Registration Dossier

Administrative data

Description of key information

Zinc tetraoxychromate is a sparingly water soluble chromate. A valid test on acute inhalation toxicity of another sparingly water soluble chromate, strontium chromate, exists and is utilised for read-across. In acute oral toxicity, a poorly described study on strontium chromate is notified but the LD50 is based on read-across from slightly water soluble calcium chromate. There is no non-human information on acute dermal toxicity of zinc tetraoxychromate. Human information on zinc tetraoxychromate is also lacking.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Dose descriptor:
LD50
327 mg/kg bw

Acute toxicity: via inhalation route

Endpoint conclusion
Dose descriptor:
LC50
770 mg/m³

Acute toxicity: via dermal route

Endpoint conclusion

Additional information

According to REACH guidelines, two toxicity tests are required (oral and inhalation or dermal acute toxicity tests) for showing acute toxicity of a substance. Based on the assumptions made in the toxicokinetics of the bioavailability, exposure via inhalation route is relevant for chromates. As zinc tetraoxychromate is a sparingly water soluble chromate, read-across from other sparingly water soluble chromates as strontium chromate is the priority when regarding the acute toxicity of zinc tetraoxychromate. In a well-performed acute inhalation toxicity test with strontium chromate (product Strontium Chromate L203E, purity 97%), the LC50was between 0.27 and 0.51 mg/l air (corresponding ca. 0.069 and 0.13 mg/l of Cr(VI)), suggesting category 2 in classification. There are two other studies on acute toxicity of strontium chromate. In these, the substance was orally or intratracheally administered in rats, giving a LD50value of 3,118 mg/kg bw (795 mg Cr/kg) and 16.6 mg/kg (4.2 mg Cr/kg), respectively. According to this acute oral toxicity study and read-across approach from strontium chromate, there would not be classification for zinc tetraoxychromate. There is no non-human information on acute dermal toxicity of zinc tetraoxychromate. Human information on zinc tetraoxychromate is also lacking.

Data with highly water soluble chromates exist, but this data can be regarded as a worst case scenario. This is because both the well-documented inhalation study (LC500.27-0.51 mg/l) and the supporting oral toxicity study (LD503,118 mg/kg bw) with strontium chromate give evidence on the lower acute toxicity also for zinc tetraoxychromate compared to the results received in studies with highly water soluble hexavalent chromium compounds (e.g., in Gad et al. 1986: LC50for acute inhalation toxicity 0.094-0.158 mg/l, and LD50for acute oral toxicity 51.1-57.2 mg/kg bw).

If read-across was used directly from strontium chromate to zinc tetraoxychromate for the classification for acute inhalation toxicity, the classification into category 2 would be justified. However, neither strontium or zinc are known to be acutely toxic, and thus the acute toxicity depends on the Cr(VI) content of the substance. Based on the molecular weights, the LC50values obtained with strontium chromate (0.27-0.51 mg/l air) correspond to 0.069-0.13 mg/l of Cr(VI). These Cr(VI) concentrations correspond to LC50values of 0.77-1.45 mg/l of zinc tetraoxychromate, based on the molecular weights. Finally, these LC50values justify the classification of zinc tetraoxychromate as category 3 for acute inhalation.

Furthermore, it is reasonable to judge acute oral toxicity of zinc tetraoxychromate to category 4 as a study with slightly soluble calcium chromate suggests. This is milder classification than with highly water soluble chromates but tighter than in the poorly described study with strontium chromate.

Justification for classification or non-classification

Conclusion: Zinc tetraoxychromate is classified for acute oral toxicity as 'harmful if swallowed' (category 4), and for acute inhalation toxicity 'toxic if inhaled' (category 3). No further testing is suggested.