N,N-dimethyldecylamine N-oxide

Adsorption / desorption

Description of key information

The Koc was estimated using KOCWIN v2.00, although surfactants fall outside the applicability domain of the model. The Koc value  derived was 24.3 L/kg. This value is lower than an experimentally derived Koc for C12-14 AO. For the CSA it was concluded that read across to the experimentally derived value of Koc from the C12-14 study was appropriate. In this study adsorption of C12-14 amine oxide in three soil types was determined according to OECD TG 106. Kom values were obtained for C12 and C14 homologues, converted to Koc and these values were used to calculate Kd values normalised to 2 % organic carbon. The geometric mean of the Kd values was used to calculate the Koc for C12-14 amine oxide of 1525 L/kg.

Key value for chemical safety assessment

Koc at 20 °C:

1 525

Additional information

The Koc has been estimated using KOCWIN v2.00. This gave a Koc value of 24.3 L/kg. It should be noted that surfactants fall outside the applicability domain of the model and the reliability of the derived value cannot be assessed. The value is lower than the experimentally derived Koc for C12 -14 AO described below. For the CSA it was concluded that read across to the Koc value resulting from this study was appropriate as a reasonable worse case.

The adsorption of C12-14 amine oxide in three soil types was determined in a GLP study according to OECD TG 106 [Van de Ruit (2002)]. The soil types used were obtained from various locations in the Netherlands. Organic matter/clay contents of the three soils (labelled 545070, 543151 and 545347) were 2.7 %/3.2 %, 0.8 %/11 % and 2.6 %/24 % respectively.Two homologues (C12 and C14) of the test material were evaluated for adsorption in the study (desorption was not tested). The applied soil : solution ratio was 1:5. For all three soil types, adsorption equilibrium was reached at 7 h of incubation. Adsorption percentages were in the range of 68 - 100% after this time.

The recovery of the duplicate soiless control solutions was 109 and 110 % for the C12-homologue and 109% (2x) for the C14 homologue at equilibrium (7 hrs), indicating no adsorption onto the container occurred. No matrix effect of the soil onto analytical results was observed for the measurement of test material in aqueous phase after equilibration of 0.01 M CaCI2 solution in Suprapur® water with soil number 545347. Results of the blanks were therefore not taken into account when calculating the results for the test substance. The influence of soil on the pH of the aqueous phase was in the range of approximately 0.2 to 1.3 pH unit.

The mean adsorption coefficient (Kd) for soil 5545070, soil 543151, and soil 545347 was 8.3, >16.9 (56.1), and >16.1 (18.3) L/kg, respectively for the C12 homologue and >16.8 (24.5), >15.8 (17.2) and >16.8 (33.3) for the C14 homologue. The mean adsorption coefficient related to the soil organic matter (Kom), for soil 5545070, soil 543151, and soil 545347 was 307, >2113 (7013), and >619 (702) L/Kg, respectively for the C12 homologue and >622 (906), >1969 (2151) and >646 (1281) for the C14 homologue.

In order to calculate the Koc value for use in the exposure assessment, Kom values were converted into Koc values using the relationship soil organic matter = 1.724 x soil organic carbon content. The Kom value for the C12 homologue in soil 543151 was excluded from calculations as a suspected outlier due to the low percentage organic carbon of the soil type used, which may limit correlation with organic carbon content, and since the data failed to correlate with the increased affinity for soils anticipated to be demonstrated by the C14 homologue. The Koc values were then used to calculate the theoretical distribution coefficient Kd normalised to 2% organic carbon. The geometric mean of the Kd values was calculated as 46.8 L/kg, equivalent to a Koc of 1525 L/kg.