Nanoformulation as a tool for improvement of thiamethoxam encapsulation and evaluation of ecotoxicological impacts

Huanglonbing, or citrus greening, is the most serious disease of citrus which cause large economic losses. One of the strategies to avoid the spread of the disease is the control of Diaphorina citri psyllid, its insect vector, by the application of insecticides. Development of nanoinsecticides, which are less harmful to the environment and more efficient (in terms of cost and performance) than the existing formulations, is a current challenge. In this work, nanocarriers composed of chitosan-tripolyphosphate (by ionic gelification approach) and poly-epsilon -caprolactone (PCL)-chitosan (by double-emulsion-solvent evaporation method) for thiametoxam insecticide were developed and characterized. Toxicological assessments using Raphidocelis subcapta, Artemia salina and Caernohabditis elegans were performed comparing PCL-chitosan nanoparticle and PCL-chitosan loaded thiamethoxam in comparison to commercial pesticide. The nanoparticles obtained from optimized conditions resulted in positive charged nanoparticles, with medium dispersity. The double-emulsion method resulted in smaller nanoparticles (313.5 +/- 7 nm) and increased encapsulation efficiency (36.6 +/- 0.2%) in comparison to chitosan-tripolyphosphate nanoparticles. The lower encapsulation efficiency was observed in chitosan-tripolyphosphate, impairing agricultural applications. The EC50 values (mg L-1) of Raphidocelis subcapitata and C. elegans obtained for poly-epsilon -caprolactone with thiamethoxam were 56.15 (18.91-131.21) and 66.07 (1.20-274.14), respectively, and poly-epsilon -caprolactone without thiamethoxam 94.26 (22.42-166.10) and 214.63 (139.08-494.3), respectively. No toxicity was found in Artemia salina. Our results indicate that nanoparticles (with and without thiamethoxam) were more toxic to soil organisms (C. elegan) than commercial formulations.