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Toxicity to aquatic algae and cyanobacteria

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In a 72 h toxicity study conducted according to OECD guideline 201, freshwater algae (Pseudokirchneriella subcapitata) were exposed to Sodium ferrocyanide under static conditions. The EC50 for growth rate reduction (72h-ErC50) was 3.1 mg/L (95% confidence interval ranging from 0.77 to 12 mg/L) based on average exposure concentrations. The 72h-NOEC for growth rate reduction was 0.05 mg/L. The study is considered to be reliable with restrictions based on the non-biological effects seen in the test system and the decrease of Fe concentrations throughout the test period, one can be doubtful to which substance the algae are actually being exposed to. 

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In a 72 h toxicity study conducted according to OECD guideline 201, freshwater algae (Pseudokirchneriella subcapitata) were exposed to Sodium ferrocyanide under static conditions at the following nominal concentrations: 0 (blank-control), 0.10, 0.32, 1.0, 3.2, 10 and 32 mg/L. The EC50 for growth rate reduction (72h-ErC50) was 3.1 mg/L (95% confidence interval ranging from 0.77 to 12 mg/L) based on average exposure concentrations. The 72h-NOEC for growth rate reduction was 0.05 mg/L. The study is considered to be reliable with restrictions. The reliability of the study is lower as there are non-biological effects (i.e. coloration, precipitation in the test medium) seen in the test system which cannot be fully explained and are not observed in the fish and daphnia tests. The test system of the algae study seems to induce specific conditions which might influence the stability of the ferrocyanide complex (e.g. test medium composition and light intensity). The analytical method used was based on Fe (recalculation of the Fe measurements to test substance was performed to obtain the average exposure concentrations) and it was shown to have a large margin of error for the lower test concentrations. Based on the fact that both the NOEC and EC50 were in the lower concentration range, the accuracy of these values is not high. However, based on the procedural recovery on March 4th 2013 of <83% at a nominal concentration of 0.1 mg/L, one can view the results as an underestimation of toxicity and thus the NOEC and EC50 can be viewed as worst case approach values for toxicity. Based on the non-biological effects seen in the test system and the decrease of Fe concentrations throughout the test period, one can be doubtful to which substance the algae are being exposed to. In addition, a supporting publication was available, but this did not contain enough information on the test system, conditions and organisms. The results are therefore difficult to interpret.