I am not reassured by these answers. As a former lab tech, I'm well aware that the lack of particles visible to the eye does not mean that they aren't there.
gthomspon, I just want to be better informed so that I can decide for myself which risks I'm willing to take. After all, this is the reason why I began vaping, to reduce my risk of dying. I don't want to inadvertently raise that risk again. I think these are legitimate questions that need to be asked. At least it is for me. This is something I care about.
I think it isn't safe to make assumptions. Assuming that everything synthetic is safe is as naive is assuming that everything natural is safe. Neither assumption is true and both are easily refuted. Hemlock, deadly nightshade, arsenic, and cyanide are all natural and deadly, for example. Some substances are not safe, and their origin as synthetic or natural is not a reliable indicator of safety or risk.
I am reading a monograph from
Smokeless Tobacco or Health: An International Perspective called
Chemical Composition of Smokeless Tobacco Products by Klaus T. Brunnemann and Dietrich Hoffman. Table 1 shows which carcinogenic agents are found in natural tobacco (NT). Some of the carcinogenic compounds that develop in tobacco is from air curing or fire curing, not from additives, as this paper also explains. The precusors for the carcinogenic compounds are "integral parts of the tobacco" (page 105). The phrase "natural tobacco" used in this monograph does not refer to cured tobacco, and now I wonder how it is meant when the phrase is used to refer to tobacco juice since so many of the flavoring compounds do not develop until the tobacco is cured, as explained in this monograph, and it's the cured tobacco flavor that is so sought after.
You are correct that certain flavor additives are carcinogenic, which also raises alarm bells for me. I don't wish to skip the tobacco only to get carcinogenic tobacco flavoring additives in my ejuice, if those are being used. How would we know?
After having skimmed through most of the monographs, I am not reassured that natural tobacco is so safe that I have no reason for concern if it's in my ejuice.