How much is the safely tolerated value of fluoride (mg F/Kg)
Certainly lethal dose (CLD) - 32-64 mg F /Kg body weight
Safely tolerated dose (STD) - 8-16 mg F / kg body weight (1/4th of CLD)

Also note these two important values 

Probable toxic dose (PTD)- 2mg F/ Kg body weight
Minimum toxic dose (MTD)- 5-6 mg F/ Kg body weight.
4-Feb
8-Apr
16-Aug
32-64