(488b) Cocrystal Engineering Strategy for Sustained Release and Leaching Reduction of Highly Water-Soluble Herbicide

As the most cost-effective tool for controlling insects, weeds, and microbes, chemical pesticides have been proven to be vital for public health and economic development. Each year, approximately 4 million tons of pesticides are used globally, with herbicides accounting for more than 2 million tons. Highly water-soluble herbicides, however, have brought some serious problems as a result of their great migratory capacity. To be specific, herbicides that leach into the water due to numerous factors, such as rainfall or irrigation, can dramatically impair the effectiveness, necessitating recurrent application. In addition, as the primary cause of groundwater pollution, herbicide-contaminated water resource poses a serious hazard to both environmental creatures and humans. Thus, maximizing pesticide efficacy while minimizing pollution has long been a priority in agricultural and environmental chemistry management of pesticide release and leaching behavior in soil. In this work, three cocrystals of herbicide metamitron were developed and further characterized by PXRD, SCXRD, Raman spectrum, TGA, and DSC. The herbicide cocrystals exhibited a considerable decrease in solubility and dissolution rate compared to pure MET. Molecular dynamics simulation calculations reveal that the enhancement of lattice energy plays a crucial role in reducing the solubility, which is also reflected in the reduced solvation sites from crystal structure analysis. Further, the soil column leaching experiments indicated that the cocrystals metamitron-naringenin and metamitron-baicalein greatly reduce the risk of leaching to groundwater. Greenhouse experiments demonstrated that the cocrystals of metamitron-naringenin and metamitron-baicalein could retain their herbicidal activity under two-weeks simulated rainfall conditions, whereas the pure MET was completely ineffective. This work demonstrates that cocrystal engineering can offer a promising strategy to achieve sustained-release efficacy and reduce environmental damage for highly water-soluble herbicides.