Reaction products of boric acid and calcium dihydroxide and lithium hydroxide

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 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.


In the environment, all lithium/calcium borate substances in the 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.

Literature evidence is documented in the attached category approach document and states that several lithium and calcium borates are precursors of boric acid.

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/calcium borate substances in these categories 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 Reaction products of boric acid and calcium dihydroxide and lithium hydroxide.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

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:

EC50

Effect conc.:

36 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: yield inhibition

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

32 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: based on biological

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

10 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

growth rate

Remarks on result:

other: based on statistical significance

Duration:

72 h

Dose descriptor:

NOEC

Effect conc.:

18 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

other: yield inhibition

Remarks on result:

other: based on biological

Validity criteria fulfilled:

yes

Conclusions:

In conclusion, Reaction products of boric acid and calcium dihydroxide and lithium hydroxide is expected to reduce the growth rate and inhibit the yield of this fresh water algae species significantly at test concentrations of 18 mg/L and higher in an analogous manner to dilithium tetraborate.

Executive summary:

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

 

Growth rate and yield were in the range of the controls at the lowest test concentration during the 72-hour test period, whereas at higher concentrations growth rate and yield were increasingly inhibited. Statistically significant inhibition of growth rate and yield was found at test concentrations of 18 mg/L and higher. The inhibition of growth rate observed at the concentrations of 18 and 32 mg/L was however, considered biologically not relevant (i.e. were <10%). Therefore, the NOEC (inhibition of growth rate based on biological relevance) = 32 mg/L.

 

In the environment, all lithium/calcium borate 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 of all the lithium/calcium borate substances.  

The target UVCB substance has a higher precursor molar ratio for lithium hydroxide than for calcium hydroxide, and therefore the precautionary principle should be applied and read across from dilithium tetraborate where relevant to consider the worst case.

Therefore, Reaction products of boric acid and calcium dihydroxide and lithium hydroxide will inhibit the growth and yield of Pseudokirchneriella subcapitata in a similar manner. In conclusion, Reaction products of boric acid and calcium dihydroxide and lithium hydroxide is expected to reduce the growth rate and inhibit the yield of this fresh water algae species significantly at a nominal test concentration of 18 mg/L or greater.

 

Description of key information

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

 

Growth rate and yield were in the range of the controls at the lowest test concentration during the 72-hour test period, whereas at higher concentrations growth rate and yield were increasingly inhibited. Statistically significant inhibition of growth rate and yield was found at test concentrations of 18 mg/L and higher.

 

In the environment, all lithium/calcium borate substances in these categories rapidly dissociate and release the same common compound, boric acid as a result of relevant transformation pathways. Therefore, Reaction products of boric acid and calcium dihydroxide and lithium hydroxide will inhibit the growth and yield of Pseudokirchneriella subcapitata in a similar manner. In conclusion, Reaction products of boric acid and calcium dihydroxide and lithium hydroxide is expected to reduce the growth rate and inhibit the yield of this fresh water algae species significantly at a nominal test concentration of 18 mg/L or greater.

Key value for chemical safety assessment

EC50 for freshwater algae:

100 mg/L

EC10 or NOEC for freshwater algae:

32 mg/L