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Environmental fate & pathways

Adsorption / desorption

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Description of key information

An estimation of an adsorption coefficient (Koc) on soil and on sewage sludge using HPLC is not possible to carry out because of a character of the test substance (inorganic mixtures (UVCB)). 

Key value for chemical safety assessment

Additional information

In accordance with section 2 of REACH Annex XI, Regulation (EC) No. 1907/2006,the study does not need to be conducted as estimation of the adsorption coefficient (Koc) on soil and sewage sludge using HPLC is not possible to carry out because of a character of cenospheres (inorganic UVCB substance with a multitude of variable constituents). Additionally the principle of the method used to test ist not suitable; HPLC on a reverse phase, which is not applicable for compounds of this character. A representable Kd calculation is therefore also not possible due to the multitude of unknown consitituents that define it’s UVCB character of the test substance, only a limited number of ranges for the main components and trace elements can be calculated. Log Kd values of 0.44 - 3.18 are calculated for the main components of fly ash oxides and Log Kd values of 4.2 - 4.88 are available for trace elements.

Adsorption potential to soil and sediment is therefore possible. The cenospheres under consideration consists mostly of oxides: SiO2, Al2O3,3and other compounds in amount less than 1%. In general soils contain up to 95% SiO2and other fly ash components such as Al2O3and Fe2O3are also present most common in soils. Since SiO2is a main element of fly ash, there is a natural relationship between it and soils where it may even build up own its own soil horizons and can be used as a fertilizer. Additionally, the cenospheres are hollow balls and the gas bubbles cause the cenospheres to be so lightweight that they float on water. They are typically collected by skimming the surface of an ash pond and an exposure to sediment can be excluded and an exposure to soil is also very unlikely.