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Environmental fate & pathways

Adsorption / desorption

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Description of key information

The test is not justified as bibliographic analysis supports the idea that perchlorate is more depositional than sorptive. Calculation of Koc made with KOCWIN v2.00 delivers a direct (MCI) Koc = 86.03 for ammonium perchlorate but warns that it is outside the validation domain.

Key value for chemical safety assessment

Koc at 20 °C:
86.03

Additional information

On the basis of physicochemical properties (high water solubility, negative log Kow), negligible adsorption coefficient is anticipated, so that testing is not required according to Annex VIII.

The bibliographic analysis which supports the idea that perchlorate is more depositional than sorptive is in published data by Urbansky, E.T. and Brown, S.K., in Perchlorate Retention and Mobility in Soils; J. Environ. Monit., 2003, 5, 455-462. Therefore the adsorption/desorption test for Perchlorate is not scientifically justified.

The sorption of ions on mineral surfaces depends on the degree of electronic charge of those surfaces. The presence of clay minerals or oxide surfaces, such as, iron oxide, enhances sorption. However, the perchlorate anion does not sorb readily onto clay minerals: although clays have appreciable cation exchange capacity, they typically have little anion exchange capacity. Thus based on its charge and the even charge distribution that results from the tetrahedral symmetry, perchlorate anion generally has a relatively low affinity for soils and mineral surfaces.