Disposition of Tetrachlorodibenzo-p-dioxin in Soil

The contamination of many sites in Missouri with 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) is without doubt the single most publicized and pressing environmental issue in Missouri. A recent model presented by R. A. Freeman and J. M. Schroy predicts that 90% of the TCDD at Times Beach has been lost through volatilization and subsequent photolysis during the ten years since initial contamination, furthermore, 57% of the loss was estimated to have occurred during the first summer. The loss of TCDD through volatilization has also been reported by R. G. Nash and M. L. Beall. It is apparent that the validity of the model can have a significant effect on the assessment of TCDD contamination in Missouri and similar contamination elsewhere. The two important parameters governing the loss from the soil bed are the initial depth profile, which is dependent on the carrier solvents (copollutants), and vapor phase diffusion within the bed. These two aspects were experimentally explored in the present study, with the objectives of monitoring the effects of carrier medium on depth of migration of TCDD in soil, and determining the extent of vapor phase diffusion in TCDD in soil. Study materials, methods and results are discussed.