Reaction mass of Amines, coco alkyl and β-Alanine, N-(2-carboxyethyl)-, N-coco alkyl derivs. and β-Alanine, N-coco alkyl derivs.

Partition coefficient

Description of key information

A weighted average logKow of 2.51 is recommended.

Key value for chemical safety assessment

Log Kow (Log Pow):

2.51

at the temperature of:

20 °C

Additional information

Harlan report 41202685 sets out the results of a slow-stirring experiment, presented as octanol/water partition coefficients for individual components (‘peaks’).  The report does not identify individual peaks, but does present log Kow values for all major peaks (with one exception). The report contains information that would allow quantitation of the individual peaks in the complete material, with the caveat that the mass spectroscopic quantitation of the individual peaks was based on selected ion monitoring. The report does present individual component concentrations in the separate phases in mg/L, although these appear to represent ion counts normalized to overall material concentration, rather than reflecting concentrations (mass/volume) of the individual components. Together with pertinent information on phase amounts, it is possible to use the information in this report to derive a weighted average log Kow value for the entire material.

A weighted average log Kow for a multicomponent substance may be defined as e.g. proposed in the hydrocarbon block method referred to in Ch R.11: PBT assessment of the Guidance on information requirements and chemical safety assessment.

The approach described by Verbruggen et al., 1996 represents a mole fraction weighted average logKow as an overall hydrophobicity parameter for a mixture.

For the test substance, mole fractions of individual components are not available.  However, given the fact that the material has a known alkyl chain length distribution characterized by 45% C₁₂, 30% C₁₄, and 15% C₁₆, and a reaction product distribution characterized by 45% ß-Alanine, N-(2-carboxyethyl)-, N-coco alkyl derivatives, 26% ß-Alanine, N-coco alkyl derivatives, and 29% cocoalkylamines, the range in molecular masses is small enough that using weight fractions^[1]rather than mole fractions will not result in a significant bias.

Harlan report 41202685 describes a slow stirring experiment that was conducted in triplicate, where for each vessel from this triplicate, samples were taken at 5 consecutive time points, in order to establish whether a distribution equilibrium was reached. Partition coefficients were calculated for all time points. Establishment of equilibrium was judged based on partition coefficient vs. time profiles; however, while partition coefficients showed little (i.e. no significant) dependence on time, concentrations in both the organic and aqueous phase did show a (significant) time dependence. Since absolute amounts, not ratios, are relevant here, only measurements at equilibrium time points, rather than averages over all time points (as was done for the derivation of log Kow values in the Harlan report) were used. More specifically, the reported peak areas in the individual phases at the latest time points that appeared valid were used (some components tended to disappear towards the end of the experiment, and some components were not quantifiable at some or all (peak 4) time points). Since measured values for specific time points were applied, log Kow values calculated for these same time points, rather than overall averages, as presented in the Harlan report, were also used.

Reported peak areas in the aqueous and organic phase were multiplied by the reported analysis dilution factors (10⁵for the organic phase and 10⁴for the aqueous phase - 3\10⁴for peaks 1 and 2), and the resulting amounts summed over both phases and then converted to percentages to derive a relative abundance (‘weight fraction’) for each component (‘peak’). A weighted average log Kow was then calculated by multiplying the log Kow values of the individual peaks by the weight fraction of the peaks and summing the result. For sake of comparison, this was also done for the log Kow values reported in the Harlan report. The results table shows that the difference in weighted log Kow is minimal. The information reported in the Harlan report does not allow calculation of a mass balance to determine what fraction of the material is not accounted for by this approach – however, a qualitative evaluation of the chromatograms (specifically those on pages 15 and 16) suggests that the relative abundances calculated as described above are in agreement with these chromatograms.

 

peak	Relative abundance	logKow (our selection)	logKow (Harlan)
1	20.49%	0.447	0.487
2	10.07%	1.65	1.68
3	33.86%	3.27	2.97
4
5	16.53%	3.3	3.27
6	7.13%	3.4	3.33
7	3.44%	3.31	3.52
8	1.46%	3.19	3.18
9	3.55%	3.08	3.17
10	1.39%	1.6	1.95
11	2.10%	3.02	3.08
Weighted log KOW		2.51	2.42

 

Based on the information available therefore, a weighted average log Kow of 2.51 can be assigned to the test substance, as analyzed according to Harlan Laboratories report no. 41202685.

Footnotes

[1] Using weight fractions gives results that are comparable to using mole fractions based on an average molecular weight.

References

Verhaar, H.J.M., van Loon, W.M.G.M., Busser, F.J.M., Smit, E., and Hermens, J.L.M. (1994). Development of Parameters for Evaluating the Effects of Mixtures of Organic Micropollutants on the Environment.

Verbruggen, E.M.J., van Loon, W.M.G.M., and Hermens, J.L.M. (1996). A hydrophobicity parameter for complex organic mixtures. Environmental Science and Pollution Research 3. pp. 163-168.