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Long-term toxicity to aquatic invertebrates

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Description of key information

A key NOEC value was calculated as the geometric mean of two experimental NOEC values and a valid and verified QSAR calculation using ECOSAR available for the substance.

Key value for chemical safety assessment

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

Additional information

Two studies are available investigating the long-term toxicity of N,N-dimethyldecanamide (CAS 14433-76-2) to aquatic invertebrates. However, both studies are regarded as valid but on its own not adequately reflecting the long-term toxicity of the substance. Therefore, the results of both studies as well as results of QSAR calculations are combined in a Weight of Evidence (WoE) in accordance to the REACh Regulation (EC) No 1907/2006, Annex XI General rules for adaptation of the standard testing regime set out in Annexes VII to X, 1.2, to cover the data requirements of Regulation (EC) No. 1907/2007 Annex IX and X (ECHA, 2012c).

 

The first study was conducted according to GLP and OECD guideline 211 using Daphnia magna as test organism (BASF 2013). Nominal test substance concentrations of 0.01, 0.032, 0.1, 0.32 and 1 mg/L were tested under semi-static conditions. The test substance was dissolved in water using ultrasonic bath, a magnetic stirrer and folded filters. Young female Daphnia, aged less than 24 h, were used. After 21 days of exposure, the total number of offspring/parent animal alive was assessed.

Effective concentrations were 98.1 to 112.5% in freshly prepared median and <60.7 - 91.5% in media after 48 or 72 hours of exposure. Thus, the results are expressed as time-weighted means of measured concentrations, since nominal test substance concentrations could not be maintained throughout the test. The 21-day NOEC regarding reproduction is determined to be 0.079 mg/L, while the NOEC regarding mortality is determined to be >= 0.866 mg/L.

 

The second study was also conducted according to GLP and OECD guideline 211 using Daphnia magna as test organism (Gyimesi et al. 2013). Nominal test substance concentrations of 0.03, 0.09, 0.27, 0.81 and 2.43 mg/L were tested under semi-static conditions. Like in the first study, the test substance concentrations could not be maintained during the test. Thus, the results of this test were also expressed as time-weighted means of measured concentrations. The 21-day NOEC regarding growth and reproduction is determined to be 0.37 mg/L.

 

The considerable variability in the determined effect concentrations although obtained from very similar test systems and tested concentrations assumes that the results are biased by the method used to calculate the effect concentration.

 

Therefore, a QSAR calculation using ECOSAR v1.00 was used to verify the test results and to improve the data situation in order to determine a reliable NOEC value to be used for PNEC derivation. The suitability and accuracy of results obtained from ECOSAR v1.00 was validated by comparison of experimental data and ECOSAR estimations for a structurally very similar substance (CAS 67359-57-3 = 1:1 mixture of the C8- and the C10-homologue). The measured 21-d EC10 value of 1.3 mg/L fits very well to the ECOSAR calculation of 1.2 mg/L (based on the baseline toxicity model) indicating the suitability of using the QSAR results for prediction of chronic toxicity to aquatic invertebrates. Thereby, the neutral organic SAR is considered to more accurately predict the chronic toxicity compared to the amide based model since the calculated short-term toxicity of 5-10 mg/L based on the neutral organic SAR (baseline toxicity) fits much better to the measured effect values.

 

In conclusion, the NOEC values obtained in the two available tests and the valid QSAR calculation of 0.76 mg/L can be considered to equally contribute to the determination of a reliable NOEC value for the long-term toxicity of the test substance to aquatic invertebrates. Thus, in a WoA approach a key NOEC value was calculated as the geometric mean of all three NOEC values, resulting in a NOEC of 0.28 mg/L.