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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Members of this category are expected to adsorb strongly to soils and sediment.

Key value for chemical safety assessment

Additional information

A measured Koc is not available for any member of this category. As the available measured log Kow are >3 the adsorption/desorption endpoint cannot be waived. However, ECHA's Guidance on Information Requirements and Chemical Safety Assessment R7a Endpoint Specific Guidance (2008) indicates that before commissioning a new study alternative sources of data (e.g. QSAR) on the adsorption/desorption potential of a chemical should used. If the calculated Koc proves to be influential in the risk assessment then it may be necessary to conduct a new study.

Soil sorption of non-ionic substances can be estimated from their log Kow. Several QSARs have been developed that calculate the Koc of non-polar hydrocarbons on the basis of their log Kow (e.g. Sabljic and Gusten, 1995). However, the category member with the lowest carbon number (and therefore expected lowest log Kow) has a calculated log Kow of 10.09 - 11.71 and therefore falls outside the applicability domains of these models (log Kow up to 7.5 for Sabljic and Gusten, 1995). There is a clear trend of increasing Koc with increasing log Kow for non-ionic substances. Therefore, a Koc has been calculated based on the highest log Kow within the QSAR domain as a lower estimate of the Koc of category members. The calculated log Koc is >6.2.