Reaction products of boric acid and lithium hydroxide

Toxicity to microorganisms

Link to relevant study record(s)

Reference

Endpoint:

activated sludge respiration inhibition testing

Type of information:

read-across based on grouping of substances (category approach)

Adequacy of study:

key study

Justification for type of information:

In the environment, all lithium borate substances in the category 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 of all the lithium borate substances.

Literature evidence is documented in the attached category approach document.

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).

Based on existing information sourced from the scientific and regulatory literature it is concluded that all the lithium borate substances in this category are expected to react similarly in the environment, forming boric acid if exposed to water or moist soils in the environment. As a result, read-across to dilithium tetraborate is proposed for this endpoint for the REACH registration of the UVCB-Reaction products of boric acid and lithium hydroxide.

Key result

Duration:

3 h

Dose descriptor:

other: ELR50

Effect conc.:

> 1 000 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Key result

Duration:

3 h

Dose descriptor:

other: ELR10

Effect conc.:

440 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Duration:

3 h

Dose descriptor:

other: ELR20

Effect conc.:

813 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

inhibition of total respiration

Conclusions:

The UVCB-Reaction products of boric acid and lithium hydroxide is not expected to be toxic to waste water bacteria (activated sludge) at or below a loading rate of 320 mg/L (NOELR).

Executive summary:

In a OECD 209 test, dilithium tetraborate was not toxic to waste water bacteria (activated sludge) at or below a loading rate of 320 mg/L (NOELR).

As all lithium borate substances in the category rapidly dissociate and release the same common compound, boric acid in environmental systems, then any variations in structure between the substances are not expected to lead to any changes in the toxicity of the substances to activated sludge. It is therefore expected that the UVCB-Reaction products of boric acid and lithium hydroxide is not toxic to waste water bacteria (activated sludge) as well.

Description of key information

In a OECD 209 test, dilithium tetraborate was not toxic to waste water bacteria (activated sludge) at or below a loading rate of 320 mg/L (NOELR).

As all lithium borate substances in the category rapidly dissociate and release the same common compound, boric acid in environmental systems, then any variations in structure between the substances are not expected to lead to any changes in the toxicity of the substances to activated sludge.It is therefore expected that the UVCB-Reaction products of boric acid and lithium hydroxide is not toxic to waste water bacteria (activated sludge) as well.

Key value for chemical safety assessment

EC50 for microorganisms:

1 000 mg/L

EC10 or NOEC for microorganisms:

440 mg/L