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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Adsorption to solid soil phase is not expected.

Key value for chemical safety assessment

Additional information

The adsorption of Triclosan to soil was tested in a study following OECD guideline 121. The adsorption coefficient Koc of Triclosan was assessed by determination of its retention time on a cyanopropyl HPLC column. A log koc of 2.92 (koc: 831.8) was determined (Ciba-Geigy 2006). In a study using water-suspended solids of a WWTP as medium a Koc of 47454 was detected (Ciba-Geigy, 1997).

The lower log Koc value was selected as key study since the study was performed according to an OECD method (OECD 121) with validation for several reference compounds which are chemically related to the test substance. In addition this study has a higher relevance for the evaluation of the adsorption potential for soils and sediments. The material derived from deactivated sewage sludge in the study by Ciba-Geigy (1997) is not representative for soils and sediments due to the very high organic carbon content, the composition in general and the texture of the material itself.

In a OECD guideline study (OCD 121), the adsorption coefficient for the metabolite Methyltriclosan was determined to be log Koc = 2.62. Therefore adsorption to solid soil phase is not expected.