Pentaboron sodium octaoxide

Endpoint summary

Description of key information

Acute oral studies have been performed with sodium metaborate tetrahydrate, sodium metaborate dihydrate, disodium tetraborate anhydrous, disodium tetraborate pentahydrate and disodium tetraborate decahydrate. Acute dermal and inhalation studies have been performed with disodium tetraborate pentahydrate and disodium tetraborate decahydrate.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

2 330 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Dose descriptor:

discriminating conc.

Value:

2 030 mg/m³ air

Acute toxicity: via dermal route

Endpoint conclusion

Dose descriptor:

discriminating dose

Value:

2 000 mg/kg bw

Additional information

No acute oral toxicity studies with Sodium Pentaborate have been conducted. LD50 values of >2000 mg/kg was recorded for the oral route for sodium metaborate 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.

Two acute oral toxicity studies were conduced on sodium metaborate dihydrate in rats. The mortality results from the two studies gave a non-monotonic response, 0/5 male rats died at 1600 mg/kg, 2/5 died at 2000 mg/kg and 1/5 died at 2500 mg/kg. Probit analysis produced a LD50 value of 3251 mg/kg, however the value lay outside the range of experimental doses. Using the dose interval of 1.25, the next higher dose level would expected to be 3125 mg/kg, assuming that one rat would die, the LD50 could be computed to be 7660 mg/kg assuming that complete mortality at 3125 mg/kg the value obtained by extrapolation is 2436 mg/kg. Therefore the acute median lethal oral dose of sodium metaborate dihydrate falls in the range of 2.4 to > 7.5 mg/kg (Denton 1995, 1996).

The following acute oral data were obtained:

No acute oral studies of sodium pentaborates have been conducted. Studies were conducted on an analogue substance

Sodium metaborate (tetrahydrate): 2330 mg(183 mg B)/kg

The following acute inhalation data were obtained:

No acute inhalation studies of sodium pentaborates 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 sodium pentaborates have been conducted. Studies were conducted on an analogue substance

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

Disodium Tetraborate Decahydrate: >2000 mg/kg bw (226 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, disodium tetraborate decahydrate, disodium tetraborate pentahydrate, boric oxide and disodium octaborate tetrahydrate will predominantly exist as undissociated boric acid. At about pH 10 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 un-dissociated boric acid. Since other borates dissociate to form boric acid in aqueous solutions, they too can be considered to exist as un-dissociated 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

Sodium pentaborate is not classified for the oral, dermal or inhalation routes, as the LD50 values of analogue substances exceed the limit for classification. No acute oral, inhalation or dermal toxicity studies with sodium pentaborate were available, however theLD50 values for the dermal and inhalation routes for the disodium tetraborates exceed the limit for classification.