I wanted to make a few quick points (and note that I am equally as interested in the answer from Imagine on the contents).
my disclaimer is that I am no expert but wanted to say that one, I found employees to work at a sylica mill, processing thingee (notice my technical apptitude). This plant took large fragments of sylica and would mill it into smaller sizes for various uses, including toothpaste which you will see is on the list of things sylica is used in. None of the workers wore masks and spent 8 hours or more a day in the dust. Additionally, the articles that are mentioned are talking about dust (this part is my opinion only); with the wicks, how could dust be created and inhaled when wet? And, taking something that someone found on the internet and posted on a forum that may or may not be related to the subject that is being discussed or the poster really knowing...............
My second point, and I am sure this will rub a few the wrong way..............we buy PVs that are not regulated at all, mostly manufactured in China where they use lead based paints in children's toys (something that IS regulated), ingest/inhale juice which has no ingredient list (also not regulated) and then surprised that there could be something dangerous in it????? Even if the sylica is non-harmfull; the plastic these things are made from, the pigment to color them, the silicone processing, the contents of the flavoring, the nicotine portion of the juice and its ingredients, the pg, the vg, the exposure to extended battery use and peanut butter injected into rats could cause you all cancer (obviously hope that it doesnt).
just a thought
Im fully aware of everything in your second point, thats PRECISELY why im DIYing my own juices, and currently trying to find as much information about possible hazard of vartious, carts, cartos, tanks, ces, clearos, etc to decide which i personally believe will be best.