SmokeyJoe had a link to a press release on this and I followed it to Addiction and the full article is available. On a skim it's full of good points to use for FDA comments and has 115 references to back up comments.
Electronic cigarettes: review of use, content, safety, effects on smokers and potential for harm and benefit - Hajek - 2014 - Addiction - Wiley Online Library
Electronic cigarettes: review of use, content, safety, effects on smokers and potential for harm and benefit - Hajek - 2014 - Addiction - Wiley Online Library