ARGENTINEAN SOILS AND /MONTMORILLONITE-CARBON SYSTEMS: ADSORPTION BEHAVIOUR AGAINSTS TWO DIFFERENT PESTICIDES.

MONTES, LUCIANA; FERNÁNDEZ, MARIELA; DIEZ TASCÓN, JUAN MANUEL; TORRES SÁNCHEZ, ROSA MARÍA; ZELAYA SOULÉ, MARÍA EMILIA; SUAREZ GARCIA, FABIAN

Congreso; XVI International Clay Conference; 2017

The addition of pesticides to the soil to maintain the yield in the agricultural production generates concern about the soils and waters contamination. Among the available remediation techniques, amendments with activated carbons have been used with success to restore contaminated soils [1]. The adsorption capacity of montmorillonite combined with that of carbon can be considered as an economic and alternative system to activated carbon for this purpose. Thiabendazole (TBZ) and Chlorpyrifos (CPF) are the main pesticides applied in Argentina, in fruit production, but their behaviour in cultivated soils as well as in montmorillonite-carbon systems (MCS) has not been yet evaluated. In this work we have studied Thiabendazole and Chlorpyrifos sorption on nine different surface soils and MCS. Characterization of the products obtained following interactions of both pesticides with MCS was conducted in order to understand the nature of sorption surface sites involved. The MCS synthesis was performed in similar procedure to that reported by Martin-Jimeno et al. [2]. An Argentinean montmorillonite from Rio Negro province was used, as carbon support. An aqueous suspension of 10 mg/ml of montmorillonite was prepared and then 5, 10 or 25 mg/ml of dextrose was added. The obtained suspension was sonicated by3 h and then maintained at 180oC during 16 h in a hydrothermal reactor. The resultant material (MCS-5, MCS-10 and MCS-25) was washed and dried at 60oC. MCS sorbents were characterized by nitrogen physical adsorption, XRD and SEM. Some soil characteristics, such as clay content, surface area and organic carbon (OC) were also determined by conventional methods. MCS with the adsorbed pesticides were characterized by FTIR measurements.Pesticide sorption studies were performed at room temperature in batch conditions, using 25 mg/ml of TBZ or CPF, ratio solid-solution=0.8 g/l, pH=6 and 24 h of contact time. The amounts of TBZ or CPF adsorbed were determined as the difference between the initial concentration and that at equilibrium determined by HPLC.The surface area measured for all MCS samples resulted of around 1m2/g. XRD showed that the montmorillonite structure of all MCS samples was not modified by the hydrothermal treatment, while SEM analysis showed laminar structures without presence of free dextrose. The studied soils exhibited clays content, surface area values and OC ranges between: 17-54 %, 12 and 39 m2/g and 1 and 5 %, respectively. TBZ sorption percentages on the different soils varied between 5 and 68% and the sorption capacity resulted positively correlated with clay content (Pearson correlation coefficient=0.88). Similar results were observed for CPF sorption, giving a Pearson correlation coefficient=0.73). Non correlation was observed between OC soil content and pesticides sorption on soils. Relatively high sorption percentages of TBZ on the MCS samples were obtained (around 95%). The FTIR spectra of the adsorbed pesticides showed peaks corresponding to TBZ and CPF in the MCS.These preliminary results indicated the capacity of MCS sorbents to retain the pesticides studied and their potential use as soil amendments.