The lethal dose of fluoride for 70 kg adult is:
CERTAINLY LETHAL DOSE (CLD) : 32 - 64 mg of fluoride/kg body wt.
SAFELY TOLERATED DOSE (STD) : 8 - 16 mg of fluoride/kg body wt.
Ref: Soben peter 5th edition pg no:280
32-64 mg of fluoride/kg body weight
50-60 mg of fluoride/kg body weight
30-70 mg of fluoride/kg body weight
60-80 mg of fluoride/kg body weight