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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The test item was found to inhibit the growth of the freshwater green alga Pseudokirchneriella subcapitata after 72 hours with the following effect values (geometric mean measured concentrations). The EC50 values with 95% confidence intervals for inhibition of specific growth rate (ErC50) and yield (EyC50) after 72 hours were 42.7  (23.6 - 62.4 mg/L) mg test item/L and 0.0575 (0.0343 - 0.332) mg test item/L, respectively. The ErC20 and NOEC values for inhibition of specific growth were 1.45 (0.246 - 8.22) and 0.0241 mg test item/L, respectively, and the EyrC20 and  NOEC values for yield were <0.0143 mg test item/L. The most reliable values are considered to be 72h-ErC50 growth rate = 42.7 (23.6 – 62.4) mg/L and ErC20 growth rate = 1.45 (0.246 – 8.22) mg/L.    

Key value for chemical safety assessment

EC50 for freshwater algae:
42.7 mg/L
EC10 or NOEC for freshwater algae:
1.45 mg/L

Additional information

The toxicity of the test item to the unicellular freshwater green alga Pseudokirchneriella subcapitata was determined according to the principles of OECD guideline 201 and GLP. 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 with an initial cell density of 5297 cells/mL. Seven nominal concentrations were tested in a geometrical series : 0.316 - 1 - 3.16 - 10 - 31.6 - 100 - 316 mg/L corresponding to the geometric mean measured concentrations of 0.0143 - 0.0241 0.0262 - 0.343 - 0.355 - 75.5 - 331 mg/L after 72 hours. Three replicates were tested for the test item concentrations and six replicates for the control.

Environmental conditions were determined to be within the acceptable limits. The test item concentrations were analysed at all concentration levels at test start (0 hour) after 24 hours, after 48 hours and at the end of the test, via LC-MS/MS analysis. The measured concentrations at the start of exposure (0h) were in the range of 91 to 119% of the nominal values, after 24h <LOQ to 119%, after 48h <LOQ to 110% and at the end of exposure (72h) <LOQ to 105%. The disappearance of the tested substance is inversely proportional to the increase of the tested concentrations. The assessment of the curves of inhibition in function of the tested concentrations indicates that the decrease in concentration of the substance in the course of the test is accompanied by a decrease in growth inhibition.

The EC50 values with 95% confidence intervals for inhibition of specific growth rate (ErC50) and yield (EyC50) after 72 hours were 42.7 (23.6 - 62.4) mg test item/L and 0.0575 (0.0343 - 0.332) mg test item/L, respectively. The ErC20, ErC10 and NOEC values for inhibition of specific growth were 1.45 (0.246 -8.22), <0.355 and 0.0241 mg test item/L, respectively, and the ErC20, EyC10 and  NOEC values for yield were <0.0143 mg test item/L.

In the study, all the validity criteria are fulfilled according to the OECD Guideline 201. Since the validity criteria are fulfilled for the growth rates in the controls, the results of the inhibition of the test item on the growth rate are prefered to the results obtained on the yield. Moreover in the study, it is considered that the geometric mean values of the NOEC/LOEC and EC10 represent artificial decay curves and should be considered with utmost caution. The ErC50 and the ErC20 calculated by sigmoidal dose-reponse regression with a confidence intervals are more reliable than the NOEC/LOEC and ErC10. The EC50 values with 95% confidence intervals for inhibition of specific growth rate (ErC50) and yield (EyC50) after 72 hours were 42.7 (23.6 - 62.4 mg/L) mg test item/L and 0.0575 (0.0343 - 0.332) mg test item/L, respectively.