Registration Dossier

Environmental fate & pathways

Endpoint summary

Administrative data

Description of key information

Additional information

Inorganic borates (e.g., boric acid, sodium tetraborates) are soluble in water.. The chemical species present in solution depend on concentration and pH.

Only two soluble B species in ordinary soils can be expected (Adriano, 2001). The nonionized species, [B(OH)3], is the predominant species expected in soil solution. Boric acid, [B(OH)3], is a very weak, monobasic acid that acts as a Lewis acid by accepting a hydroxyl ion to form the borate anion, [B(OH)4]-. At pH greater than 9.2, [B(OH)4]- becomes predominant.

B(OH)3 + 2H2O ↔ [B(OH)4]- + H3O+              pKa = 9.2

In the pH range of 7 to 11, both species can be found. With higher boron concentrations (B > 0.025 M) and increasing pH also polymeric B forms can precipitate, which are commonly very rare and unstable in soils. Therefore, boric acid and borate ions are the predominant B-forms in the natural soil system (Power and Woods, 1997; de Vette et al., 2001).

Boron as a natural element is not degradable. However, boron and its inorganic compounds are subject to chemical transformation processes (adsorption, complexation, precipitation,fixation) once released to the environment. One consequence of the transformation is that the mobility/bioavailability and the potential for toxicity, induced by the borate species, is changed and in many cases reduced or even removed over time. Thus, these natural processes achieve a similar result as is sought in the demonstration of biotic and abiotic degradation of synthetic organic chemicals.