Slow diuron release formulations based on clay–phosphatidylcholine complexes

Abstract

Slow release formulations of the herbicide diuron were designed to reduce the risk of water pollution resulting from conventional formulations. The new formulations were based on herbicide incorporation in phosphatidylcholine (PC) vesicles that were sorbed on the clay mineral montmorillonite. The active ingredient contents of the formulations reached up to 28% w:w. Thermal analysis revealed that the closely packed arrangement of PC on the clay enhanced diuron sorption by disrupting the interactions among PC molecules. Adsorption experiments using diuron were performed in soils with different physico-chemical properties to evaluate the relationship between the sorption and the mobility of the herbicide. In soil column experiments with sandy soil, the herbicide in PC–clay-based formulations mainly accumulated in the top soil, and there was a one-third reduction in leaching compared to the commercial formulation. The differences in leaching (compared to the commercial formulation) were lower when using loam soil due to its higher sorption of the herbicide and hysteresis effects. In the sandy soil, bioassay experiments showed a higher herbicidal activity in the top-soil layer for the PC–clay formulations than for the commercial formulation. Therefore, PC–clay formulations of this herbicide can be used at lower doses than recommended, thereby reducing the environmental risks associated with the application of diuron formulations.