Table 1.

List of studies and ranges of metal concentrations used in risk assessment in e-cigarettes.

Study.	Metric	Metals (Range)	Comments
Aerosol Studies
Williams 2013 [17]	Aerosol: μg/10 puffs	Cr (0.007)	Single brand/design. Cartomizer
		Ni (0.005)
		Mn (0.002)
		Pb (0.017)
		Cu (0.002)
		Zn (0.058)
		Sn (0.037)
		Al (0.394)
		Fe (0.52)
		Ba (0.012)
Goniewicz 2014 [19]	Aerosol: μg/10 puffs	Ni (0.007–0.019)	12 e-cigarettes from Poland and the UK
		Cd (0.001–0.015)
		Pb (0.002–0.038)
Mikheev 2016 [23]	Aerosol: ng/mg TPM	Cr (1.0–3.0)	Blu brand, 7 flavors
		Ni (0.1–0.2)
		Pb nd
		Cd nd
		Mn nm
		Cu (0.6–0.7)
		Zn (2.0–3.0)
		Sn (0.08–0.09)
		Sb (0.1–0.4)
		As (0.07–0.09)
Gaur 2019 [24]	Aerosol: μg/10 puffs	Cr (0.007–0.2)	Review of 12 studies
		Ni (0.005–0.007)
		Mn (0.002–0.035)
		Pb (0.002–0.038)
		Cd (0.0004–0.0146)
		Cu (0.011–2.2)
		Sn (0.036–6.0)
		Al (0.266–0.394)
Liquid Studies
Hess 2017 [15]	Liquid: μg/L	Cr (56–726)	Cigalike refill liquids, N = 5
		Ni (58–15400)
		Mn (26–918)
		Pb (4.98–1630)
		Cd (0.2–12.4)
Olmedo 2018 [16]	Liquid: μg/L	Cr (55.4)	Multiple types of device. N = 56 aerosols and dispensers, N = 49 tanks
		Ni (233)
		Mn (31.9)
		Pb (40.2)
		Cu (148)
		Zn (426)
		Sn (20.3)
		Cd (0.126)
		Sb (0.563)
		Al (31.2)
		Fe (382)
Kamilari 2018 [20]	Liquid: μg/L	Cr (4–32)	Refill liquids, N = 22
		Ni (2–92)
		Pb (1–11)
		Cd (4.8–175)
		As (nd–4)
Zhao 2019 [22]	Liquid (from aerosol): μg/L	Cr (0.39–15.6)	Range of medians of 2 closed and 2 open devices
		Ni (1.3–2148)
		Mn (0.39–64)
		Pb (0.9–541)
		Cd (0.04–0.16)
		Cu (6.0–542)
		Sb (0.15–4.6)
		Sn (0.35–322)
		Zn (683–3114)
		Fe (3.4–153)
		Al (4.1–17.7)