Transformation efficiency and formation of transformation products during photochemical degradation of TCE and PCE at micromolar concentrations

Background: trichloroethene and tetrachloroethene are the most common pollutants in groundwater and two ofthe priority pollutants listed by the u.s. environmental protection agency. in previous studies on tce and pcephotolysis and photochemical degradation, concentration ranges exceeding environmental levels by far withmillimolar concentrations of tce and pce have been used, and it is not clear if the obtained results can be used toexplain the degradation of these contaminants at more realistic environmental concentration levels.methods: experiments with micromolar concentrations of tce and pce in aqueous solution using direct photolysisand uv/h2o2 have been conducted and product formation as well as transformation efficiency have beeninvestigated. spme/gc/ms, hplc/uv and ion chromatography with conductivity detection have been used todetermine intermediates of degradation.results: the results showed that chloride was a major end product in both tce and pce photodegradation. severalintermediates such as formic acid, dichloroacetic acid, dichloroacetaldehyede, chloroform, formaldehyde andglyoxylic acid were formed during both, uv and uv/h2o2 treatment of tce. however chloroacetaldehyde andchloroacetic acid were only detected during direct uv photolysis of tce and oxalic acid was only formed duringthe uv/h2o2 process. for pce photodegradation, formic acid, di- and trichloroacetic acids were detected in bothuv and uv/h2o2 systems, but formaldehyde and glyoxylic acid were only detected during direct uv photolysis.conclusions: for water treatment uv/h2o2 seems to be favorable over direct uv photolysis because of its higherdegradation efficiency and lower risk for the formation of harmful intermediates.