Tricyclazole-Clay Complexes As Potential Smart Delivery Systems: Release in Water and Environmental Fate in Alluvial and Sandy Soils.

Tricyclazole (5-methyl-1,2,4-triazolo[3,4-b]benzothiazole) is a systemic fungicide used for the control of the rice blast disease caused by Pyricularia oryzae. This fungicide is applied by aerial fumigation on paddy fields and later is detected in surrounding waters.

Natural mineral clays (SWy-2, CTI and SH) were modified with natural inorganic cation (Fe³⁺) and the biopolymer (chitosan (ch)) to increase the adsorption capacity for tricyclazole. Three ways to prepare tricyclazole-clay complexes (ground mixing, GM, weak complex, WC and strong complex, SC) were assayed with the aim to develop possible components for controlled release formulations (CRFs) of this fungicide. The greatest adsorption (> 93%) was measured in the natural clays modified with Fe³⁺. The release of tricyclazole in water was higher for GMs of SWch6 (77%), SWch4 (84%) and CTIFe (85%). No significant differences were observed in the dissipation in soil of tricyclazole applied as commercial product or as formulation. However, the leaching of the fungicide depended on the type of soil: tricyclazole was not detected in any leachate from the soil with higher clay content (alluvial) whereas the SWch6 weak complex (WC) reduced the leaching of tricyclazole (65%) as compared to the commercial formulation (75%) in a sandy soil after 60 days. This last tricyclazol-clay complex could be considered as appropriate component for CRF, to be used in sandy soils. The other modified clays assayed, showing very high, strong and irreversible adsorption could find application as filters to eliminate tricyclazole from contaminated waters. Clay-fungicide interaction mechanisms are discussed and related to their soil and water behavior.

Acknowledgments: CSIC (JAE-Doc program), MINECO (AGL2011-23779 project) and Junta de Andalucía (P11-AGR-7400), co-funded by EU FEDER-FSE (OP 2009-2013) funding.