TL;DR: Small study of only 3 out of 100 brands on the market, so limited inference can be drawn but cheap construction leaches toxic substances into the liquid in ways that older non-disposable vapes don’t. In terms of health risk non-disposable vapes are best followed by a tie between traditional cigarettes and disposable vapes.

The scientists analyzed the metal and metalloids inside seven types of disposable devices from three of the most popular brands. Using an instrument to activate the disposable e-cigarettes and heat the internal liquid, they created between 500 and 1,500 puffs for each device. They found:

• Some devices emitted surprisingly high concentrations of elements in the vapor, including antimony and lead.
• Levels of chromium, nickel and antimony increased as the number of puffs increased.
• Most of the disposable e-cigarettes tested released markedly higher amounts of metals and metalloids into vapors than earlier, refillable vapes.

The scientists then took apart the devices to trace the sources of the metals.

“We found that these disposable devices have toxins already present in the e-liquid, or they’re leaching quite extensively from their components into e-liquids and ultimately transferred to the smoke,” Salazar said.