Atrazine Adsorption by Some Soil Samples in Relation to Their Constituents

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Abstract
Atrazine adsorption from 0.01 M CaCI2 solutions was investigated using eleven soil samples from Denmark and Tanzania, and four “pure” soil constituents, i.e. EDTA-extracted humic acid, montmorillonite, so-called amorphous iron oxides, and goethite. Considerable amounts of atrazine were adsorbed by the humic acid, whereas only negligible amounts were adsorbed by the smectite and the iron oxides. Atrazine adsorption by the humic acid, in the pH range 4–8, was closely related to undissociated carboxyl and phenol groups, suggesting a rather specific adsorption mechanism, such as hydrogen bonding. For the soil samples, atrazine adsorption was only significantly (p<0.001) correlated with the organic matter (O.M.) content, but much more atrazine was adsorbed by soil O.M. than by the humic acid. Therefore, O.M. seems to be the only atrazine-adsorbing constituent in the soil samples investigated and possibly also in many natural soils.