Novel Formulations of Humic acid, Lignin, and Lignite Grafted Hydrogels for the Slow Release of Thiamethoxam

Abstract The objective of this study is to explore the novel use of natural polymers like Humic acid, Lignin, and Lignite based hydrogels for the formulation of pesticides and fertilizers that would reduce the residues in soil and run‐off water that pose a threat to human health and the environment. We synthesized hydrogels by grafting Humic acid, lignin, and lignite onto acrylic acid with N′N‐methylene bisacrylamide (MBA) for the ex‐situ encapsulation of thiamethoxam, a common pesticide. Various characterization techniques including Fourier‐transform infrared spectroscopy, Carbon‐13 Solid‐state Cross‐Polarization Magic Angle Spinning Nuclear Magnetic Resonance, X‐ray diffraction, Thermogravimetric Analysis, and Rheology were employed. The release kinetics of thiamethoxam in water from the developed formulations were analyzed using the Korsmeyer‐ Peppas model and the Weibull model. Humic acid and lignin‐based hydrogels exhibited a long‐sustained release for 49 hours, followed by lignite‐based hydrogels (38 hours). According to ANOVA results, the change of biopolymer proved to be an effective factor in reducing the water evaporation rate, which decreased from 99 % to 72.85 % in the soil amended with synthesized hydrogels. In conclusion, the novel formulations of humic acid, lignin, and lignite exhibit potential as slow‐release vehicles for pesticides and fertilizers. This study provides valuable insights for the research community, addressing the need to develop effective strategies for mitigating pesticide residues in soil and water bodies.