1,4-dioxacycloheptadecane-5,17-dione

Toxicity to aquatic algae and cyanobacteria

Description of key information

Weight of Evidence approach; geometric means between the two results (experimental and QSAR results):
- EC50 = 3.39 mg/L
- EC10/NOEC = 2.10 mg/L

Key value for chemical safety assessment

EC50 for freshwater algae:

3.39 mg/L

EC10 or NOEC for freshwater algae:

2.1 mg/L

Additional information

Due to the total loss of substance observed in the experimental study (EU Method C.3 with GLP statement) and the poor quality of the description of the analytical method, the algae study is considered as weak and it was preferred to use a weight of evidence approach with a QSAR (ECOSAR) estimation to provide a more robust assessment of the toxicity of the substance to algae.

In the algae toxicity study, performed according to EU Method C3 with GLP statement, the cultures of Desmodesmus subspicatus were exposed to the substance at nominal concentrations of 2.0, 2.8, 4.0, 5.6, 8.0, 11.3, 16.0 mg/L under static conditions. Due to the total loss of this relatively low volatile substance (<LOQ) observed at the end of this study and the uncertainty as to the reason for this, the endpoint values were recalculated with ToxRat Professional v2.10 using the initial measured concentrations. The recalculated 72h-ErC10 and 72h-ErC50 values were determined to be 10.35 mg/L (95% CL: 10.29 - 10.40 mg/L) and 14.58 mg/L (95% CL: 14.54 - 14.62 mg/L), respectively.

In addition, toxicity to green algae was estimated using the ECOSAR v1.11 QSAR model available from the U.S. EPA. The estimation 96h-EC50 was 0.788 mg/L and the estimated NOEC was 0.426 mg/L (esters class), calculated from a measured log Kow value (4.3) and linear regressions.

The substance falls within the applicability domain and therefore the predicted values can be considered reliable.

To obtain more reliable acute and chronic toxicity values, geometric means between these two results were determined. The EC50 and EC10/NOEC values were determined to be 3.39 mg/L and 2.10 mg/L, respectively.

Further investigation is ongoing on this difficult substance in order to determine whether instability or analytical issues account for the rapid loss observed under ecotoxicological test conditions.