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Long-term toxicity to aquatic invertebrates

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Description of key information

Key study performed according to GLP and Guidelines (OECD 211, OPPTS 850.1300)
The chronic toxicity of the test item to the freshwater invertebrate Daphnia magna has been investigated.
Mean measured concentrations of test substance were substantially lower than nominal concentrations.
21-day NOEC (measured) = 0.121 mg/L
21-day NOEC (nominal) = 1.0 mg/L

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:
0.121 mg/L

Additional information

The chronic toxicity of 9-decenoic acid methyl ester to Daphnia magna was evaluated under flow-through conditions in a guideline study (OECD 211; OPPTS 850.1300) conducted in accordance with Good Laboratory Practices. 

No significant concentration-dependent adverse biological effects were observed for any concentration for any endpoint: adult mortality, reproduction, or growth (length and weight).

 

Based on nominal concentrations, the 21-day NOEC was 1.0 mg a.i./L. However, measured concentrations were not within 20% of the nominal concentrations, so mean measured concentrations in the replicate solutions are reported. Based on mean measured concentrations, the 21-day NOEC and LOEC were 0.121 and >0.121 mg a.i./L, respectively based on all parameters. No meaningful 21-day EC50 can be calculated because no adverse effects were observed.

 

The flow-through conditions did not resolve the problem with rapid disappearance of test material as seen in previous short-term tests. Diluter stock solutions were prepared using dimethylformamide as a solvent. Concentrations in the diluter stock solution was close to expected. Flow rates were maximized (six volume additions to each test chamber in a 24-hour period). Functioning of the diluter system was confirmed with saline solution. Flow-through operation was initiated 4 days before test initiation to pre-treat test chambers.

 

The mean measured concentrations in test chambers were only 5 to 21% of nominal. Nominal and (measured) concentrations (in mg a.i./L) were: 0.065 (0.00638), 0.13 (0.0162), 0.25 (0.0266), 0.5 (0.0428) and 1.0 (0.121). Loss of test substance was observed even in the initial mixing chamber, with concentrations being 31 to 56% of nominal. The large gap between nominal and measured concentrations makes interpretation of the test results problematic.

 

The maximum acceptable toxicant concentration could not be defined due to low water solubility and rapid disappearance of the test substance.

 

Based on the apparent instability of the test material and this decline/disappearance during the test, it is considered that the test should not be regarded reliable without restriction. Due to this, the results from this study have not been used to further refine PNEC’s or to further review the environmental classification of the substance.

 

Efforts to achieve stable test substance concentrations are underway. At present, factors such as volatilization, photodegradation, hydrolysis and biodegradation do not appear to control the inherent property of the test substance to leave the water column. Sorption to surfaces, silicone adhesive and organic material do appear to have a role. The results of any repeated testing that achieves stability of the test material in water will be compared to this study and the existing short-term study to refine PNECs and environmental classification as appropriate.