DYNAMIC BEHAVIOR OF FLUORESCENT WHITENING AGENTS IN GREIFENSEE - FIELD-MEASUREMENTS COMBINED WITH MATHEMATICAL-MODELING OF SEDIMENTATION AND PHOTOLYSIS

The dynamic behavior of the two fluorescent whitening agents (FWAs) th at are currently used in laundry detergents in Switzerland (DAS 1, a d iaminostilbene, and DSBP, a distyrylbiphenyl) has been evaluated quant itatively during 1 year for Greifensee, a small lake in Switzerland, b y using a one-box model and simulation software (MASAS) for modeling o rganic pollutants in lakes. Both the one-box model and the one-dimensi onal simulation were based on (i) independently evaluated processes af fecting the fate of FWAs and (ii) measured FWA concentrations in the l ake. The relevant processes were derived from literature data and from measurements in the lake and in its tributaries. Besides loading from tributaries, only photodegradation (responsible for 53% and 81% of th e elimination of DAS 1 and DSBP, respectively), sorption/sedimentation (20% and 9%), and flushing (27% and 10%) were found to be relevant fo r FWAs in Greifensee. In particular, no evidence was found for other d egradation processes such as biodegradation or hydrolysis. During 1 ye ar, concentration depth profiles were measured above the deepest point of the lake in intervals of 4 weeks. The measured RNA concentrations were between 50 and 120 ng L-1 (DAS 1) and between 10 and 110 ng L-1 ( DSBP), with maximum Values in the thermocline during summer. Evidence was found that these maximum Values originated from subsurface loading occurring in summer at levels of 4-8 m depth. This study is one of th e first field validations for photochemical degradation rates measured in the laboratory.