Sorption of atrazine and simazine by model associations of soil colloids

The effect of association processes between single model soil components (i.e., Ca-saturated montmorillonite [CaSWy], ferrihydrite [Ferrih], and soil and commercial humic acid [HA]) upon their association in binary and ternary CaSWy-Ferrih-HA systems on physicochemical properties (specific surface area, pH, and basal spacing) and on triazine herbicide sorptive behavior was determined. Ferrihydrite coatings on CaSWy increased the specific surface area of the clay and slightly decreased pH, whereas HA coatings on CaSWy and Ferrih decreased both specific surface area and pH. Further association of HA with the CaSWy-Ferrih binary system decreased the specific surface area, but did not change the pH. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) sorption-desorption data showed that the sorptive behavior of the associations is not the simple sum of the sorption on single components. The HA association with CaSWy increased sorption of both herbicides by the clay, as suggested by an increase in sorption capacity (K∞) for the CaSWy-HA binary system. Although Ferrih did not sorb either triazine, Ferrih coatings on CaSWy increased sorption of both herbicides on the clay. The association of HA with Ferrih sorbed both triazines, but K(oc) decreased compared with HA alone. Further association of the CaSWy-Ferrih binary system with soil HA decreased the sorption, whereas association with commercial HA increased it. Desorption isotherms of atrazine and simazine showed that sorption by the model associations was reversible. | The effect of association processes between single model soil components (i.e., Ca-saturated montmorillonite [CaSWy], ferrihydrite [Ferrih], and soil and commercial humic acid [HA]) upon their association in binary and ternary CaSWy-Ferrih-HA systems on physico-chemical properties (specific surface area, pH, and basal spacing) and on triazine herbicide sorptive behavior was determined. Ferrihydrite coatings on CaSWy increased the specific surface area of the clay and slightly decreased pH, whereas HA coatings on CaSWy and Ferrih decreased both specific surface area and pH. Further association of HA with the CaSWy-Ferrih binary system decreased the specific surface area, but did not change the pH. Atrazine (2-chloro-4-ethyl-amino-6-isopropylamino-s-triazine) and simazine (2-chloro-4,6-bis(ethylamino)-s-triazine) sorption-desorption data showed that the sorptive behavior of the associations is not the simple sum of the sorption on single components. The HA association with CaSWy increased sorption of both herbicides by the clay, as suggested by an increase in sorption capacity (Koc) for the CaSWy-HA binary system. Although Ferrih did not sorb either triazine, Ferrih coatings on CaSWy increased sorption of both herbicides on the clay. The association of HA with Ferrih sorbed both triazines, but Koc decreased compared with HA alone. Further association of the CaSWy-Ferrih binary system with soil HA decreased the sorption, whereas association with commercial HA increased it. Desorption isotherms of atrazine and simazine showed that sorption by the model associations was reversible.Peer Reviewe