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Administrative data

Description of key information

Acute oral studies have been performed with potassium tetraborate, disodium tetraborate, sodium tetraborate penthydrate and sodium tetraborate decahydrate. Acute dermal and inhalation studies have been performed with disodium tetraborate pentahydrate and disodium tetraborate decahydrate. Experimental data showed low acute toxicity to dipotassium tetraborate.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Dose descriptor:
LD50
3 690 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion
Dose descriptor:
discriminating conc.
2 030 mg/m³

Acute toxicity: via dermal route

Endpoint conclusion
Dose descriptor:
discriminating dose
2 000 mg/kg bw

Additional information

LD50 values of >2000 mg/kg was recorded for the oral route for potassium tetraborate and for the dermal routes for sodium tetraborate pentahydrate and disodium tetraborate decahydrate. An LD50 value > 2 mg/L was recorded for the acute inhalation study with disodium tetraborate decahydrate and disodium tetraborate pentahydrate. The inhalation figure represents the highest attainable concentration.

One acute oral toxicity study was conducted on potassium tetraborate in rats. The acute oral LD50 of the test substance in male albino rats was found to be 3.69 g/kg with 95 % confidence limits of 2.71 - 5.01 g/kg bw. (Shipp & Young 1975).

Potassium tetraborate is of low acute toxicity. Although some of the acute oral studies were not of modern standards and were performed prior to the introduction of GLP, they are reproducible across a number of studies and species and of acceptable quality. For acute dermal and acute inhalation some studies do meet the modern GLP standard.

The following acute oral data were obtained:

Potassium tetraborate: 3690 mg/kg

The following acute inhalation data were obtained:

No acute inhalation studies of dipotassium tetraborates have been conducted. Studies were conducted on an analogue substance

Disodium Tetraborate Pentahydrate: >2040 mg (302 mg B) /m3

Disodium Tetraborate Decahydrate: >2030 mg (300 mg B) /m3

The following acute dermal data were obtained:

No acute dermal studies of dipotassium tetraborates have been conducted. Studies were conducted on an analogue substance

Sodium Tetraborate Pentahydrate: >2000 mg/kg bw (296 mg B/kg)

Read Across

A number of these studies were conducted on an analogue substance. Read-across is justified on the following basis:

In aqueous solutions at physiological and acidic pH, low concentrations of simple inorganic borates such as boric acid B(OH)3, potassium pentaborate (K2B10O16.8H2O), potassium tetraborate (K2B4O7.4H2O), disodium tetraborate decahydrate (Na2B4O7.10H2O; borax), disodium tetraborate pentahydrate (Na2B4O7.5H2O; borax pentahydrate), boric oxide (B2O3) and disodium octaborate tetrahydrate (Na2B8O13.4H2O) will predominantly exist as undissociated boric acid. Above pH 9 the metaborate anion (B(OH)4-) becomes the main species in solution (WHO, 1998). This leads to the conclusion that the main species in the plasma of mammals and in the environment is undissociated boric acid. Since other borates dissociate to form boric acid in aqueous solutions, they too can be considered to exist as undissociated boric acid under the same conditions.

For comparative purposes, exposures to borates are often expressed in terms of boron (B) equivalents based on the fraction of boron in the source substance on a molecular weight basis. Some studies express dose in terms of B, whereas other studies express the dose in units of boric acid. Since the systemic effects and some of the local effects can be traced back to boric acid, results from one substance can be transferred to also evaluate the another substance on the basis of boron equivalents. Therefore data obtained from studies with these borates can be read across in the human health assessment for each individual substance. Conversion factors are given in the table under CSR section 5.1.3, which corresponds to IUCLID section 7.1 (toxicokinetics, metabolism and distribution endpoint summary).

References:

WHO. Guidelines for drinking-water quality, Addendum to Volume 1, 1998

Justification for classification or non-classification

Dipotassium tetraborate is not classified for the oral, dermal or inhalation routes, as the LD50 values exceed the limit for classification. No acute inhalation or dermal toxicity studies with dipotassium tetraborate were available, however theLD50 values for the dermal and inhalation routes for the disodium tetraborates exceed the limit for classification.