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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

The 72h-EC50 for cell growth inhibition and growth rate reduction based on TWA concentrations were both determined to be >0.017 mg/L i.e. exceeded the maximum soluble concentration of test substance in test medium at a loading rate of 100 mg/L. The NOEC for both the parameters was considered at 0.017 mg/L (TWA concentrations).

Key value for chemical safety assessment

EC50 for freshwater algae:
0.017 mg/L
EC10 or NOEC for freshwater algae:
0.017 mg/L

Additional information

A study was conducted to determine the toxicity of the test substance to algae and cyanobacteria according to OECD Guideline 201 and EU Method C.3, in compliance with GLP. A combined limit/range-finding test (test type: static) was performed, during which, six replicates of exponentially growing algal cultures (Pseudokirchneriella subcapitata) were exposed to a control and to a WAF prepared at a loading rate of 100 mg/L. In addition, three replicates per group were exposed to WAFs prepared at 1.0 and 10 mg/L. The initial algal cell density was 10E04 cells/mL and the total exposure period was 72 h. The test concentrations were analytically verified and the pH, temperature, cell density and appearance were recorded throughout the study. At the start of the test, the actual test concentrations were 0.044 and 0.101 mg/L in the WAF prepared at 100 mg/L and incubated with and without algae, respectively. At the end of the exposure period, the measured concentrations had dropped to 21-23% of the initial concentrations. Based on these results, the Time Weighted Average (TWA) concentrations were calculated and used to determine the effect parameters. The TWA concentrations were estimated to be 0.017 and 0.039 mg/L in samples with and without algae, respectively. No significant differences were recorded between the values for growth rate or yield at any of the test concentrations when compared to the control group. Microscopic observations at the end of the test revealed a normal and healthy appearance of the algal cells exposed to the highest test concentration when compared to the control. The study met the acceptability criteria prescribed by the study plan and was considered valid. Under the study conditions, no significant differences were recorded between the values for growth rate or yield for Pseudokirchneriella subcapitata at any of the test concentrations. Both the EC50 for growth rate inhibition (72h-ERC50) and the yield inhibition (72hEYC50) were beyond the range tested (EC50: >0.017 mg/L), i.e. exceeded the maximum soluble concentration of test substance in test medium at a loading rate of 100 mg/L. The 72h-NOEC for both growth rate inhibition and yield inhibition was 0.017 mg/L (TWA concentration corresponding to a loading rate of 100 mg/L) (Augusiak, 2017).