Calcium tetraborate

Toxicity to aquatic algae and cyanobacteria

Link to relevant study record(s)

Reference

Endpoint:

toxicity to aquatic algae and cyanobacteria

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.

Key result

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

79 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Duration:

72 h

Dose descriptor:

EC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Duration:

72 h

Dose descriptor:

EC10

Effect conc.:

92 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

cell number

Validity criteria fulfilled:

yes

Conclusions:

In conclusion, calcium tetraborate is expected to reduce the growth rate and inhibit the yield of this fresh water algae species significantly at a nominal test concentration of 100 mg/L.

Executive summary:

The effects of calcium metaborate on Pseudokirchneriella subcapitata were determined by an experimental study conducted according to OECD guideline No. 201.

Growth rates and yield were in the range of the control for concentrations up to 32 mg/L during the 72-hour test period, whereas they were reduced by 15 and 55%, respectively, at the highest test concentration at the end of the test. Statistically significant inhibition of growth rates and yield was found at test concentration of 100 mg/L.

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 inhibit the growth and yield of Pseudokirchneriella subcapitata in a similar manner. In conclusion, calcium tetraborate is expected to reduce the growth rate and inhibit the yield of this fresh water algae species significantly at a nominal test concentration of 100 mg/L.

Description of key information

The effects of calcium metaborate on Pseudokirchneriella subcapitata were determined by an experimental study conducted according to OECD guideline No. 201.

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 inhibit the growth and yield of Pseudokirchneriella subcapitata in a similar manner.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC50 for marine water algae:

100 mg/L

EC10 or NOEC for freshwater algae:

79 mg/L

EC10 or NOEC for marine water algae:

79 mg/L