Mass balance for detergent-derived fluorescent whitening agents in surface waters of Switzerland

The two fluorescent whitening agents (FWAs) that are currently used in laundry detergents in Switzerland (DAS 1, a diaminostilbene, and DSBP, a distyrylbiphenyl) were studied in ten different Swiss rivers. Two-week-composite-samples were analyzed once a month for 1 year. In most of the investigated rivers, concentrations ranged from 6–120 ng l−1 for DAS 1 and from 10–70 ng l−1 for DSBP. Average per capita loads were 1.8 and 1.3 mg d−1 inhabitant−1 for DAS 1 and DSBP, respectively. Higher concentrations were found in rivers with densely populated catchment areas and below FWA manufacturing plants (DAS 1: 100–1000 ng l−1; DSBP: 50–1100 ng l−1). Only sampling locations situated below FWA manufacturing plants showed significantly increased per capita loads compared to the other stations investigated (8.0 mg DAS 1 d−1 inhabitant−1 at Weil (below Basel) on the river Rhine; 23.1 mg DSBP d−1 inhabitant−1 at Porte du Scex on the river Rhône). Thus, these FWAs can be applied as molecular markers for production wastewater. The measurements made in Swiss rivers allowed for the development of a mass balance for FWAs. This mass balance indicates that 13% of the FWAs being used are discharged to surface waters.