Reaction products of boric acid and calcium dihydroxide and lithium hydroxide

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

key study

Justification for type of information:

The UVCB - Reaction products of boric acid and calcium dihydroxide and lithium hydroxide (EC # 701-453-3) has structural similarities to two already established categories: lithium salts of the oxyacids of boron (B); and calcium salts of the oxyacids of boron (B). Dilithium tetraborate (EC# 234-514-3) (source substance #1) and calcium metaborate (EC# 237-224-5) (source substance #2) will be used to predict the properties for the target substance.
The hydrolysis theoretical statement prepared for dilithium tetraborate is appropriate for the categories: lithium salts of the oxyacids of boron (B); and calcium salts of the oxyacids of boron (B), since in the environment, all substances in these categories rapidly dissociate and release the same common compound, boric acid as a result of relevant transformation pathways (e.g. hydrolytic, oxidative, digestive or metabolic) at environmentally relevant conditions (i.e., pH and concentration). This boric acid component of the salt is expected to drive the ecotoxicological and environmental fate properties.
Read-across to the hydrolysis theoretical statement for dilithium tetraborate is therefore proposed.

To summarise, 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]-. Therefore at higher concentrations and pH levels greater than 9.2, the borate anion [B(OH)4]- becomes predominant.
B(OH)3 + 2H2O¿[B(OH)4]- + H3O+

Therefore, at the near neutral pH of most environmental and ecotoxicological systems and at low concentrations (<0.025 mol B/L), the neutral mononuclear species (B(OH)3) will dominate and only a small proportion of boron will exist as the borate monoanion, B(OH)4- (WHO, 1998).
In the Transitional Annex XV dossier for Boric Acid (Boric acid crude natural) submitted by Austria, the following statement is provided for the hydrolysis endpoint: “Boric acid is an inorganic compound and does not have any chemical bonds prone to hydrolysis. Hydrolysis is therefore not a relevant degradation pathway for boric acid under environmentally relevant conditions”. Therefore, once dilithium tetraborate or any of the other lithium/calcium borate substances have transformed to boric acid in water, no further hydrolysis is anticipated.
Based on existing information sourced from the scientific and regulatory literature it is concluded that hydrolysis testing is not necessary for all the lithium/calcium borate substances in this category. These substances are expected to form boric acid if exposed to water or moist soils in the environment. Boric acid is extremely stable and is not susceptible to hydrolysis in environmental media.

Reason / purpose for cross-reference:

read-across source

Transformation products:

not measured

Key result

Remarks on result:

not measured/tested

Remarks:

Based on existing information sourced from the scientific and regulatory literature it is concluded that hydrolysis testing is not necessary for dilithium tetraborate. These substances are expected to form boric acid if exposed to water or moist soils in the environment. Boric acid is extremely stable and is not susceptible to hydrolysis in environmental media.

Validity criteria fulfilled:

yes

Conclusions:

Based on existing information sourced from the scientific and regulatory literature it is concluded that hydrolysis testing is not necessary for the lithium/calcium borate substances in these categories. These substances are expected to form boric acid if exposed to water or moist soils in the environment. Boric acid is extremely stable and is not susceptible to hydrolysis in environmental media.

Executive summary:

The hydrolysis theoretical statement prepared for dilithium tetraborate is appropriate for all lithium/calcium borates in these categories  including the UVCB - Reaction products of boric acid and calcium dihydroxide and lithium hydroxide. Based on existing information sourced from the scientific and regulatory literature it is concluded that hydrolysis testing is not necessary for all the lithium/calcium borate substances in these categories. These substances are expected to form boric acid if exposed to water or moist soils in the environment. Boric acid is extremely stable and is not susceptible to hydrolysis in environmental media.

Description of key information

Based on existing information sourced from the scientific and regulatory literature it is concluded that hydrolysis testing is not necessary. Reaction products of boric acid and calcium dihydroxide and lithium hydroxide is expected to form boric acid if exposed to water or moist soils in the environment. Boric acid is extremely stable and is not susceptible to hydrolysis in environmental media.