ABSTRACT
The photodegradation of xenobiotics in the surface layers of natural waters can be the deciding mechanism to restrict their persistence in the aquatic environment. Under certain conditions photolysis is the main degradation pathway for these compounds, which are only slightly eliminated by biological or other chemical reactions. This appears to be the case for several synthetic chelating agents, eg ethylenediamine tetraacetic acid (EDTA), diethylenetriamine pentaacetic acid (DTPA), ethylenediaminetetra (methylenephosphonic acid) (EDTMP), 2-phosphono-butane-1, 2, 4-tricarbonic acid (PBTC) and 1hydroxyethane-1, 1-diphosphonic acid (HEDP). Due to their various applications as detergent builders, antiscaling agents, metal scavengers, corrosion inhibitors, antioxidants, cooling water conditioners etc.,1-3 considerable amounts are discharged with industrial or municipal sewage. Due to the small removal efficiency of conventional sewage treatment plants for bioresistant séquestrants, remarkable levels, especially of EDTA and DTPA are reaching surface waters. Considering the fact that chelating agents are assessed repeatedly to be the prevailing fraction of organic surface water pollutants, the investigation of their photoreactivities is of high environmental significance.4-7
Predominantly photodegradation experiments were conducted using technical light sources instead of natural sunlight. This offers the advantages of experimental conditions, which are independent from marginal factors such as geographic location, season, climatic (atmospheric) conditions, day time, etc. The irradiation can be regulated which facilitates time-lapse effects. Test reproducibility and comparability can be established. To date, with the focus on the choice of adequate light sources, the experimental conditions are still not standardized.
