Adsorption of Atrazine on Smectites

Abstract

Smectites may strongly influence the fate of pesticides in soils due to their large surface area and abundance in agricultural soils. This research was undertaken to determine the effects of smectite properties on the affinity of smectitic clays for atrazine (2‐chloro‐4‐ethylamino‐6‐isopropylamino‐1, 3, 5 triazine). Samples of the <2‐µm fraction were separated by sedimentation from 13 reference smectites and treated with H2O2 for removal of organic matter. A soil smectite sample was separated (<0.02‐µm fraction) from a H2O2 and dithionite‐citrate‐bicarbonate‐treated Webster (fine‐loamy, mixed, mesic Typic Haplaquoll) soil by a dispersion‐centrifugation‐decantation technique. All 14 samples were Ca saturated, dialyzed free of excess electrolyte, and freeze dried. The mineralogy of each sample was evaluated by a combination of x‐ray diffraction and chemical analysis. Values for cation‐exchange capacity (CEC), surface charge density (SCD), surface area (SA), and percent tetrahedral charge (TC) were based on structural interpretations of the chemical analyses. Freundlich adsorption isotherms for atrazine adsorption on each sample were determined using the batch‐equilibration method. Smectite was the dominant mineral in 13 of the clay samples; the 14th sample was a mixture of interstratified smectite‐illite, quartz, and kaolinite. For the smectitic clays, atrazine adsorption ranged from 0 to 100%, and the logarithm of the Freundlich adsorption constant [log(Kf)] decreased linearly with the CEC (r2 = 0.82) of the clays. Stepwise multiple‐regression analysis indicated that log (Kf) values were correlated with SCD and SA values (r2 = 0.83). Inclusion of TC and suspension pH as independent variables in the regression analysis did not significantly improve the correlations. The results indicate that the affinity of smectites for atrazine decreases with increasing SCD, which suggests that atrazine is primarily adsorbed by smectites as a neutral species.

Lumbricid macrofauna alter atrazine mineralization and sorption in a silt loam soil

“…Methodological differences between flask-based and soil column-based microcosms as well as factors such as earthworm biomass to soil ratio, earthworm species, and physicochemical properties of the test soil may have also contributed to the differences among studies. In fact, since atrazine is cationic, its sorption to humic matter and clay is pH dependent (Khan, 1978;Laird et al, 1992). Nevertheless, there were no apparent systematic differences in the soils used by Meharg (1996); Gevao et al (2001) and the soils used by Farenhorst et al (2000b) and in our study that would suggest differences in atrazine mineralization.…”

Prediction of CEC Using Fractal Parameters by Artificial Neural Networks

“…The PTFs developed in this study are also related to smectitic soils that have quite different behaviours compared to soils with other dominant clay minerals, due to large surface area, high cation exchange capacities, chemically active surfaces, reversible interlayer expansibility (Laird et al, 1992), high potential of swelling and shrinkage with minimal horizon differentiation due to pedoturbation (Ahmad, 1983), wide and deep cracks as deep as 50 cm and at least 1 cm wide (Staff, 1975). In spite of numerous PTFs having been offered to predict CEC in different soils, fewer PTFs have been introduced to predict CEC in smectitic soils.…”

Sorção de atrazina em cambissolo húmico do Rio Grande do Sul sob vegetação nativa

“…O espectro da solução de atrazina (8 mg L -1 ) na região do UV/Vis apresentou um máximo de absorção em 222 nm, que é o comprimento de onda usualmente utilizado para a quantificação da atrazina quando se usa detector de UV (Barriuso et al, 1992;Martin-Neto et al, 1994). A ausência de um pico em 240 nm comprovou que as soluções empregadas nos testes de sorção não continham hidróxi-atrazina.…”

“…A sorção de atrazina na superfície de esmectitas e caulinitas ocorre principalmente por pontes de hidrogênio e por interações hidrofóbicas em superfícies de baixa densidade de carga (Laird et al, 1992;Sawhney & Singh, 1997;Herwig et al, 2001). Martin-Neto et al (1994), por meio de técnicas espectroscópicas, mostraram que as interações entre ácidos húmicos extraídos de um Oxissolo brasileiro e a atrazina ocorrem por pontes de hidrogênio e por ligações hidrofóbicas.…”