Trust me when I say: use KGD or similar for a week or two then wick something up with cotton balls. Youll taste the difference! I was like "Blech!!" The first couple hits on a cotton ball wick are terrible after using KGD for a couple months.
As to your question, maybe someone has a Geiger Counter they can pass over their box of KGD. LOL!!!! Mine doesn't have a green glow when you turn the lights out! I wouldn't really worry about that...
Hah! You know, I work with a bunch of nuclear engineers, and could easily have them pass a Geiger counter over my pack of Muji cotton which will be here any day now.
That said, I have tried both the KGD and the Muji. Both are equally good for vaping purposes. Same great wicking, no flavor being added. In fact, they basically look and feel the same too.
Because KGD received a pretty large response from the vaping community, the prices have started to rise. Muji, on the other hand, is still the same price. So, personally, I would get the Muji, and save yourself $5...
The Muji cotton, FWIW, is the same stuff being used in the Kanger OCC heads, just FYI.