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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Ammonia is strongly adsorbed on soil, sediment particles and colloids in water.

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Additional information

Ammonia is strongly adsorbed on soil, sediment particles and colloids in water. This adsorption results in high concentrations of sorbed ammonia in oxidized sediments. Under anoxic conditions, the adsorptive capacity of sediments is less, resulting in the release of ammonia to either the water column or an oxidized sediment layer above. In clay, ammonium tends to be absorbed on the negative adsorption sites of clay colloids. Ammonia may substitute for potassium in the lattice structure of a clay mineral. Ammonia is bound in soil by the attraction of the positive charge on the ammonium ion to the negatively charged soil micelles. In soil, ammonium is adsorbed primarily by four mechanisms: chemical (exchangeable), fixation (non-exchangeable), reaction with organic matter and physical attractive forces.