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Toxicity to aquatic algae and cyanobacteria

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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 thus evaluated by comparing the dissolved chromium (III) ion level resulting from the T/Dp at a loading rate of 1 mg/L after 7 and 28 d with the lowest acute or chronic effect concentration, respectively, as determined for the (soluble) chromium (III) ion.The lowest reliable acute and chronic effect concentrations determined for the (soluble) chromium (III) ion are a 72 h ErC50 > 148.1 microg Cr(III)/L and a 72 h ErC10 of 2 microg Cr(III)/L observed in a growth inhibition test for the effects of chromium (III) hydroxide sulphate on freshwater algae Desmodesmus subspicatus (Neuhahn, 2010). Dissolved chromium concentrations of <0.01 µg/L in the T/Dp after 7 and 28 days at pH 6 (i.e. the pH that maximizes the dissolution) are significantly lower than the lowest reliable acute effect concentration derived for algae (i.e. EC50 > 0.148.1 mg Cr(III)/L) and the lowest reliable chronic effect concentration derived for algae (i.e. ErC10 of 2.0 µg Cr(III)/L). Hence, chromium (III) oxide is not sufficiently soluble in environmental media to cause acute or chronic toxicity to algae at the level of the lowest acute and chronic effect concentration (expressed as the EC50/EC10, respectively).

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, toxicity to algae is not expected.

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