"This study on the aqueous chemistry, sorption, and mobility of hexachlorocyclopentadiene (C-56) in soil materials was initiated to provide information on its behavior in the environment, particularly on its movement through soil at land disposal facilities for hazardous wastes. Studies showed that the solubility of C-56 in water, soil extracts, and sanitary landfill leachates ranged from 1.03 to 1.25 ppm. Sodium hydroxide (caustic soda) and sodium chloride decreased the solubility of C-56 in water as the salt concentration increased; sodium hypochlorite slightly increased the solubility of C-56; and sodium perchlorate had no significant effects due to increasing salt concentration on the solubility of C-56. A caustic brine composed of a mixture of the salts was intermediate in decreasing solubility. The half-life of C-56 in water was about three months at both 22ÀC and 35ÀC, indicating little temperature dependence. C-56 is very photosensitive, and its half-life was less than four minutes in aqueous solution and less than 1.6 minutes in hexane or methanol solution. Studies also indicated that pH did not significantly affect the C-56 hydrolysis rate in aqueous solution; however, iron caused an increase in the hydrolysis rate. At least 12 products of photolysis and hydrolysis were identified. Pentachlorocyclopentenone, hexachlorocyclopentenone, pentachloropentadienoic acid, cis- and transpentachlorobutadiene, and tetrachlorobutenyne were the major products identified. The presence of salts in solution dramatically affected the sorption of C-56; brine, NaCI, and NaOH caused an increase in sorption while NaOCI caused a decrease in sorption. There was also a high direct correlation between the total organic carbon (TOO content of soils and the amount sorbed. C-56 remained immobile in the soils when leached with water, landfill leachate, or caustic brine but was highly mobile when leached with organic solvents. In a soil column leaching study, some hydrolysis products of C-56 were much more mobile than C-56, indicating they might migrate and generate environmental problems."