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Toxicity to aquatic algae and cyanobacteria

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Description of key information

GLP study performed according to OECD 201 guideline:  72h-ErC50 of 0.214 mg/L and 72h-ErC10 of 0.109 mg/L (initial measured concentrations, growth rate inhibition)

Key value for chemical safety assessment

EC50 for freshwater algae:
0.214 mg/L
EC10 or NOEC for freshwater algae:
0.109 mg/L

Additional information

Two studies were performed according to OECD Guideline 201 with GLP statement. The growth inhibition of the freshwater algal Pseudokirchneriella subcapitata exposed to OO-t-BUTYL-O-(2-ETHYLHEXYL)MONOPEROXYCARBONATE was determined for a duration of 72h.

In the first study (Gancet, 2005), algae were exposed to concentrations varying from 0.6 to 30 mg/L (nominal).

Effective concentrations have been calculated using initial measured concentrations of the test item which were determined by gas chromatography coupled with mass spectrometry. The 72h-ErC50 and 72h-ErC10 were evaluated at 0.766 mg/L and 0.353 mg/L, respectively. All the validity criteria of the test guideline have been fulfilled.

Nevertheless, as no details are available on the test solution preparation method (i.e. phase separation; whether droplets of undissolved test substance may have been incorporated into the test solutions), the study has been quoted Klimish 2 and it has been decided to perform a new algae toxicity test in 2013 in order to confirm or not these results.

In this second study (Gancet, 2013), algae were exposed to 0.1 to 5 mg/L (nominal concentrations) of test substance. The test item concentration was not maintained throughout the duration of these algae tests. The loss of test substance in the test medium could be related to adsorption to the increasing algal biomass or to hydrolysis in aqueous media. Therefore, it was decided to express the effective concentrations as initial measured concentrations which were determined by HPLC/MS/MS. The 72h-ErC50 and 72h-ErC10 based on growth rate were evaluated at 0.214 mg/L and 0.109 mg/L respectively. All the validity criteria of the test guideline have been fulfilled.

Both algae toxicity tests showed ErC50 and ErC10 < 1 mg/L. It was decided to use the results of Gancet, 2013 study which were more detailed in the study report and gave the lowest effective concentrations.