By Robert Preidt
"We do not know if these levels are dangerous, but their presence is troubling and could mean that the metals end up in the aerosol that e-cigarette users inhale," said study leader Ana Maria Rule, of Johns Hopkins Bloomberg School of Public Health in Baltimore.
Rule is an assistant scientist in the department of environmental health and engineering.
She and her colleagues analyzed the liquid of five brands of so-called first-generation e-cigarettes, which resemble traditional cigarettes. (Newer e-cigarettes look like small cassette recorders with mouthpieces.)
The researchers found liquids in those brands contained the heavy metals cadmium, chromium, lead, manganese and nickel. These metals are toxic when inhaled, the researchers said.
In first-generation e-cigarettes, the cartridge of liquid is stored in close contact with the heating coil. When heated, the liquid creates the aerosol, or vapor, that users inhale. The researchers believe this heating coil is the main source of the dangerous metals.
"Perhaps regulators might want to look into an alternative material for e-cigarette heating coils," Rule said in a Hopkins news release.
The researchers did not examine the possible presence of the five metals in the aerosol.
Currently, the U.S. Food and Drug Administration requires e-cigarette makers to submit ingredient lists and information about potentially harmful ingredients, including four of the five metals detected in this study -- nickel, lead, chromium and cadmium.
The agency has studied but not yet issued proposed rules on e-cigarette labeling.
"It was striking, the varying degrees to which the metals were present in the liquid," Rule said. "This suggests that the FDA should consider regulating the quality control of e-cigarette devices along with the ingredients found in e-cigarette liquids."
The findings were published recently in the journal Environmental Research.