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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Key study, OECD 201- GLP:

72h-NOEC = 1.2 mg/L

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
1.2 mg/L

Additional information

In an algal toxicity study performed in accordance with OECD guideline 201 and GLP, Pseudokirchneriella subcapitata (previous name: Selenastrum capricornutum) was exposed to the test item at mean measured concentrations of 0 (control culture medium), 0.15, 0.31, 0.63, 1.2, 2.5 and 5.1 mg a.i./L for 5 days under static conditions. Measurement of biomass and growth inhibition was done by determination of cell densities at approximately 24-hour intervals during the 5-day exposure period using an electronic particle counter.

The changes in mean cell density indicated that exponential growth occurred in the negative control replicates. Based on the cell density, the EC50 values on Days 1, 2, 3, 4 and 5 are 1.9, 2.7 (2.0-3.5), 1.3 (0.73-2.2), 2.8 (1.5-4.0) and 2.2 (1.6-2.7) mg a.i./L, respectively. Based on the growth rate, the ErC50 values on Days 1, 2, 3, 4 and 5 are 1.3 (0.47-2.6), 4.3, >5.1, >5.1 and >5.1 mg a.i./L, respectively. The No-Observed-Effect-Concentration (NOEC) values after 5 days were calculated to be 0.63 mg a.i./L, based on cell density, and 1.2 mg a.i./L, based on growth rate and area under the growth curve.

As the test was performed on 5 days, an analysis of raw data was performed using ToxRat v2.10 software to assess the toxicity of the substance at 72h: NOEC (72h) = 1.2 mg/L. ToxRat was not able to determine an EC50 at 72 hours.

Under the test conditions, the NOEC (72h) for the test item is greater than 1.2 mg a.i./L.