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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The log Koc value was predicted with the program KOCWIN and with three QSPR methods. The log Koc = 3.196 indicates that the substance has low mobility in soil and sediment according to the classification scheme of McCall et al. (1981).

Key value for chemical safety assessment

Koc at 20 °C:
1 570.3

Additional information

Discussion of results

As no single computational model could be identified which would fit completely to this task, the Koc of menthyl acetate eventually was being calculated from the geometric mean of the data generated by four individual QSPR approaches.The five different ways of QSPR computations were based on the experimentally derived log Kow of the test item of 4.0.

Method

Log KOC

PCKOCWIN log KOW

3.072

Gerstl method

3.379

Sabljic and Güsten (esters)

3.01

Sabljic and Güsten (mainly hydrophobic)

3.34

Geometric mean

3.196

The resulting geometric mean of log Koc = 3.196 (Koc = 1570 L/kg) is considered as valid as it is being supported by several different QSPR approaches. It is proposed to use the predicted value for the adsorption coefficient of log Koc = 3.196 in the chemical safety assessment.

The substance is considered to have "low mobility" in sediments and soil (McCall 1981).

Waiving of further adsorption/desorption studies

It is being proposed to waive further studies on adsorption/desorption, as it basically would be requested by REACH Annex IX. According to ECHA guidance documents a strong justification needs to be provided for avoiding experimental confirmation of the computed Koc data, as basically being requested by REACH Annex IX. The justification arguments for supporting the robustness of this QSPR-derived Koc result reads as follows: 1. For final computation four individual Koc values were being used which were all based on the log Kow of menthyl acetate; the relatively high log Kow of menthyl acetate of 4.0 is considered to have significant impact on Koc computation. 2. The Koc computations of the four methods all are based on real physical properties 3. The four individual Koc data points represent a coherent data set without outliers 4. The log Koc of menthyl acetate resulting from the geometric mean of these four values therefore is being supported by four different QSPR models Furthermore, concerning data interpretation of the resulting Koc of menthyl acetate, the predicted adsorption coefficients uniformly are pointing in one direction and clearly indicate that the substance has to be considered as having low mobility in sediments and soil. For these reasons additional adsorption/desorption testing cannot be expected to reveal new results with any added value concerning the risk assessment of this substance, thus additional Annex IX studies on adsorption/desorption shall be waived.

[LogKoc: 3.196]