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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Koc = 22909 and 7.943E6 (calculated)

Key value for chemical safety assessment

Additional information

According to Annex VIII of regulation EC No 1907/2006 the adsorptive properties should be evaluated. Therefore, the conduction of a study according to OECD 106 was intended. One of the qualifying statements listed in OECD method 106, claims that the test method is not applicable to substances which are not soluble in water to an extent which can be measured analytically. The water solubility of the test substance was determined to be < 0.05 mg/L. 0.05 mg/L represented the limit of quantitation for the analytical method. During the method development phase of this study, the concentration of the test substance was also determined to be < 0.05 mg/L in the 0.01 M calcium chloride buffer recommended in OECD Test Method 106. Since a method could not be developed to determine the exact water solubility of the test substance, the adsorption/desorption test was not performed.

Therefore, the adsorption coefficient was determined by calculations, based on estimations of the adsorption coefficient were performed using regression equations (Lyman, Reehl, Rosenblatt: Handbook of Chemical Property Estimation Methods. 1990) which relates the Koc with water solubility and with the n-octanol / water partition coefficient.

A logKoc of 4.36 based on water solubility and a log Koc of 6.90 based on the octanol-water-partition coefficient were determined.

Since the concentration used for the water solubility was a limit of quantitation and not the actual value for the test substance solubility, the calculated adsorption coefficient based on water solubility represents the lower limit for Koc.

 

To underline the results of the calculation above the QSAR program EpiSuite KOCWIN including 2 models was used to evaluate the Koc of the substance. As the substance includes several impurities the impurities with the highest fraction was chosen and declared as main impurity. For the substance itself (main compound) and this impurity (main impurity) the adsorptive potential was evaluated.

Based on the results of the QSAR calculations, main component and main impurity are estimated to have a high adsorptive potential.

 

Including the results of the adsorption/desorption calculation and the QSAR model the substance can be regarded to have a high adsorptive potential due to the calculated Koc values.According to McCall et al. (1981), substances with a Koc >5000 are classified as immobile in soils. Due to the calculated Koc values > 22909 it can clearly be assumed that this compound is immobile in soils.

 

In Article 13 of Regulation (EC) No 1907/2006, it is laid down that information on intrinsic properties of substances may be generated by means other than tests, provided that the conditions set out in Annex XI (of the same Regulation) are met. Furthermore according to Article 25 of the same Regulation testing on vertebrate animals shall be undertaken only as a last resort.

According to Annex XI of Regulation (EC) No 1907/2006 (Q)SAR results can be used if (1) the scientific validity of the (Q)SAR model has been established, (2) the substance falls within the applicability domain of the (Q)SAR model, (3) the results are adequate for the purpose of classification and labeling and/or risk assessment and (4) adequate and reliable documentation of the applied method is provided.

For the assessment of the substance (Q)SAR results were used for determination of adsorptive properties. The criteria listed in Annex XI of Regulation (EC) No 1907/2006 are considered to be adequately fulfilled and therefore the endpoint(s) sufficiently covered and suitable for risk assessment. Therefore, further experimental studies on adsorption/desorption are not provided.