I can tell you what’s new, but it takes a bit o ‘splainin’, so bear with me. (Those who know this part can skip ahead).
Legitimate THC cartridge (“cart”) mfrs have always used some form of diluting agent or “diluent.” High-purity extraction (by whatever method) yields a very thick, sticky substance, too thick to wick up on a cart’s heating element.
The traditional diluents – Vegetable Glycerin (VG), Propylene Glycol (PG) and Medium-Chain Triglyceride Oil (MCT Oil) all have fairly decent track records as vaporized inhalants. PG and VG are also used in eCigs, PG/VG mixes are the “fog juice” that SPFX guys in film and theater use, and all these things are food-safe, GRAS-listed.
They’re also very cheap.
Legitimate cart mfrs use as little diluent as possible - their wares will be lab-tested, and consumers don’t want over-diluted (“cut”) product.
Besides, using too much of any those diluents will thin the oil to the point it won’t wick properly, and consumers can see that it’s thin and over-diluted just by turning the cart over and watching the bubble move.
Black-market carts are sold primarily where recreational sales aren’t legally permitted (also the location of almost ALL the “vaping deaths”.)
You can buy empty, unfilled carts with slick-looking packaging all over, and online. Some are forgeries of legit brands, some just fictional.
And they almost all have some high THC percentage pre-printed on the pkg. (This is frequently a tell, since legit carts do testing on a per-batch basis, and add the results (usually via an applied sticker) after packaging.)
So you fill your empty carts with whatever goo you’ve got, but you still can’t over-dilute, since the customers, lacking any real data, still use thickness - how fast does the bubble move? - as a proxy for purity.
But last year or so, along comes a kewl new product - “Honey Cut” and “Clear Cut” and assorted plain-wrap imitators, usually in unlabeled Mason Jars.
These are proprietary mixtures - no ingredients disclosed. So no one really knows what’s in them, although the terms “food-safe” and “GRAS-listed” are sometimes mentioned. (One correspondent said a mfr he contacted said it was “mostly vitamins.”)
And these “cuts” are almost stupidly expensive. Brand name or plain-wrap knockoff, they retail at around $1000/liter.
Unlike the traditional diluents, you can massively cut your product - one mfr bragged “up to 75% diluent” without losing viscosity. “The bubble still doesn’t move!”, they proclaim.
The primary suspect seems to be Vit. A acetate, or “tocopheral acetate”. It’s been found in carts implicated in the deaths, and in damaged lungs. It fits all the clues – food-safe, GRAS-listed, a vitamin – and, when vaporized and inhaled, it can cause *lipoid pneumonia", in which the oil settling in the lungs disrupts the surfactant membrane of the alveoli and interferes with oxygen transport.
Lipoid pneumonia is a known hazard of a number of vaporized oils, including mineral oil, which was once used as stage fog with rather grim health consequences.
And lipoid pneumonia is what has lately started killing vapers.
There remain some uncertainties - Vit A acetate shouldn’t really vaporize at standard THC cart temps, so maybe there are some malfing carts involved. And given the range of possibilities, Vit.A may not be the ONLY troublesome ingredient, and the ingredients may vary by mfr…
VG and PG and MCT oil may not be absolutely safe, but they’ve never before caused this sort of damage, despite widespread use.
Proprietary black-market “cuts” seem a far more likely culprit.
(And fortunately, there’s no motive to use those in legitimate, lab-tested carts, so buyers at legitimate legal dispensaries are unlikely to have a problem. IMO.)