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Short-term toxicity to fish

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Based on a review of existing fish data from the EU RAR, an acceptable assessment of acute toxicity was achieved.

The acute toxicity of chromium (VI) to fish appears to be dependent on the water hardness and also pH. Higher toxicity has generally been seen in soft water and at more acidic pHs, particularly those <6.5. This dependence appears to follow a similar pattern to the uptake of chromium (VI) by fish (see Section 3.1.1.2.4), where it has been postulated that at lower pHs, the main form of chromium (VI) in solution is the monovalent HCrO4 - ion, which has been postulated as having a higher mobility across cell membranes than the divalent chromium (VI) oxyanions found at higher pH.

For some fish species, toxicity data are available for more than one of the chromium (VI) compounds included in this assessment. The available information indicates that, when expressed on a total chromium concentration, there are no significant differences between the toxicity of sodium chromate, sodium dichromate and potassium dichromate (allowing for differences in water properties). This is as would be expected if the equilibria between the chromate and dichromate anions are established in the test medium. Little information is available for ammonium dichromate and chromic acid, but it would be expected that their toxicity would be similar to that of the other chromates/dichromates, when expressed on a total chromium concentration basis.