New research from Johns Hopkins Bloomberg School of Public Health has found that a number of e-cigarette vapors contain unsafe levels of toxic metals, including lead and chromium. It is suspected that blame lies with e-cigarette heating coils that are contaminating the aerosols generated by the device.

The study recruited 56 e-cigarette users and examined each participant's own device for the presence of 15 different metals. Minimal amounts of the metals were identified in the e-liquids, but their volumes significantly increased after the liquids were exposed to a device's heating coils. And those metal traces were confirmed to carry over to the vapor produced by the device.

Chromium, nickel and manganese were the most concerning of the metals present in the e-cigarette aerosols, with the research finding the emission rates for many of these metals were equal to, or even higher than, conventional cigarette smoke. Chromium, nickel, and cadmium all exhibited higher emission rates that traditional cigarettes, while the concentration of lead in some of the e-cigarette aerosol samples was found to be similar to levels seen in cigarettes.

"It's important for the FDA, 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," says study senior author Ana María Rule.

Strangely enough, the metal concentrations in the aerosols studied were higher for e-cigarette devices that had their coils changed frequently, leading to the conclusion that, the newer the coil, the more it potentially leeched metals.

The actual health effects of these exposure levels are still unknown and the researchers are planning further research into the impacts on humans, but many of the median aerosol concentrations identified in the study did approach or exceed the safe limits defined by the Environmental Protection Agency.

The study is the latest in a growing body of research that suggests e-cigarettes are not necessarily a completely healthy or safe alternative to conventional cigarette smoking. The long-term health effects of "vaping" will not be known for some years, but it is becoming increasingly clear that although e-cigarettes may not cause the same type of damage to a human body as traditional cigarettes, they are certainly not harmless alternatives.

The research was published in the journal Environmental Health Perspectives.