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Toxicity to aquatic algae and cyanobacteria

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Description of key information

The substance is acutely not toxic to algae up to the maximum water solubility.

Key value for chemical safety assessment

Additional information

In a GLP guideline study following OECD Guideline 201 green algae (Desmodesmus subspicatus) were exposed for 72 hours to a saturated solution of tris-2 -ethylhexylamine. This is a limit test with a nominal concentration of 100 mg/L. the algal biomass was determined by measuring the fluorescence of the treatments and the control. The correlation between algal biomass and fluorescence was determined via counting of the cell number in a dilution series of an algal suspension (Desmodesmus subspicatus). The calibration curve has a high correlation coefficient of R² = 0.9957, which proves the good correlation of cell number and fluorescence.

The test solutions were prepared following general guidance provided in OECD 23 in order to generate a saturated solution of the test substance in test medium. Undissolved test material was not removed. Hence, the algae were exposed to the total load of the test substance. The dissolution behavior was observed during exposure in uninoculated test assays. The control assays were clear and did not show any turbidity. At the start of exposure (0 h), the test substance was homogeneously dispersed in water showing a slight turbidity. After 24 h, 48 h, and 72 h, undissolved test substance was observed in the water surface as oily drops in addition to the previous observation.

An analytical method by LC/MS for the determination of the test substance was developed at the Analytical Chemistry Laboratory of Experimental Toxicology and Ecology of BASF SE, Ludwigshafen, Germany. However, an analytical verification of the test material concentration is not feasible as the limit of quantitation (LOQ) is significantly higher than the water solubility of the Substance. The LOQ for this method was approx. 0.3 mg/L and the water solubility of the test substance is < 0.002 mg/L. No reliable method for analyses in the required concentration range could be developed.

Therefore, concentration control analysis was not performed. However, since all reasonable efforts were taken to produce a saturated solution of the test substance in test media, following the guidance in OECD 23, the test results should be based on loading concentration. The daphnids were exposed to the entire loaded mass of test substance over each renewal period.

A study on the stability of the substance in this algal growth inhibition test was also not performed due to the lack of a reliable analytical method. With regard to the stability a decline in the concentration could be possible by adsorption based on the high log Kow. However, the substance is not biodegradable and is not expected to degrade by hydrolysis. As undissolved test material was not removed from the test solution, the dissolved concentration of the Substance should still remain stable as the undissolved test material could have served as a reservoir to compensate for any losses.

Overall, no adverse effects on the test organisms were observed. Based on nominal concentrations, the 72-h ErC50 for effects on algae growth rate is > 100 mg/L (nominal (loading), BASF SE, 2010).

Therefore, it can be concluded that the substance is acutely not harmful to algae up to the maximum water solubility.

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