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In aqueous solutions at physiological and acidic pH, low concentrations of simple inorganic borates such as boric acid, disodium tetraborate decahydrate, disodium tetraborate pentahydrate, boric oxide and disodium octaborate tetrahydrate will predominantly exist as undissociated boric acid. At about pH 10 the metaborate anion (B(OH)4-) becomes the main species in solution (WHO, 1998). This leads to the conclusion that the main species in the plasma of mammals and in the environment is un-dissociated boric acid. Since other borates dissociate to form boric acid in aqueous solutions, they too can be considered to exist as un-dissociated boric acid under the same conditions.

The vapour pressure for boric acid is extremely low so volatilization is expected to be minimal. The exception is over the oceans, where evaporation of aerosols leads to small but measured quantities of boric acid vapour in the marine atmosphere. The solubility of such materials means that they are re-deposited into the oceans or as precipitation in coastal areas. Marine evaporation is estimated as 1.3 to 4.5 x 10^9 kg-boron per year globally (Argust, 1998, Park and Schlesinger, 2002).