>Boric acid is technically poisonous.  Lots of things are used to make things
>that are used topically that are not meant to be ingested.  But boric acid
>has a low toxicity rate compared to man made chemicals, with a lethal dose
>of 50 (about as low as you can get).
 
The lethal dose of boric acid is NOT 50 of anything.  The NAME of the test
is "Lethal Dose 50" (LD50) because that's the amount of the chemical in
question needed to kill 50% of the test population.  The actual lethal doses
for boric acid are listed below:
 
            TOXICITY:   LD50 (ORAL-RAT)(MG/KG)    -  2660
                        LD50 (SCU-RAT)(MG/KG)     -  1400
                        LD50 (IV-RAT) (MG/KG)     -  1330
 
Source:  http://www.chem.utah.edu/MSDS/B/BORIC_ACID
 
Yes, you are right, it is a very mild toxicity.
 
By the way, water (the type we drink) is TECHNICALLY poisonous, too.  Heck,
EVERYTHING is technically poisonous, when you get right down to it ... it
just depends how much of it you take!  Just for fun, I'm including the LD50
for water below:
 
            LD50 (IPR-MOUSE)(G/KG)          -  190
            LD50 (IV-MOUSE) (MG/KG)         -  25
 
Source:  http://www.chem.utah.edu/MSDS/W/WATER
 
Yup, that's a VERY mild toxicity!  ;->
 
To keep this ferret related, yes, boric acid is safe for flea killing.
Heck, it's gentle enough that they put it into contact lens solutions and
eye washes!  Just do not inhale it or ingest large quantities of it, please!
 
- Ela
[Posted in FML issue 2305]