 The Fourteenth Edition of the "Merck Index" indicates that the LD50 of boric acid is 5.14 g/kg for oral dosages given to rats, and that 5 to 20 g/kg has produced death in adult humans.For comparison's sake, the LD50 of salt is reported to be 3.75 g/kg in rats according to the "Merck Index".According to the Agency for Toxic Substances and Disease Registry, "The minimal lethal dose of ingested boron (as boric acid) was reported to be 2–3 g in infants, 5–6 g in children, and 15–20 g in adults.