The dynamic behavior of the two fluorescent whitening agents (FWAs) that are currently used in laundry detergents in Switzerland (DAS 1, a diaminostilbene, and DSBP, a distyrylbiphenyl) has been evaluated quantitatively during 1 year for Greifensee, a small lake in Switzerland, by using a one-box model and simulation software (MASAS) for modeling organic pollutants in lakes. Both the onebox model and the one-dimensional simulation were based on (i) independently evaluated processes affecting the fate of FWAs and (ii) measured FWA concentrations in the lake. 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 the elimination of DAS 1 and DSBP, respectively), sorption/ sedimentation (20% and 9%), and flushing (27% and 10%) were found to be relevant for FWAs in Greifensee. In particular, no evidence was found for other degradation processes such as biodegradation or hydrolysis. During 1 year, concentration depth profiles were measured above the deepest point of the lake in intervals of 4 weeks. The measured FWA 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 the first field validations for photochemical degradation rates measured in the laboratory. FIGURE 1. Structures of the FWAs included in this study. DAS 1, 4,4′-bis[(4-anilino-6-morpholino-1,3,5-triazin-2-yl)amino]stilbene-2,2′disulfonate; DSBP, 4,4′-bis(2-sulfostyryl)biphenyl.
Three different fluorescent whitening agents (FWAs) were examined in sediment cores of Greifensee, a small lake in Switzerland. Two of these FWAs (DAS 1 and DSBP) are currently used in domestic deter gents. The third one (BLS) was contained in detergents until some years ago. During sewage treatment, FWAs are only partly eliminated, and, hence, residual amounts reach the aquatic environment. They are partly associated with particles (K d = 30 -440 L/kg) and can, therefore, settle to the bottom of surface waters. This behavior and their persis tence to biodegradation allow the application of FWAs as molecular markers for domestic waste water. Total DAS 1 and DSBP inventories in the sediments of Greifensee were found to be 18 -270 mg/m 2 and 7 -80 mg/m 2 , respectively. Inventories of BLS ranged from 0.3-11 mg/m 2 . With increasing distance from the discharge points, FWA in ventories generally decreased. A sediment profile in Greifensee collec ted by means of a freeze core device shows the input history of FWAs from their first use in the mid 1960s. Because the equilibrium of FWAs in lake sediments between dissolved and particulate fraction lays strongly on the particulate side, remobilization in the sedimentary core is assumed to be negligible. Thus, concentrations in a particular sedi ment layer can be attributed to the inputs occurring at the time of depo sition.Detergents used for laundry washing and cleaning of surfaces are mixtures of different synthetic chemicals which are used in very large quantities. Worldwide con sumption of detergent products was estimated at 31 million tons per year in 1984 (7). The most important components, on a weight basis, are surfactants, builders, and bleaching agents. Other components are e.g. enzymes, foam regulators, dyes, and per fumes. To improve the whiteness of textiles, fluorescent whitening agents (FWAs, Figure 1) are added to laundry detergents in relatively small amounts of about 0.15% on a dry weight basis (2, 3). Exact quantities of FWA use are unknown, but estimates showed a world wide production of 14,0001 of DAS 1 and 3,0001 of others (predomi nantly DSBP) in 1989 (2). FWAs contained in detergents serve to replace textile FWAs which are photochemically degraded during wearing or are washed out during 1
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