Slow-release formulations of the herbicide picloram by using Fe–Al pillared montmorillonite

11 páginas.-- 8 figuras.-- 4 tablas.-- referencias.-- The online version of this article (doi: 10.1007/s11356-017-8699-9) contains supplementary material, which is available to authorized users.

Slow-release formulations of the herbicide picloram (PCM, 4-amino-3,5,6-trichloropyridine-2-carboxylic acid) were designed based on its adsorption on pillared clays (pillared clays (PILCs)) for reducing the water-polluting risk derived from its use in conventional formulations. Fe–Al PILCs were synthesized by the reaction of Na-montmorillonite (SWy-2) with base-hydrolyzed solutions of Fe and Al. The Fe/(Fe + Al) ratios used were 0.15 and 0.50. The PCM adsorption isotherms on Fe–Al PILCs were well fitted to Langmuir and Freundlich models. The PCM adsorption capacity depended on the Fe content in the PILCs. Slow-release formulations were prepared by enhanced adsorption of the herbicide from PCM-cyclodextrin (CD) complexes in solution. CDs were able to enhance up to 2.5-fold the solubility of PCM by the formation of inclusion complexes where the ring moiety of the herbicide was partially trapped within the CD cavity. Competitive adsorption of anions such as sulfate, phosphate, and chloride as well as the FTIR analysis of PCM-PILC complexes provided evidence of formation of inner sphere complexes of PCM-CD on Fe–Al PILCs. Release of the herbicide in a sandy soil was lower from Fe–Al PILC formulations relative to a PCM commercial formulation.

The authors acknowledge Universidad de Buenos Aires, Secretaria de Ciencia y Técnica Projects, Ministerio de Ciencia y Técnica, Agencia Nacional de Promoción Científica y Tecnológica, MINCyT-ANPCyT-FONCyT, and Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina (CONICET) for financial support. J.L.M-B acknowledges CONICET fellowship. This research was also supported by the MEC Project CTM2013-42306-R and the Junta de Andalucía Project P12-RNM1897. Both projects received funding by the European Social Fund. The authors also acknowledge the Analytical Services of Seville University (CITIUS) for SEM-EDS measurements.

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