditions," Saffari explained.

The study compared the smoke from a common traditional cigarette brand with smoke from one of the most popular brands of e-cigarettes on the an European market, an Elips Serie C.

The researchers noted the results from their experiments could turn out differently, based on which types of cigarettes and e-cigarettes are tested.