Stainless steel is a metallic alloy known to contain at least 11% of chromium; chromium in solid stainless steel should not be regarded as a health hazard. Hexavalent chromium can be formed when performing “hot work” such as welding on stainless steel. In these situations, high temperatures involved in the process result in oxidation that converts the chromium to a hexavalent state. Hexavalent chromium is very toxic, is found in tobacco smoke, and is known to cause lung cancer. Hexavalent chromium formation during vaping has not been investigated, but it can be generated before use, when people oxidise the stainless steel wick/mesh by torching it until it glows red-hot. The real problem is that we do not know if this previous oxidizing process results in an instability of the chromium-ion bonds with subsequent release of toxic chromium even at normal operating temperatures. In absence of clear demonstration of hexavalent chromium in the aerosol of e-cigarettes, my personal advice is to use organic unprocessed wicks (e.g. cotton). –
Professor Riccardo Polosa