The accumulation of herbicides in the environment as a consequence of their intensive usage associated to their high persistance is a matter of principal concern due to their harmful effects on the fauna and flora. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) is one of the worldwide mostly used herbicides, and is being detected in considerable amounts in aquatic and soil ecosystems. The goal of this study was to evaluate the sorptive behaviour of atrazine in a Humic Cambisol under its natural form and in the absence of organic matter. Sorption isotherms of commercial atrazine were determined in samples of an A horizon in its natural state and in an oxidized sample. The maximal quantity of sorbed herbicide ranged from 8 % (oxidized sample) to 49 % (natural sample) of the added amount. The Freundlich model in the linear form was applied to the experimental data and high correlation coefficients were obtained in both the natural sample (R = 0.960, P < 0.01) and the oxidized sample (R = 0.932, P < 0.01). The Freundlich coefficient (n f = 1.40) obtained in the natural samples indicates that the sorbate affinity for the sorbent increased with the adsorption increment, while in the oxidized sample the opposite behaviour was observed (n f = 0.78). The Freundlich coeficient Kf was 1.10 L kg-1 for the natural sample and 0.84 L kg-1 for the oxidized sample, and the distribution coefficient Kd ranged from 4.64 to 0.33 L kg-1, respectively. These results show that the organic matter was the most relevant atrazine sorbent in the Humic Cambisol. Furthermore, the K OC value of 103 L kg-1, classifies the commercial atrazine as of high mobility in the studied soil-atrazine system.
herbicide; Freundlich; organic matter; chemical affinity