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Endpoint summary

Description of key information

A number of sub-chronic and chronic studies on boric acid and disodium tetraborate decahydrate were carried out in rats, mice and dogs. In some cases these studies are research studies (Weir and Fisher, 1972; Dixon et al, 1976; Seal and Weeth, 1980; Lee et al., 1978; Treinen and Chapin, 1991; Ku et al., 1993), but most support that boron can cause adverse haematological effects and that the main target organ of boron toxicity is the testis.  The NOAEL for fertility effectsis equivalent to 17.5 mg B/kg bw/day that corresponds to NOAEL of 100 mg BA/kg bw (Weir, 1966a, b).

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Endpoint conclusion

Endpoint conclusion:

adverse effect observed

Dose descriptor:

NOAEL

100 mg/kg bw/day

Study duration:

chronic

Species:

rat

Quality of whole database:

The study meets generally accepted scientific standards with acceptable restrictions.

Repeated dose toxicity: inhalation - systemic effects

Endpoint conclusion

Endpoint conclusion:

no adverse effect observed

Dose descriptor:

NOAEC

103.9 mg/m³

Species:

rat

Quality of whole database:

The key study provides BMD which is based on results of two studies and therefore is more accurate and more precise than NOAEL established in one study. The oral BMD has been extrapolated to inhalation BMD of 103.9 mg/m³ for zinc borate anhydrous by route-to-route extrapolation (see section "DNEL derivation").

Repeated dose toxicity: inhalation - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - systemic effects

Endpoint conclusion

Endpoint conclusion:

no study available

Repeated dose toxicity: dermal - local effects

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

A number of studies on boric acid or disodium tetraborate decahydrate in diet or via drinking water for periods of 30 days to two years in rats, mice and dogs are available, however, the majority of these studies do not comply with current test guidelines, and they lack essential information regarding e.g. histological descriptions and statistical evaluations of the results. Most studies support that boron can cause adverse haematological effects and that the main target organ of boron toxicity is the testis. Other effects observed at high doses include rapid respiration, hunched position, bloody nasal discharge; urine stains on the abdomen, inflamed bleeding eyes, desquamation and swollen paws and tail, reduced food consumption and body weight gain. Treatment with boric acid and disodium tetraborate decahydrate disrupted spermiation, induced degeneration of testicular tubules and caused testicular atrophy. For effects on the blood system extramedullary haematopoiesis, reduced red cell volume and haemoglobin values and deposition of haemosiderin in spleen, liver and proximal tubules of the kidney were described. Several cases of anaemia have been observed in human poisoning cases. However, although doses in these poisoning cases are difficult to define, the effects occurred generally at relatively high concentrations.

Groups of albino rats and dogs were exposed to aerosols of boron oxide for periods up to 24 weeks, 6 hours a day for 5 days a week.The highest concentration rats were exposed was 470 mg/cu m for a period of 10 weeks. There were no significant changes in tissues from rats or in chemical analyses of rats and dogs blood. No changes or toxic signs were noted in the mature female dogs exposed for 23 weeks to a concentration of 57 mg/m³ (Wilding et al. 1959; 1960).

Boric acid, the main species present under physiological conditions, acts as a Lewis acid and as such owns the ability to complex with hydroxyl, amino and thiol groups from diverse biomolecules, like e.g. carbohydrates and proteins (BfR, 2006). Such a mechanism could be involved in effects of boron on different enzyme activities (Huel et al., 2004).

A NOAEL for effects on testes and the blood system of 17.5 mg B/kg bw/day can be derived (with a LOAEL of 58.5 mg B/kg bwday) from two 2-year studies in rats on boric acid and disodium tetraborate decahydrate (Weir, 1966a,b).

Justification for selection of repeated dose toxicity via oral route - systemic effects endpoint:  The study with the longest duration and the lowest NOAEL was chosen (key study).  Justification for selection of repeated dose toxicity inhalation - systemic effects endpoint:  No study is selected since BMD of 10.3 mg B/kg bw, established in an oral developmental study in rats (Allen et al., 1996) is more appropriate for derivation of inhalation DNEL (by route-to-route extrapolation) than NOAEC for boron oxide established in a 90-day inhalation study (Wilding et al., 1960).  Repeated dose toxicity: via oral route - systemic effects (target organ) urogenital: testes

Justification for classification or non-classification

Boric acid is classified under the 1st ATP to CLP as Repr. 1B; H360FD.