Reaction products of boric acid 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 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:

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, the UVCB-Reaction products of boric acid 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 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.  

 

Therefore, the UVCB-Reaction products of boric acid and lithium hydroxide will inhibit the growth and yield of Pseudokirchneriella subcapitata in a similar manner. In conclusion, lithium tetrahydroxyborate 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 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 borate substances in the category rapidly dissociate and release the same common compound, boric acid as a result of relevant transformation pathways. Therefore, lithium tetrahydroxyborate will inhibit the growth and yield of Pseudokirchneriella subcapitata in a similar manner. In conclusion, the UVCB-Reaction products of boric acid 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