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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The 48-h ErC50 and 48-h ErC10 of Rosamusk are 3.8 mg/L and 1.1 mg/L respectively, based on a read across from CP Formate, which was tested in a study in accordance with OECD TG 201 with an obtained 48-h EC50 and 48-h ErC10 of 7.1 and 1.5 mg/L . Rosamusk toxicity to algae is converted from the CP Formate EC50 and EC10 values based on the difference between the measured log Kow values of 4.9 and 4, respectively, and the MW of 196 and 184 g/mol, respectively.

Key value for chemical safety assessment

EC50 for freshwater algae:
3.8 mg/L
EC10 or NOEC for freshwater algae:
1.1 mg/L

Additional information

No experimental data is available for Rosamusk, therefore read-across is performed to the close structural analogue CP Formate. The read across justification is presented in the Aquatic Endpoint summary, the read across document is also attached there.

CP Formate's algae toxicity

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.

Rosamusk's algae toxicity

Rosamusk has a higher log Kow and a slightly lower water solubility, compared to CP Formate (log Kow is 4.9 and 4.0 and water solubility is 12.6 and 26.1 mg/L, respectively), which can be expected from the additional methyl group in Rosamusk. In view of the difference in log Kow > 0.5 this needs to be accounted for. First the conversion from mg/L to Mmol is needed, which then need to be log transformed because the toxicity is related to the log Kow and not to Kow. The calculation equation is: (Log (x ug/l source / mol weight source)) *(log Kow target / Log Kow source) *( 10^)*mol weight target = ug/l target. Conversion from ug/l to mg/l divide the value with 1000. The 48-h ErC50 and 48-h ErC10 of Rosamusk are 3.8 and1.1 mg/L derived from a read across from CP Formate, based on the difference between the measured log Kow values of 4.9 and 4, respectively, and the MW of 196 and 184 g/mol, respectively.

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