Boric acid, also called boracic acid or orthoboric acid or Acidum Boricum, is a weak acid often used as an antiseptic, insecticide, flame retardant, in nuclear power plants to control the fission rate of uranium, and as a precursor of other chemical compounds. It exists in the form of colorless crystals or a white powder and dissolves in water.

Based on mammal median lethal dose (LD50) rating of 2,660 mg/kg body mass, boric acid is poisonous if taken internally or inhaled. However, it is generally considered to be not much more toxic than table salt.[3] The Thirteenth 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. The LD50 of sodium chloride is reported to be 3.75 g/kg in rats according to the Merck Index.

Long term exposure to boric acid may be of more concern. Although it does not appear to be carcinogenic, studies in dogs have attributed testicular atrophy after exposure to 32 mg/kg bw/day for 90 days. This level is far lower than the LD50.[4]

According to boric acid IUCLID Dataset published by the European Commission, boric acid in high doses shows significant developmental toxicity and teratogenicity in rabbit, rat, and mouse fetus such as cardiovascular defects, skeletal variations, mild renal lesions.[5] As a consequence, in August 2008, in the 30th ATP to EU directive 67/548/EEC, the EC decided to amend its classification as reprotoxic cat. 2 and R60 (may impair fertility) R61 (may cause harm to the unborn child).

REFERENCES:
http://en.wikipedia.org/wiki/Boric_acid#Toxicology