sodium borate (Borax)
Boric acid and sodium borate (Borax) are estimated to have a fatal dose from 0.1 to 0.5g/kg. These substances are toxic to all cells, and have a slow excretion rate through the kidneys. Kidney toxicity is the greatest, with liver fatty degeneration, cerebral edema, and gastroenteritis. Boric acid solutions used as an eye wash or on abraded skin are known to be especially toxic to infants, especially after repeated use due to its slow elimination rate.
According to Handbook of Poisoning, Robert H. Dreisback, eighth edition, p.314, boric acid, sodium borate, and sodium perborate are estimated to have a fatal dose from 0.1 to 0.5g/kg. That’s about one hundreth to five hundredths of a teaspoon per pound of body weight, so a teaspoon ingested could be toxic to a 100 pound body.
According to Goodman and Gillman’s: The Pharmacological Basis of Therapeutics, 6th edition, chapter on Antiseptics and Disinfectants, page 971 says these borates are toxic to all cells, and have a slow excretion rate through the kidneys. Kidney toxicity is the greatest danger, but they also cause liver degeneration, swelling of the brain, and gastroenteritis. Especially dangerous to infants.