Vapor Density of Soil‐Applied Dieldrin as Related to Soil‐Water Content, Temperature, and Dieldrin Concentration

Abstract Vapor densities of dieldrin (principal constituent HEOD‐hexachloro‐epoxyoctahydro‐endo, exo‐dimethanonaphthalene) in dieldrin‐soil mixtures increased with temperature and dieldrin concentration but were not affected by soil‐water content until the water content decreased below that equivalent of one molecular layer of water. Vapor densities dropped to very low values when the water content fell below this level, but increased again as water was added to the dry soil, indicating that the drying effect is reversible. When more than a monomolecular layer of water was present in the soil, vapor density increased with increasing soil dieldrin (HEOD) concentration until a saturation vapor density equal to that of HEOD without soil [54, 202, and 676 ng HEOD/liter at 20, 30, and 40C, respectively (9)] was reached at approximately 25 ppm HEOD. This implies that surface applications of dieldrin and probably other similar chlorinated hydrocarbon insecticides will volatilize as rapidly from mineral soils as from the pure materials until the concentration at the surface falls to relatively low levels. The data indicate that loss of water, per se, is not required for significant rates of volatilization to occur from soils or other surfaces on which water can successfully compete for adsorption sites.