Bis(dimethylamino)methylvinylsilane

Toxicity to aquatic algae and cyanobacteria

Description of key information

The toxicity of the test item toDesmodesmus subspicatuswas determined according to OECD 201 resp. EU C.3.

Two experiments were performed. In the 1st experiment one of the validity criteria was not met (Coefficient of variation of average growth rate in the control replicates during the whole test period was slightly above 7 %). Therefore, the experiment was repeated. The results of the 1st experiment (with exception of the results of the measurement of the accuracy values in buffered algal medium) are not stated in the report, but will be kept together with the other raw data in the GLP archive of the test facility.

The study was performed using 5 concentrations ranging from 1 to 100 mg/L (nominal). Incubation time (test systemDesmodesmus subspicatus) was 72 hours. The cell concentration of each replicate was determined by measuring the cell numbers every 24 ± 1 hours with an electronic particle counter. Growth rate µ and the yield were determined from the cell number at the respective observation times.

Significant inhibition of algal growth was observed at the nominal concentrations 10, 32 and 100 mg/L. In the lowest tested nominal concentration (1 mg/L), unexpected inhibition of algal growth was observed. Inhibition of algal growth in this treatment was not caused by toxicity of the test item because at the beginning of the test, only a very low test item con-centration of 1 mg/L was measured and at the end of the test no more test item was detectable. The second lowest concentration 3.2 mg/L showed a stimulation of algal growth in spite of a higher measured test item concentration. In the higher tested concentrations, a clear dose-response relationship was observed. Therefore, the lowest concentration was excluded from the evaluation of the results.

At the 10 mg/L concentration, the second replicate was also not included in the evaluation. Here, the cell number was much lower than in the other two replicates and also much lower than the cell numbers in the next higher concentration 32 mg/L.

If this replicate were to be included in the statistical evaluation, the result for the endpoint growth rate would result in an implausible high value for the NOEC.

The NOEC does not provide direct information on the level of inhibition observed. The NOEC only indicates whether an observed inhibition compared to the control must be evaluated as significant by a statistical hypothesis test.

Due to the high variation of the cell numbers in the three test replicates, no variance homogeneity was found in the evaluation. This is the reason why, despite the low cell number and the associated clear inhibition of values, no significant difference was found between the concentration 10 mg/L and the control with the chosen hypothesis test. In this case the NOEC would be determined as 10 mg/L.

In the statistical evaluation without the second replicate at the concentration 10 mg/L, variance-homogeneity requirements are fulfilled and the NOEC was determined as 3.2 mg/L which can be stated as plausible.

As the test item is hydrolyzed in aqueous medium fast, the hydrolysis product Dimethylamine DMA was analyzed in this study in accordance to OECD guidance series on testing and assessments No. 23. At the start and at the end of the test, the content of DMA in the test solutions was determined using a LC/MS/MS- method.

The measured concentrations for the nominal concentrations 3.2 – 100 mg/L lay between 94 % and 103 % of the nominal concentrations at the beginning of the test and between 100 % and 113 % of the nominal concentrations at the end of the test. Only in the lowest concentration 1 mg/L (not used for evaluation of biological results), no test item could be detected.at the end of the test

Therefore, the determination of the biological results was based on the nominal concentration.

The EC50-values for inhibition of the algal growth rate (ErC50) and yield (EyC50) after 72 hours were 39.83 mg/L (CI 33.28 – 47.75) and 10.63 mg/L (CI 8.5 – 13.27) mg/L, respectively. The NOEC-values for inhibition of growth rate and yield after 72 hours were 3.2 mg/L. The results of the test can be considered valid.

Key value for chemical safety assessment

EC50 for freshwater algae:

39.83 mg/L

EC10 or NOEC for freshwater algae:

3.2 mg/L

Additional information

The EC50-values for inhibition of the algal growth rate (ErC50) and yield (EyC50) after 72 hours were 39.83 mg/L (CI 33.28 – 47.75) and 10.63 mg/L (CI 8.5 – 13.27) mg/L, respectively. The NOEC-values for inhibition of growth rate and yield after 72 hours were 3.2 mg/L. The results of the test can be considered valid.