Barium oxide, obtained by calcining witherite

Endpoint summary

Description of key information

acute oral toxicity study similar to OECD 401 (Tardiff et al. 1980): LD50 = 132 mg /kg bw (test substance BaCl2)

Additional information

According to Regulation (EC) 1907/2006 (REACH), acute toxicity testing does not need to be conducted if the substance is classified as corrosive to the skin (column 2 adaptation, annex VII). Based on the corrosive properties of barium oxide as demonstrated by a Corrositex® assay (OECD Guideline 435, BASF SE 2015), the test substance is classified as corrosive to the skin, category 1B (H314) according to Regulation (EC) 1272/2008 (CLP). Thus, acute toxicity testing with BaO is not required.

Hydrolysis of BaO to Ba(OH)₂ and subsequent dissociation can result in the release of Ba²⁺ ions. In order to account for potential Barium toxicity, data obtained with barium chloride (BaCl₂), a well soluble barium salt (for details please refer to the weight-of-evidence justification).

Animal data:

Borzelleca et al. administered 30, 100, and 300 mg/kg bw barium chloride solution by gavage and observed the animals for 24 hours. Mortality in the 300 mg/kg bw dose group was 70% in females and 80% in males, the lower dose levels did not show increased mortality. According to these data, the LD₅₀ for barium would be between 66 and 198 mg/kg bw (corresponding to 100 and 300 mg BaCl₂/kg, respectively). In accordance with this report, Tardiffet al. determined an LD₅₀ for Barium of 132 mg/kg bw (95% CL 112.2 -162.4) for adult rats. They administered 8 different doses to 10 animals/dose level group and observed them for 14 days following gavage. Calculation of barium content in BaO leads to a theoretical LD₅₀ of 147 mg BaO/kg bw for barium toxicity. Therefore, classification of BaO as acute toxic category 3 (H301) according to Regulation (EC) 1272/2008, Annex I, section 3.1 is warranted.

Human data:

Several reports of poisonings exist, mostly via ingestion, but also via dermal absorption through burns and inhalation. Due to a lack of exposure information as well as very divergent reactions of patients, the data are of only limited reliability. Nevertheless, they suggest that the dose is of eminent importance, as well as the route of exposure. A patient that inhaled BaCl₂experienced very rapid onset of severe intoxication symptoms, while other patients with oral ingestion had a later onset of disease. Further, the severity of symptoms showed great variation between subjects. In the literature, 3 -4 g of barium has been reported to be lethal (Handbook on the Toxicology of Metals, 1979). Since intestinal resorption has not been determined, it cannot be stated whether the case report data correlate with literature values.

Justification for classification or non-classification

BaO was shown to be corrosive in a Corrositex® assay and corrosive effects are very likely to be predominant upon acute exposure to barium oxide. Nevertheless, BaO can dissociate and form soluble Ba²⁺ ions upon contact with water.

Barium toxicity testing with barium chloride resulted in a LD₅₀ of 132 mg barium/kg bw/day, corresponding to 147 mg BaO/kg bw/day. According to Regulation (EC) 1272/2008 (CLP), BaO should be classified as acute toxic category 3 (H301).