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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The effect of the test item on the growth of Pseudokirchneriella subcapita was investigated according to OECD Guideline 201. The following results were determined based on the geometric mean measured test concentrations: 72 and 96 hour  EC50 (mg/L) for growth rate was > 0.077 mg/L, the 72 hour and 96 hour NOEC based on growth rate was determined to be 0.070 mg/L and 0.031 mg/L, respectively, and the LOEC was 0.077 mg/L at 72 hours and 0.070 mg/L at 96 hours.

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Additional information

A study was performed to assess the effect of the test item on the growth of the green alga Pseudokirchneriella subcapitata. The method followed that described in the OECD Guidelines for Testing of Chemicals (2006) No 201, "Freshwater Alga and Cyanobacteria, Growth Inhibition Test" referenced as Method C.3 of Commission Regulation (EC) No 761/2009 and the US EPA Draft Ecological Effects Test Guideline OPPTS 850.5400.

Pseudokirchneriella subcapitata was exposed to solutions of the test item at concentrations of 6.25, 12.5, 25, 50 and 100% v/v saturated solution (three replicate flasks per concentration) for 96 hours, under constant illumination and shaking at a temperature of 24 ± 1 °C. Chemical analysis of the test preparations at 0 hours showed measured test concentrations to range from less than the limit of quantitation (LOQ) of the analytical method employed, which was determined to be 0.011 mg/L, to 1.1 mg/L. A decline in measured test concentration was observed at 24 hours in the range of less than the LOQ to 0.32 mg/L. At 48, 72 and 96 hours a decline to less than the LOQ was observed for all test concentrations. Given this decline in measured test concentrations it was considered appropriate to calculate the results based on the geometric mean measured test concentrations.

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results based on the geometric mean measured test concentrations: 72 and 96 hour EC50 (mg/L) for growth rate was > 0.077 mg/L, the 72 hour and 96 hour NOEC based on growth rate was determined to be 0.070 mg/L and 0.031 mg/L, respectively, and the LOEC was 0.077 mg/L at 72 hours and 0.070 mg/L at 96 hours.

The decline in test item within relatively brief periods means that a stable concentration was not attained. Therefore the test should not be regarded reliable without restriction. The repeated observation of virtually complete disappearance suggests that this reflects an inherent property of the test item, although the cause of this is currently unknown.

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