Verlag des Forschungszentrums Jülich
JUEL-3530 The s-triazines are worldwide used herbicides in weed control and can be found in
surface waters and also in different soil compartiments. In countries where the
application of atrazine is forbidden like in Germany since 5 years, these substances occur
even in groundwater samples. For a better understanding of the transport of these
pesticides in soil sorption investigations with native soil components are necessary. 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.
Herwig, Ulrich
Physikochemische Wechselwirkungen von s-Triazinen mit Bodenbestandteilen
106 S., 1998
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