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Long-term toxicity to fish

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Description of key information

A long-term fish toxicity test can be calculated reliably using the critical body burden approach. This results in a NOEC of 0.21 mg/l.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater fish:
0.21 mg/L

Additional information

The NOEC calculation method is based on the critical body burden (CBB) approach and is presented in ECHA's R.16 Appendix 7.8. The used equation for long-term fish toxicity is CBB = NOEC x BCF. The CBB for narcotic type of chemicals is 0.1-1 mMol. Cashmeran can be considered a narcotic chemical despite the substance containing an alpha,beta-unsaturated bond. The double bond between the two rings of Cashmeran (the vinyl-group) has no potential leaving H-groups. On both sides C-atoms are connected to this bond and these C’s are belonging to ring structures. Therefore there is no site of attack for enzymes at this vinyl-site as is also presented by Schultz et al. 2005, discussing alpha,beta-unsaturated bonds. This double bond within these two ring structures is therefore unreactive. Also the ketone bond is unreactive, because of the ring that sterically hinders the reactivity this ketone bond. This can also be seen in e.g. the liver metabolism profiler of the OECD Toolbox where this vinyl and/ketone group remain intact (see IUCLID section 7.1 on toxico-kinetics). In addition, the acute aquatic toxicity has been calculated using the lethal body burden (LBB) approach (LBB=LC50 x BCF). The LBB is 1.6 mMol when using the LC50 fish of 2.12 mg/L and the measured BCF of 157 (and molecular weight of 206). This LBB value shows that for the chronic fish calculation the CBB of 0.16 mMol can be used. The long-term fish NOEC thus becomes: 0.21 mg/l (0.16 mMol x MW of 206 = NOEC x 157 (BCF).

In view of the reasoning above the uncertainty of the prediction is limited and is also in line with the predicted NOEC value of the long-term QSAR on narcotics for fish which is 0.2 mg/l (using the measured log Kow of 4.2 and EpiSuite as the model). As presented above, the MoA of Cashmeran is via a neutral organic pathway because of the saturated vinyl-bond and the sterically hindered ketone bond.

Schultz, T.W., Netzeva, T.I., Robert, D.W., and Cronin, M.T.D., 2005, Structure-Toxicity Relationships for the effect to Tetrahymena pyriformis of aliphatic carbonyl-containing, alpha,beta-unsaturated chemicals, Chem. Res. Toxicol., 18, 330 -341.