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Sorption and Desorption of Pesticides by Clay Minerals and Humic Acid-Clay Complexes

^a Department of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824
^b Department of Crop, Soil and Environmental Sciences, University of Arkansas, Fayetteville, AR 72701
^c Department of Agronomy, Purdue University, West Lafayette, IN 47907

View larger version (32K): [in a new window]   Fig. 1. Isotherms representing sorption of (A) 4,6-dinitro-o-cresol and (B) dichlobenil by Ca2+– and K+–saturated SWy-2 and SAz-1 smectite clays.

View larger version (32K): [in a new window]   Fig. 2. Isotherms representing pesticide sorption by reference smectite clays (SWy-2 and SAz-1) and the corresponding humic acid (HA)-clay complexes. Sorption of 4,6-dinitro-o-cresol by (A) K-HA-SWy-2/K-SWy-2, (B) K-HA-SAz-1/K-SAz-1, sorption of dichlobenil by (C) K-HA-SWy-2/K-SWy-2, and (D) K-HA-SAz-1/K-SAz-1. The lines represent the predicted curves obtained by summing up individual and independent contribution of humic acid and smectite clays to pesticide sorption.

View larger version (30K): [in a new window]   Fig. 3. Isotherms representing pesticide sorption by reference smectite clays (SWy-2 and SAz-1) and the corresponding humic acid (HA)-clay complexes. (A) Sorption of 4,6-dinitro-o-cresol by Ca-HA-SWy-2/Ca-SWy-2, (B) Ca-HA-SAz-1/Ca-SAz-1, (C) sorption of dichlobenil by Ca-HA-SWy-2/Ca-SWy-2, and (D) Ca-HA-SAz-1/Ca-SAz-1. The lines represent the predicted curves obtained by summing up individual and independent contribution of humic acid and smectite clays to pesticide sorption.

View larger version (36K): [in a new window]   Fig. 4. Sorption/desorption isotherms of pesticides in reference smectite clays (SWy-2, SAz-1) and the corresponding humic acid (HA)-clay complexes: 4,6-dinitro-o-cresol in (A) K-SWy-2, (B) K-HA-SWy-2a, (C) Ca-SWy-2, (D) Ca-HA-SWy-2b; and dichlobenil in (E) K-SWy-2, (F) K-HA-SWy-2a, (G) Ca-SAz-1, (H) Ca-HA-SAz-1.

View larger version (45K): [in a new window]   Fig. 5. X-Ray diffraction patterns of oriented films of (A) K-SWy-2, and the corresponding humic acid (HA)-clay complexes (B) K-HA-SWy-2a, and (C,D) the associated d-spacings as a function of 4,6-dinitro-o-cresol loadings.

View larger version (51K): [in a new window]   Fig. 6. The ratios of smectite to humic acid required to achieve 25, 50, and 75% of the total (A) 4,6-dinitro-o-cresol and (B) dichlobenil sorption by humic acid (HA) complexes of reference smectite clays (SWy-2, SAz-1).