Hydrogen bromide

Endpoint summary

Description of key information

Hydrogen bromide (HBr) is an inorganic gas under standard temperature and pressures and forms a strong mineral acid (hydrobromic acid) in water.  HBr and hydrobromic acid are classified/labelled with the symbols "C" and "Xi" and the risk phrases "R35" and "R37". 
Though there are minimal animal repeated dose data on hydrogen bromide (HBr) available there are sufficient data available on the analogue substances hydrogen chloride (HCl)  and phosphorus tribromide which hydrolyses to phosphonic acid and HBr. (Read-across justifications in Section 8.6 Repeat dose toxicity)
In an oral administration test, the LD50 value for hydrogen chloride has been determined to be 238-277 mg/kg bw for female rats (OECD SIDS 2002)
Stavert, D.M., et al. (1991) indicated the toxic effects of hydrogen bromide were comparable to those of hydrogen chloride and hydrogen fluoride on the respiratory system at a high concentration of exposure (1300 ppm).
 
There is a reported inhalation LC50 valueof 2860 ppm (9464.55 mg/m3) in rats (Back, K.C., et al., 1972). In a 4-hour nose only exposure to the analogue substance PBr3, female rats gave an LC100 at ca. 4 mg/L. The report summarised in Wolfe, R.E., et al. (1997) also noted that corrosion and local irritation effects were observed in the low dose of 1.48 mg/L. Stavert, D.M., et al. (1991) indicated that the effects of hydrogen bromide were comparable to hydrogen chloride and hydrogen floride and the threshold concentrations for hydrogen bromide vapours are about three times higher than bromine

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion

Dose descriptor:

LD50

Value:

238 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion

Dose descriptor:

LC50

Value:

9 464.55 mg/m³ air

Additional information

Hydrogen bromide (HBr) is an inorganic gas under standard temperature and pressures and forms a strong mineral acid (hydrobromic acid) in water. HBr and hydrobromic acid are classified/labelled with the symbols “C” and “Xi” and the risk phrases “R35” and “R37”. In addition, the pH of hydrobromic acid (the strong mineral acid formed by HBr in water) is known to be acidic – the pH of a 62 % solution is 1. Though there are minimal animal repeated dose data on hydrogen bromide (HBr) available there are sufficient data available on the analogue substances hydrogen chloride (HCl) and phosphorus tribromide which hydrolyses to phosphonic acid and HBr. (Read-across justifications in Section 8.6 Repeat dose toxicity.) Acute inhalation studies in animals have been submitted (Annex VIII Section 8.5.2) in support of the existing classification on the substance and the analogue substance PBr₃. Supporting data from acute oral toxicity studies on the analogue substance hydrogen chloride (HCl) have been submitted supporting the corrosive effect of this group of acidsviathe oral route.

 

Oral

In an oral administration test, the LD₅₀ value for HCl has been determined to be 238-277 mg/kg bw for female rats (OECD SIDS 2002).

 

Inhalation

In a 4-hour exposure to PBr₃ vapours in nose-only exposure chambers, Wolfe, R.E., et al. (1997) reported mortality (100 % died or were euthanized moribund on day 1) was seen in female rats exposed to approximately 4 mg/L (equivalent to 3.664 mg/L). No mortality was seen in groups of male rats exposed under the same circumstances to analyzed concentrations of 1.48 mg/L and below. Pathology seen in the high-dose animals and in those of the 1.48 mg/L group were corrosion or severe irritation of the upper respiratory tract.

Stavert, D.M., et al. (1991) indicated the toxic effects of HBr were comparable to those of HCl and hydrogen fluoride (HF) on the respiratory system at a high concentration of exposure (1300 ppm). Major effects in the nasal passages were related to necrohemorrhagic rhinitis. Mouth breathing animals had fibronecrotic tracheitis of variable severity.

Back, K.C.,et al. (1972) reported the 60-minute LC₅₀ of HBr in rats is 2860 ppm (9464.55 mg/m³) rats. The comparable LC₅₀ in mice was 815 ppm. Ivanov, I.G., et al. (1976) conducted a parallel acute inhalation toxicity experiment to one using bromine, testing HBr at sublethal concentrations in a four hour exposure. Based on observations of decreased respiratory rate compared to control, decreased “olfactory acuity” for the aromatic thymol, and an increase in free-lying cells in the lungs, the concentration deemed the LIMir was 26 mg/m³. The concentration that also caused acute effects (LIM ac) based on changes in the summation threshold index (STI) in the nervous system and body temperature was 66 mg/m³. Thus, the LIMir for HBr is 2 1/2 times lower than the LIMac, which is evidence of the specificity of irritant effect. The comparable LIM for bromine was 10 mg/m³, meaning the threshold concentrations for HBr vapours are about three times higher than bromine.

 

Other routes

HBr given by the intraperitoneal route to rats, produced lethality in 50 % of the animals (LD₅₀) at a dose of 76 mg/kg. (RTECS, 1986).

Justification for classification or non-classification

HBr is an inorganic gas under standard temperature and pressures and forms a strong mineral acid (hydrobromic acid) in water. HBr and hydrobromic acid are classified/labelled with the symbols “C” and “Xi” and the risk phrases “R35” and “R37”. In addition, the pH of hydrobromic acid (the strong mineral acid formed by hydrogen bromide in water) is known to be acidic – the pH of a 62% solution is 1. Acute inhalation studies in animals have been submitted (Annex VIII Section 8.5.2) in support of the existing classification on the substance and the analogue substance PBr₃. Supporting data from acute oral toxicity studies on the analogue substance HCl have been submitted supporting the corrosive effect of this group of acids via the oral route.