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Ecotoxicological information

Toxicity to microorganisms

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The rate and extent to which chromium (III) oxide produces soluble (bio)available ionic and other chromium-bearing species in environmental media is limited. Further, the poor solubility of chromium (III) oxide is expected to determine its behaviour and fate in the environment, and subsequently its potential for ecotoxicity. Proprietary studies are not available for chromium (III) oxide. However, the fate and toxicity of chromium (III) oxide in the environment is evaluated by assessing the fate of its ecotoxicologically relevant moiety, the chromium (III) ion, and read-across to data available for other chromium (III) substances is applied.

In accordance with ECHA’s Guidance on IR & CSA, Appendix R.7.13-2 (2008),the poorly soluble substance chromium (III) oxide is evaluated by comparing the dissolved chromium (III) ion level resulting from the T/Dp at a loading rate of 1 mg/L after 7 d with the lowest effect concentration as determined for the (soluble) chromium (III) ion. For the (soluble) chromium (III) ion, no inhibition of respiration of activated sludge was observed in a GLP guideline study withpotassium chromium sulphate dodecahydrate and a 3 h ≥ NOEC > 1000 mg Cr/L was derived (Caspers, 1988). In single species tests, the lowest effect concentration determined for the (soluble) chromium (III) ion is a NOEC of 0.26 mg Cr/L observed for the soil bacteriumAzobactervinelandii (Ueda et al., 1988). Dissolved chromium concentrations of <0.01 µg/L in the T/Dp after 7 days at pH 6 (i.e. the pH that maximizes the dissolution) are significantly lower than the lowest effect concentration derived in activated sludge respiration inhibition tests (i.e. NOEC ≥ 1000 mg Cr(III)/L) as well as the lowest effect concentration derived in single species tests (NOEC of 0.26 mg Cr/L). Hence, chromium (III) oxide is not sufficiently soluble in environmental media to inhibit activated sludge respiration or cause toxicity to microorganisms at the level of the lowest effect concentration (expressed as the NOEC).

For further information on the applied read-across approach and the evaluation of the poorly soluble substance chromium (III) oxide, please refer to the section "Cr2O3_Aquatic toxicity".

Based on the poor solubility of chromium (III) oxide in environmental media, inhibition of activated sludge respiration or toxicity to microorganisms is not expected.

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