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During the hydrolysis of boron trifluoride phosphate, phosphoric acid is released and an acidic reactive mixture of boric acid, hydroxyfluoroboric acid, hydrofluoric acid, tetrafluoroboric acid and, depending on the pH value, the respective anions are produced. In aqueous solution, tetrafluoroboric acid is partly hydrolysed to hydroxyfluoroboric acid.

For boron trifluoride, measurement of fluoride ion production over a range of pH values (1.2 to 9) indicated a hydrolytic half-life time of less than 30 minutes which could be confirmed by the subsequent analysis of boric acid by titration (see also IUCLID chapter 5.1.2). The risk associated to dehydrated boron trifluoride when released into water can be assessed based upon the hazards of its breakdown products in water: boric acid and tetrafluoroboric acid.

With regards to boric acid, a study showed that at each of pH 1.2, 4, 7 and 9 and 50 ± 0.5 ºC, less than 10 % hydrolysis had occurred after 5 days, equivalent to a half-life of greater than 1 year under environmental conditions (25°C). Thus Boric acid was determined to be hydrolytically stable under acidic, neutral and basic conditions.

With regards to tetrafluoroborate, it is apparent that tetrafluoroborate hydrolyses under environmental conditions, forming boric acid and, predominantly, partially hydrolysed fluoroborate species (i.e. fluorine and hydronium ions) resulting from hydrogen fluoride which is absorbed into the body and ionises (>99.99%). For that reason, HF is not expected at significant amounts as it occurs in the systemic circulation only as free ionic or as organically bound fluoride. Boric acid is readily absorbed orally and by inhalation; no dermal absorption (< 0.5%) occurrs. It is then rapidly distributed through body water and is not metabolised.

In conclusion, for the endpoints for which no substance-specific data for boron trifluoride phosphate were available, read-across from the hydrolysis products boron trifluoride (and boron trifluoride dihydrate, respectively) and phosphoric acid is considered acceptable in accordance with REACH Annex XI, section 1.5.

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