The association of e-cigarette use with exposure to nickel and chromium: A preliminary study of non-invasive biomarkers

•E-cigarette heating coils are commonly made of Ni and Cr, known carcinogens.•Ni and Cr levels were detected in aerosol samples from e-cigarette devices of users.•These levels in aerosol were positively associated with Ni and Cr biomarker levels.•Increased use and consumption were also associated with Ni biomarker levels.•Findings demonstrate e-cigarette use as a relevant source of toxic metal exposure.