THC-Free CBD Isolate become THC CBD Isolate in acidic environment?

There is information out there stating that if you make CBD isolate acidic then you can convert it to containing THC.  Is this true?

If true:

1. does that mean that I should not use Citric Acid as a preservative in my cosmetic formulations containing CBD isolate?
2. can I use an acid, are there limits?