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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The toxicity of Cyclacet towards Desmodesmus subspicatus was investigated according to OECD guideline 201 under GLP. Algal cells were exposed to nominal concentrations of 1.0, 3.2, 10, 32 and 100 mg/l and observed for 72 hours. The 72h-EC50 and 72h-NOEC (both based on growth rate) were found to be 25 and 3.2 mg/l, respectively, based on nominal concentrations and6.4 and 2.0 mg/L, based on the geometric mean, respectively. Analysis of the test preparations at 0 hours showed measured test concentrations to range from 101% to 109% of nominal. A decline in measured test concentrations was observed at 72 hours in the range of 3% to 19% of nominal. This decline was considered to be due to both slight instability of the test item in culture medium as was observed in the preliminary stability analyses conducted and also adsorption of the test item to the algal cells present. In addition, the toxicity decreases over the time period 0 -72 hours and therefore initial measured concentrations can be used, which result in EC50 and EC10 of 25 and 11 mg/l, respectively, using growth rate. To be conservative the EC50 and EC10 values were determined using geometric mean concentrations resulting in 6.4 and 2.0 mg/l, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
6.4 mg/L
EC10 or NOEC for freshwater algae:
2 mg/L

Additional information