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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The growth inhibition test of the test substance with green algae was conducted with the test substance XDA according to OECD 201 and in compliance with GLP principles. The ErC50 (0 -72) and the ErC10 (0 -72) were calculated to be 31.5 mg XDA/L and 21.6 mg XDA/L, resp. These values correspond to ErC50 (0 -72) of 43.5 mg XDI/L and ErC10 (0 -72) of 29.8 XDI/L.

Key value for chemical safety assessment

EC50/LC50 for freshwater algae:
31.5 mg/L
EC10, LC10 or NOEC for freshwater algae:
21.6 mg/L

Additional information

Two toxicity studies to aquatic algae are available: one with XDI and one with the main transformation product XDA. Based on the rapid transformation of the parent material XDI to XDA, it was indeed deemed important to also evaluate the toxicity of the pure transformation product XDA.

The toxicity of XDI to green algae was tested in accordance with OECD guideline 201 and the principles of Good Laboratory Practice. Test solutions were prepared by adding XDI to test medium, and allowing the substance to dissociate completely.

The results were expressed as mean measured concentrations of the transformation product XDA (instead of nominal concentrations of XDI) and subsequently recalculated to the parent material XDI. So, the 72h- ErC50 and 72h-ErC10 were both > 23 mg XDA/L and > 31.7 mg XDI/L.

Both studies were reviewed and determined to be reliable. Although the XDA study received a lower Klimisch value due to a pH issue (pH partly out of the range advised by the test guidelines), it was judged that this issue did not influence the results of the study.

The results of both studies also were of the same magnitude.

Based on the fact that the results of the green algae study with XDA were bound values and the results with XDI unbound values (> values), it was decided to use the bound values of XDA as key value for this endpoint.

Key values for chemical safety assessment: 72h-EC50 for freshwater algae: 31.5 mg XDA/L; EC10 = 21.6 mg XDA/L

Key values for CLP classification: 72h-EC50 for freshwater algae: 43.5 mg XDI/L; EC10 = 29.8 mg XDI/L