Here's the link to the NZ Ruyan cartridge study report.
http://healthnz.co.nz/RuyanCartridgeReport21-Oct-08.pdf
Conclusion. Based on the manufacturer’s information, the composition of the cartridge liquid is not hazardous to health, if used as intended.
I've read that the amount of nicotine absorbed by vaping is approximately 10% of what is absorbed by smoking. This is mainly due to the differences in the size of particulates in smoke vs. the nicotine in vapor droplets.
* Smoke particle size : 0.1 to 1 micron; PG mist droplet size : 1 to 5 micron.
This basically means the lungs have more capacity to absorb substances in smoke rather than vapor.
But could also be due to the amount of nicotine that is released in smoking vs. vaporizing.
This could explain why many vapors have a desire to vape more than they smoked. And another good reason to use a smoke juice with an adequate nicotine level if using as a substitute for smoking or in an effort to quit smoking.
In my case, and as a former pack a day smoker, the difference between 8-11mg e-liquid and 18-24mg is significant. The 8-11mg has me vaping all the time. The 18-24mg leaves me relatively satisfied and vaping about as much as I smoked.