For a better handling of the herbicides during application, surfactants as wetting and dispersing agents are added to these substances. These surfactants change the hydrophobicity of the soil colloids and thus effect the herbicide sorption.

In this study sorption experiments were made with atrazine and simazine on the soil components Na⁺- kaolinite, Na⁺-illite, Na⁺-, Ca²⁺-, Ni²⁺-, Cu²⁺- and Fe³⁺-montmorillonite, respectively. To compare the results with real systems a subsoil sample, an orthic luvisol from Jülich-Merzenhausen, was also used. To study the effects of surfactants, the Ca²⁺-montmorillonite was treated with different surfactant classes.

The adsorption experiments showed that atrazine does not intercalate in Na+-montmorillonite, which is a swelling clay mineral, but is adsorbed on the external surface. The mechanism of adsorption on clay minerals is not a partitioning process, which is also confirmed by the desorption experiments. The found sorption hysteresis points to different binding mechanisms for different sorbents. Only partially reversible adsorption on Ca²⁺-montmorillonite and the soil sample occurs. That is more than one mechanism is responsible for adsorption. In contrast, the sorption on Fe³⁺-montmorillonite is totally irreversible.

If the clay surface is hydrophobized by surfactants (c < CMC), s-triazine adsorption is clearly increased. These processes can be adequately described by partition coefficients. A comparison of the influence of a cationic, an anionic and a nonionic surfactant on the atrazine sorption is given in consideration of the different adsorption behavior of the surfactants.