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Toxicity to aquatic algae and cyanobacteria

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Description of key information

96 h ErC10 22 µg/L based on growth rate, Selenastrum capricornutum, initial measured (Springborn Laboratories 1990f).

96 h ErC50 >22 µg/l based growth rate, Selenastrum capricornutum, initial measured (Springborn Laboratories 1990f).

Key value for chemical safety assessment

Additional information

A 96-hour ErC50 of >22 µg/L and ErC10 of 22 µg/L have been determined for the effects of the test substance on growth rate of Selenastrum capricornutum (new name: Pseudokirchneriella subcapitata).

A 96-hour EC50 of >22 µg/l and NOEC of <22 µg/l have also been determined for the effects of the test substance on cell density of Selenastrum capricornutum (new name: Pseudokirchneriella subcapitata). The results are expressed relative to a measured initial concentration of the substance. Measured concentration in samples showed a decline over time (to <1 µg/l after 48 h in one replicate; to <1 µg/l in two replicates and to 3.3 µg/l in the third, by the end of the test).

In accordance with ECHA guidance, R.7b, 2016, results for algal growth rate should be used to determine effect concentrations. A re-analysis of the results was conducted, revealing an inhibition of the average specific growth rate in the treatment group by 6.8% and 6.4% after 72 h and 96 h, respectively, when compared to the control. Therefore, the ErC10 is 22 µg/L, which is the maximum water solubility level in the test medium.

It is noted that the validity of this test has been called into question by previous reviewers because of sub-standard growth in the closed system control culture. A parallel open system control grew adequately and met the validity criteria and whilst effects associated with the closed system may have contributed, the cell density effects of this study are accepted as a realistic worst case for algae.

The reliability of two other test results reporting EC50 in excess of the limit of solubility could not be determined.