Speaking to NICNAS (National Industrial Chemicals Notification and Assessment Scheme) Australias governing body for safe chemical use in Australia.
I was told products containing boric acid have an S4 scheduling, in Australia S4 goods sold for human use must me sold under the advice of a pharmacist. For therapeutical goods, they must not contain more than 0.035% for topical and eye treatments.
This means that according to the Theropeutical Good Adminstration (tga) that levels above 35ppm of Boronic Acid is considered unsafe for human use and illegal for use in Australia. I have no reference to their findings or research, however this is a concern.