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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The influence of the test substance on the growth of the freshwater algae Pseudokirchneriella subcapitata KORSHIKOV was assessed in a static dose response test according to OECD 201 (2006). The 72-hour ErC50 was determined to be 0.805 mg test item/L, the 72-hour NOErC was determined to be 0.351 mg test item/L and the associated 72-hour EC10 was determined to be 0.435 mg test item/L. All values were based on geometric mean measured concentrations.

Key value for chemical safety assessment

EC50 for freshwater algae:
0.805 mg/L
EC10 or NOEC for freshwater algae:
0.435 mg/L

Additional information

The toxicity of the test substance to the freshwater alga Pseudokirchneriella subcapitata KORSHIKOV was determined according to the principles of OECD 201 (2006) and the Commission Regulation (EC) No 761/2009/C3 (2009) under GLP conditions. The aim of the study was to assess the effects on growth rate and yield over a period of 72 hours. The study was conducted under static conditions. This study encompassed 6 treatment groups (5 dose rates of the test item, control) with three replicates per test concentration and six replicates for the control. At test start 100 mL of the test concentrations were inoculated with 5000 algal cells per mL test medium and defined volumes of the algal suspensions were sampled after 0, 24, 48 and 72 hours for determination of cell densities by spectrophotometrical measurement. The samples of the test media sampled at the start and at the end of the test after 72 hours of exposure were analyzed via capillary gas chromatography - mass spectrometry (GC-MS). The nominal test concentrations of 0.46, 1.0, 2.2, 4.6, 10 mg test item/L and a control are corresponding to geometric mean measured concentrations of 0.35, 0.82, 1.80, 3.62, 8.45 mg test item/L and control (0 mg test item/L). The measured concentrations of the test substance in the test water were in a range of 74 - 84 % of the nominal concentration at start of exposure. After 72 hours, the measured concentrations remained within ± 20 % of the initially measured concentration in test groups > 1 mg/L. In the lower test groups, > 20 % of the test substance was lost in the algae inoculated samples. The decrease at the end of exposure was most likely due to binding (adsorption) of the test substance to the growing algal biomass in the lower concentrations. To evaluate adsorption to algae, additional samples were analyzed from the uninoculated replicate 0 of each test group and the control at the end of the exposure (72 h). All uninoculated replicates were within ± 20 % of the initially measured concentrations. OECD 201 states that the alga growth inhibition test is a more dynamic test system than most other short term aquatic toxicity tests. Disappearance of the test substance from solution by adsorption to the increasing algal biomass does not mean that it is lost from the test system. Consequently, the results demonstrate the consistency of test substance concentrations over the defined exposure period and the geometric mean measured concentrations calculated using the uninoculated replicates were used to evaluate the results.

The following effect concentrations (mg/L) were obtained after 72-h based on nominal concentration: The 72-hour ErC50 value was determined to be 0.99 mg test item/L and the 72-hour EyC50 was determined to be 0.629 mg test item/L. The 72-hour NOErC and the 72-hour NOEyC were determined to be 0.46 mg/L and greater than 0.46 mg test item/L, respectively and the associated 72- hour LOErC and LOEyC were determined to be 1 and 0.46 mg/L, respectively.

The following effect concentrations (mg/L) were obtained after 72-h based on geometric mean measured concentration: The 72-hour ErC50 value was determined to be 0.805 mg test item/L and the 72-hour EyC50 was determined to be 0.494 mg test item/L. The 72-hour NOErC and the 72-hour NOEyC were determined to be 0.351 mg/L and greater than 0.351 mg test item/L, respectively and the associated 72- hour LOErC and LOEyC were determined to be 0.82 and 0.351 mg/L, respectively.