Photoinduced decomposition of trichloroethylene on soil components

The photoinduced decomposition of trichloroethylene adsorbed on Ca-montmori llonite by long-wavelength UV irradiation has been studied in a quartz tube open to air or through which air or oxygen is passed. Solid-sample and liq uid-solution NMR techniques were used to identify apparent products or inte rmediates of the photodecomposition. Dichloroacetic acid was identified as a major organic product/intermediate; substantial amounts of pentachloroeth ane and trichloroacetic acid were also identified. The formation of CO2 was characterized quantitatively by wet chemical analysis. About 40% and 57%, respectively, of the total carbon of trichloroethylene was converted to car bon dioxide in air and O-2 environments over a period of 16 days; Phosgene and HCl were also defected. The photodecomposition of trichloroethylene ads orbed on whole soil, on Zn2+-exchanged and Cu2+-exchanged montmorillonites, on kaolinite, and on silica gel was also examined in less detail; qualitat ively, the conversion of trichloroethylene to dichloroacetic acid in a 48-h period occurred with the following order of decreasing efficiencies: Zn2+- montmorillonite > silica gel > kaolinite > Ca2+-montmorillonite > whole soi l > Cu2+-montmorillonite. These results show that the photoinducecl decompo sition of adsorbed trichloroethylene occurs on a variety of adsorbents, gen erating products and intermediates that are similar to what have been repor ted previously for TiO2-based photodecomposition but with much longer time scales. These conversions can, therefore, be expected to occur in sunlight at the air-soil interface.