Calcium tetraborate

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

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 calcium 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 calcium 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 calcium 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 calcium metaborate is proposed for this endpoint for the REACH registration of calcium tetraborate.

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Validity criteria fulfilled:

yes

Conclusions:

In conclusion, exposure of Daphnia magna to calcium tetraborate is expected to have no effect on the immobility observed.

Executive summary:

A study was conducted using calcium metaborate to evaluate the acute toxic effects on the mobility of Daphnia magna during an exposure period of 48 hours. The study was performed according to OECD 202. No immobility or other effects were observed in the control and at any of the test concentrations throughout the study.

In the environment, all calcium 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 calcium borate substances.  

 

Therefore, calcium tetraborate will exhibit the same acute toxicity effects on Daphnia magna. In conclusion, exposure of Daphnia magna to calcium tetraborate is expected to have no effect on the immobility observed.

Description of key information

No immobility or other effects were observed in the control and at any of the test concentrations throughout a study on Daphnia magna exposed to calcium metaborate. In the environment, all calcium borate substances in the category will rapidly dissociate and release the same common compound, boric acid as a result of relevant transformation pathways (e.g. hydrolysis) at environmentally relevant conditions (i.e., pH and concentration). No effects on mobility are therefore expected for Daphnia magna exposed to calcium tetraborate. A value of >100 mg/L is also reported for the EC50.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

100 mg/L