Reaction Mass of (1R)-1-[(1S)-3,3-dimethylcyclohexyl]ethyl formate and (1R,2S)-2,6,6-trimethylcycloheptyl formate

Toxicity to aquatic algae and cyanobacteria

Description of key information

An OECD TG 201 guideline study in compliance with GLP with freshwater algae (Desmodesmus subspicatus) is available for the test substance. Algae were exposed to nominal concentrations of 1.0 and 3.2 mg/L and WAFs prepared at loading rates of 10, 32 and 100 mg/L under static conditions for 72 hours. Because the test material is volatile, testing was conducted in airtight closed test vessels in order to minimise possible losses due to volatilisation. At the start of the test, the actual test concentrations were 0.81, 2.3, 7.7, 23 and 35 mg/L for the concentrations prepared at 1.0, 3.2, 10, 32 and 100 mg/L, respectively. The measured concentrations decreased to 10-17% of initial after 24 hours and further to 1.7-5.5% of initial after 48 hours of exposure. Based on these results, the Time Weighted Average (TWA) exposure concentrations were calculated. The TWA concentrations corresponded with 0.19, 0.49, 1.4, 4.5 and 7.1 mg/L, respectively.

Reduction of growth rate gradually increased with increasing TWA concentration from 1.4% at the lowest to 43% at the highest concentration. Statistically significant reduction of growth rate was found at test concentrations of 0.49 mg/L and higher. Inhibition of yield increased with increasing TWA concentration of the test substance from 0.19 mg/L upwards resulting in 83% inhibition at a TWA concentration of 7.1 mg/L. Statistically significant inhibition of yield was found at TWA concentrations of 0.49 mg/L and higher. Microscopic observations at the end of the test revealed a normal and healthy appearance of the exposed cells when compared to the control. Based on these data, the 48 -h EC50 values for growth and yield were determined to be >7.1 mg/L and 2.0 (95% C.L: 0.86 -4.8 mg/L), respectively. The 48-h ErC10 and EyC10 values were determined at 1.5 mg/L and 0.27 mg/L, respectively. The 48-h NOEC finally, is 0.19 mg/L for both endpoints. The validity criteria were not met in this study as the pH in various solutions during both the combined limit/range-finding and the final test increased with more than 1.5 units and above 9.0 at the end of the test. The increase was due to the volatility of the test substance and the consequence of testing in a closed system. Despite the addition of extra NaHCO3 and the adjustment of the pH of the test medium before the study it proved not possible to maintain the pH. However, algal growth met the criterion of at least a 16-fold increase. Altogether, the study integrity considered to be not adversely affected by the deviation.

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:

1.5 mg/L