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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The toxicity of the test substance to the freshwater alga Pseudokirchneriella subcapitata KORSHIKOV was determined in a study (BASF SE, 2016) according to the principles of OECD 201 (2006) under GLP conditions. The following effect concentrations were obtained after 72-h based on geometric mean measured concentration: The 72-hour ErC50 value was determined to be 5.25 mg test item/L. The 72-hour NOErC was determined to be 1.05 mg/L and the associated 72-hour ErC10 was determined to be 2.79 mg/L. All reported results refer to the geometric mean measured concentrations.

Key value for chemical safety assessment

EC50 for freshwater algae:
5.25 mg/L
EC10 or NOEC for freshwater algae:
2.79 mg/L

Additional information

The toxicity of the test substance to the freshwater alga Pseudokirchneriella subcapitata KORSHIKOV was determined in a study (BASF SE, 2016) according to the principles of OECD 201 (2006) under GLP conditions. The aim of the study was to assess the effects on growth rate and the effect on the development of biomass over a period of 72 hours. The study was conducted under static conditions. This study encompassed three replicates per test concentration, two replicates for the blank control and two replicates for the positive control. A WAF was prepared. The test solutions were prepared by directly adding of test substance to the test medium and stirring for about one day until visibly dissolved. Small particles and marbles were visible on the bottom of the stock solutions after stirring. Undissolved test substance was removed by filtration with a membrane filter (pore size 0.2μm). The exposure was started after separation of the undissolved material by adding inoculum culture at a ratio of 1:100. The test solution after addition of algal inoculum was considered equivalent to the nominal concentration since no more than 1 % dilution occurs. The cell density of the inoculum culture in exponential growth phase is determined and then adjusted to 30000 cells/mL with OECD media so that a 1:10 dilution of inoculum will result in an initial cell density of 3000 cells/mL in the test replicates. The initial inoculum biomass was reduced in this test due to the closed test vessels. The cell density was reduced in order to limit the binding of the test substance to the growing algal biomass. The nominal concentration of the test substance were 0 (control), 1.25, 2.5, 5, 10, 20 mg/L and the measured concentrations of the test substance were determined to be 1.05, 2.15, 4.27, 8.44 and 16.2 mg/L. Sampling was performed at the start of the exposure (0 h) from the inoculated replicate of each concentration and the control. At the end of the exposure (72 h) samples were taken from the combined inoculated (+algae) replicates of the test concentrations and of the combined inoculated control group. The samples were analyzed via HPLC. A reference substance potassium dichromate was used as positive control. The ErC50 after 72 hours of the control substance potassium dichromate was determined to be 1.03 mg/L. These results indicate that the algae are responding normally to toxicant stress. All measured concentrations of the test substance in the test water deviated less than 20 % from the geometric mean measured concentrations. Thus, the test substance was stable in solution under test conditions and the geometric mean measured concentrations are an accurate representation of exposure levels maintained throughout the test period. Nevertheless and following recommendations in OECD 201 the results are evaluated based on the geometric mean measured concentrations. The 72-hour ErC50 value was determined to be 5.25 mg test item/L. The 72-hour NOErC was determined to be 1.05 mg/L and the associated 72-hour ErC10 was determined to be 2.79 mg/L.