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Toxicity to aquatic algae and cyanobacteria

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From the EU RAR, most of the algal toxicity data have been generated with potassium dichromate. Where comparison is possible, the toxicity of sodium chromate or sodium dichromate, when expressed on a total chromium basis, does not appear to be significantly different from that of potassium dichromate. 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.

The available EC50 values for algae range from 0.13 to 4.6 mg/l Cr; NOEC values are in the range 0.01 to 0.64 mg/l Cr. With marine algae, salinity and sulphate ion concentration have been shown to be important factors in determining the toxicity of chromium (VI). The toxicity of chromium (VI) is generally highest at low salinities (<2‰) and low sulphate ion concentrations (Riedel, 1984 and 1985; Frey et al., 1983). At higher salinities, marine alga appears to be of similar or slightly lower sensitivity as freshwater algae.