They only classed heating coil material by three types and two of them are pretty open ended. :/ Second paragraph of page 2:

type of coil (self-reported by the participants and categorized as Kanthal, other/combination, or unknown)

"Results, Metal Detection" Page 3

Of the 15 elements analyzed, with results included in Table 1, four (As, Ti, U, and W) were excluded from further analyses shown in Tables 2–8 due to low detection in a majority of the samples. As, Ti, and U were detected in less than 20% of all sample types and W was detected in less than 20% of dispenser and aerosol samples.

(As=arsenic, Ti=titanium, U=uranium, W=tungsten)

"Aerosol Metal Concentrations" Page 6

We focus on Ni, Cr, Pb, Mn, and As because, due to their toxicity when found in aerosols, these compounds have health-based limit concentrations. Ni concentrations ranged from 4:35 × 10−6 to 1:12 × 10−1 (median 4:44 × 10−4 Þ mg=m3 , and 57% of e-cigarette aerosol samples exceeded the Agency for Toxic Substances Disease Registry (ATSDR 2016) daily chronic minimum risk level (MRL) for Ni of 2:00 × 10−4 mg=m3.

Pb concentrations ranged from 1:49 × 10−6 to 2:75 × 10−2 (median 1:06 × 10−4Þ mg=m3, with 48% of aerosol samples exceeding the U.S. EPA National Ambient Air Quality Standard (NAAQS) (U.S. EPA 2016) of 1:50 × 10−4 mg=m3 and 11% exceeding the standard in nonattainment areas of 1:50 × 10−3 mg=m3. Mn concentrations ranged from 1:39 × 10−6 to 1:42 × 10−3 (median 1:97 × 10−5Þ mg=m3; 14% of samples exceeded the daily Mn MRL of 3:00 × 10−4 mg=m3 (ATSDR 2012b) and 75% exceeded the U.S. EPA daily cancer reference concentration (RfC) of 6:00 × 10−6 mg=m3 (U.S. EPA 2012). Arsenic concentrations, calculated only among the 10 aerosol samples (17.9%) with detectable arsenic (data not shown) ranged from 7:72 × 10−6 to 1:04 × 10−3 (median 1:50 × 10−4Þ mg=m3. All other metals investigated were also found in concentrations spanning three to four orders of magnitude (Figure 1) in the condensed aerosol, which would translate to several orders of magnitude in the air using Equation 1.

Discussion: (starts page 7, continues)

In this assessment of metal concentrations in samples collected from tank-style devices of daily e-cigarette users in Maryland, we found that, for most metals, concentrations were markedly higher in samples collected from the tank and the aerosol compared with those collected from the refilling dispenser. Dramatic increases were observed in tank samples for Cr, Cu, Ni, Pb, and Zn concentrations (more than 35 times higher than in the dispenser samples) as well as in aerosol samples for Pb and Zn (more than 25 times higher than in the dispenser samples) and for Cr, Ni, and Sn (more than 6 times higher than in the dispenser samples). For Mn, the concentrations in tank and aerosol samples were 19.6 and 1.93 times higher than the dispenser samples respectively. For Al, Cd, and Sb, the concentrations were between 2.30 and 4.65 times higher in the tank and between 1.60 and 3.58 times higher in the aerosol compared with the dispenser samples. The finding of Pb in e-cigarette aerosol samples, a metal not listed among the components of heating coils but that can be present in metal alloys, is of major concern both directly for the consumer as well as for those involuntarily exposed to e-cigarette aerosol, especially children.

As = arsenic, Cr = chromium, Cu = copper, Mn = manganese, Ni = nickel, Pb = lead, Zn = zinc.

The bolded section is exactly what happens when a US company orders a coil from a Chinese manufacturer to slap their brand on, not specifying a material Grade or purity. The problem is compounded when the company neglects to test the materials at a material analysis laboratory. They end up with an alloy with fucking lead in it and you end up vaporizing off it and inhaling lead through it. This is why it's REALLY IMPORTANT, FOLKS, to purchase products made from quality materials and preferably, from a company that proves it, with TEST RESULTS THAT SPECIFY THE TYPE OF METAL USED SO YOU KNOW YOU AREN'T HEATING AND VAPORIZING OFF LEAD.