Lindane Diffusion in Soils: I. Theoretical Considerations and Mechanism of Movement

Equations are developed to describe the combined vapor and “nonvapor” phase diffusion of a volatile insecticide in soils and compared with the diffusion of lindane in a Gila silt loam in a transient state system. The quantity of diffused lindane appears to increase linearly with increased lindane concentration in the treated soil up to about 20 ppm but deviates from linearity at higher concentrations. The diffusion coefficient of lindane is independent of time until 22 ppm of the initial 80 ppm lindane concentration in the treated soil have diffused into the formerly untreated soil. The diffusion rate then decreases rapidly. The dependency of the diffusion coefficient on concentration and time may be explained by the fact that lindane will reach maximal vapor density in the range of 20 to 30 ppm. After these concentrations are built up in the initially untreated half‐cells by diffusion, vapor diffusion approaches zero and all the diffusion is in the “nonvapor” phase. At a 10% soil water content, 50% of the lindane diffuses in the vapor phase and 50% in the “nonvapor” phase. At near saturation, total diffusion is in the “nonvapor” phase. Lindane diffusion in soils can easily change from “nonvapor” to vapor phase and back to “nonvapor” phase.