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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Kd (t=48h), Eurosoil 1: 50 mL/g
Kd (t=48h), Eurosoil 2: 15 mL/g
Kd (t=48h), Eurosoil 3: 14 mL/g
Kd (t=30h), Eurosoil 4: 19 mL/g
Kd (t=48h), Eurosoil 5: 3 mL/g

Key value for chemical safety assessment

Koc at 20 °C:

Additional information

All the studies were performed on the similar substance Reaction mass of dipotassium phosphonate and Phosphonic acid, potassium salt (1:1). Rationale for Read Across is attached at point 13.

A study on the Potassium Phosphonate KH2PO3/K2HPO3 was performed, with the aim of the determination of the adsorption behaviour on soils. Adsorption kinetics and equilibrium adsorption coefficients Kd with a single concentration on five soils were determined as a function of soil characteristics (organic carbon content, clay content, soil texture and pH value). These soils cover as widely as possible the interaction with natural soils. Furthermore the reversibility of adsorption (desorption behaviour) was investigate.

No organic carbon normalised distribution coefficients (Koc) were calculated since potassium phosphonate is an inorganic substance.


The highest degree of adsorption forPotassium Phosphonate KH2PO3/K2HPO3 was obtained in the soil with the highest amount of clay. In fact the results demonstrate under consideration of the soil parameters that there is a positive correlation between the degree of adsorption at equilibrium and the proportion of the clay fraction in the soils.

The organic carbon content does not influence the adsorption behaviour of the test item as expected for an inorganic compound.

The sand fraction is of low importance for the adsorption behaviour of the test item. In addition, as expected for an inorganic compound, the amount of organic carbon in the soil does not influence the adsorption behaviour of the test item. Therefore, no organic carbon normalised distribution coefficients Koc were calculated. Nevertheless, the results indicate that adsorption of the test item is significant on all soils.


The adsorbed mass on soil increased with a higher loading level of the test item in the aqueous phase. Only the results for the corresponding experiments in eurosoil 4 do not follow this behaviour.


Adsorption is at least partially reversible in all eurosoils. The most significant desorption behaviour was observed in eurosoil 4 and 5.

Due to the variability of the Kd values (different Eurosoils), a most conservative value of Koc at 20°C 771 (log Koc 2.89) was used for the CSA calculation in the CRS.

[LogKoc: 2.89]