RADIOLYTIC DEGRADATION OF 2,3,7,8-TCDD IN ARTIFICIALLY CONTAMINATED SOILS

This paper reports results of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) destruction on artificially contaminated soil using cobalt-60 (Co-60) gamma radiation. Important parameters (soil moisture content, surfactant type/concentration, equilibration, and radiation dose) and their optimum ranges are identified. Scavenger (N2O, O2, 2-propanol) studies were conducted to explore the consequences of controlling oxidative and reductive conditions in the soil, and reaction byproducts have been analyzed under selected reaction conditions. A standard soil (EPA SSM-91) was artificially contaminated with 2,3,7,8-TCDD to 100 ppb, and in the presence of 25% water and 2% surfactant (RA-40) and at a high irradiation dose (800 kGy), greater than 92% TCDD destruction was achieved, resulting in a final TCDD concentration of less than 7 ppb. Results of scavenger and byproduct studies and theoretical target theory calculations indicate that TCDD destruction is caused primarily by direct radiation effects and proceeds through reductive dechlorination.