Calcium tetraborate

Endpoint summary

Key value for chemical safety assessment

Genetic toxicity in vitro

Description of key information

The OECD TG 471 in vitro study (Gijesbrechts, 2017) was used to determine the potential of Calcium metaborate to induce reverse mutations at the histidine locus in several strains of Salmonella typhimurium (S. typhimurium; TA98, TA100, TA1535, and TA1537), and at the tryptophan locus of Escherichiacoli (E. coli) strain WP2uvrA in the presence or absence of an exogenous mammalian metabolic activation system (S9).Since 2.4- to 3.0-fold dose-related increases were observed both in the absence and presence of S9-mix in the tester strains TA100 and WP2uvrA, the number of revertants were above the laboratory historical control data range and the results were observed in the direct plate and pre-incubation assay, these increases are considered biologically relevant and the test item is mutagenic.

 

The same mutagenic response is expected for calcium tetraborate since variations in structure (trigonal vs tetrahedral) between the substances are not expected to lead to any changes as at physiological pH as all the substances dissociate to provide the same common compounds. 

Link to relevant study records

Reference

Endpoint:

in vitro gene mutation study in bacteria

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

At physiological pH, all category members dissociate and release boric acid and calcium ions as a result of relevant transformation pathways. It will the boric acid component of the substances which will drive the mammalian toxicity endpoints. In order to minimise animal testing, only one substance in the category was tested, calcium metaborate. For all other substances in the category, read-across is proposed.

Species / strain:

S. typhimurium TA 1535

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

In both the direct assay and pre-incubation assay

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Cytotoxicity, as evidenced by a reduction of the bacterial background lawn, was observed at dose levels of 750 μg/plate and upwards in the absence of S9-mix in the pre-incubation methods.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 1537

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

In both the direct assay and pre-incubation assay

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Cytotoxicity, as evidenced by a reduction of the bacterial background lawn, was observed at dose levels of 750 μg/plate and upwards in the absence of S9-mix in the pre-incubation methods.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 98

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

In both the direct assay and pre-incubation assay

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Cytotoxicity, as evidenced by a reduction of the bacterial background lawn, was observed at dose levels of 750 μg/plate and upwards in the absence of S9-mix in the pre-incubation methods.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with and without

Genotoxicity:

negative

Remarks:

In the direct plate assay

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Cytotoxicity, as evidenced by a reduction of the bacterial background lawn, was observed at dose levels of 750 μg/plate and upwards in the absence of S9-mix in the pre-incubation methods.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

E. coli WP2 uvr A

Metabolic activation:

with and without

Genotoxicity:

positive

Remarks:

In both the direct assay and pre-incubation assay

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Cytotoxicity, as evidenced by a reduction of the bacterial background lawn, was observed at dose levels of 750 μg/plate and upwards in the absence of S9-mix in the pre-incubation methods.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Species / strain:

S. typhimurium TA 100

Metabolic activation:

with

Genotoxicity:

positive

Remarks:

In the pre-incubation assay only

Cytotoxicity / choice of top concentrations:

cytotoxicity

Remarks:

Cytotoxicity, as evidenced by a reduction of the bacterial background lawn, was observed at dose levels of 750 μg/plate and upwards in the absence of S9-mix in the pre-incubation methods.

Vehicle controls validity:

valid

Untreated negative controls validity:

valid

Positive controls validity:

valid

Conclusions:

Based on the results of this OECD TG 471 study it is concluded that calcium metaborate is mutagenic in the Salmonella typhimurium reverse mutation assay and in the Escherichia coli reverse mutation assay. Read-across to these results are proposed for calcium tetraborate since at physiological pH, both substances will dissociate and release boric acid and calcium ions as a result of relevant transformation pathways. The same mutagenic effects are therefore expected.

Executive summary:

The OECD TG 471 in vitro study was used to determine the potential of calcium metaborate to induce reverse mutations at the histidine locus in several strains of Salmonellatyphimurium (S. typhimurium; TA98, TA100, TA1535, and TA1537), and at the tryptophan locus ofEscherichiacoli (E. coli) strain WP2uvrA in the presence or absence of an exogenous mammalian metabolic activation system (S9).

Since 2.4- to 3.0-fold dose-related increases were observed both in the absence and presence of S9-mix in the tester strains TA100 and WP2uvrA, the number of revertants were above the laboratory historical control data range and the results were observed in the direct plate and pre-incubation assay, these increases are considered biologically relevant and the test item is mutagenic.

Read-across to these results are proposed for calcium tetraborate since at physiological pH, all category members dissociate and release boric acid and calcium ions as a result of relevant transformation pathways.  Variations in structure (trigonal vs tetrahedral) between the substances are not expected to lead to any changes to the results. As the results were equivocal, a testing proposal is submitted for calcium metaborate for further investigations of the mutagenic effect of these calcium borates.

Endpoint conclusion

Endpoint conclusion:

adverse effect observed (positive)

Justification for classification or non-classification

Insufficient data is currently available to ascertain the mutagenic potential of calcium tetraborate.