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Description of key information

The Koc is required for exposure assessment and derivation of PNECsoil and PNEC sediment. The Koc for the oxygenated C10-C12 assessment entity has been derived from two main peaks in the HPLC determination of the UVCB substance. The mean log Koc for these two peaks is 2.45, which corresponds to a Koc of 282.

The determination was performed at 35°C (column temperature), however the values can be considered to represent the values at an unspecified, probably ambient temperature since no mention is made in the guidelines of the temperature at which the tabulated reference substances log Koc values were determined. Adsorption coefficients of the test and reference substances are assumed to vary with temperature in the same way.

Key value for chemical safety assessment

Koc at 20 °C:
282

Additional information

An OECD 121 HPLC test was conducted in order to determine the adsorption coefficient on soil and sewage sludge of Citrathal Concentrate S TW. The chromatograms showed seventeen peaks with more than 1% relative peak area, with adsorption coefficients that ranged from 1.2 to 4.5. Peaks with lower log Koc values are likely attributable to the oxygenated C10-C12 compounds present in the UVCB substance, since the presence of the alcohol, aldehyde and ether functional groups will promote aqueous solubility and mobility in soils. Since a single value is required for the exposure assessment and derivation of PNECsoil and PNEC sediment, the mean log Koc of the two largest peaks at the lower end of the chromatogram has been used (peak 3, 12.4%, log Koc = 2.4; peak 4, 11.0%, log Koc = 2.5) for this assessment entity.

The log Koc can be estimated from log Kow using the below regression model. A log Kow of 3.3 was assigned to the oxygenated C10-C12 assessment entity, which results in an estimated log Koc of 2.736, thus supporting the assignment of peaks 3 and 4 in the HLPC determination to this assessment entity and the use of the measured data for these two peaks.

Regression Model: Log Koc = 0.52 Log Kow + 1.02, n = 390, r2 = 0.63, s.e. = 0.56.

Applicability Domain: chemical class “Nonhydrophobics”, log Kow range of -2 to 8.0. All chemicals that are not classified as hydrophobics. Hydrophobics are chemicals with C, H, F, Cl, Br and I atoms. Since the C10-C12 oxygenated constituent group contains only C, H and O atoms it is considered “nonhydrophobic”.

Reference: ECG TGD on Risk Assessment, Part III, Chapter 4 (2003), available at https://echa.europa.eu/documents/10162/16960216/tgdpart3_2ed_en.pdf.

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