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No significant hydrolysis was detected at pH values of 4, 7 ,and 9 at 50 °C after 5 days. The half life at ambient temperature was estimated to be greater than 1 year.

Phototransformation in water

In dilute solutions and in presence of sunlight,stilbene fluorescent whitening agentsundergo reversible isomerization of the stilbene moiety. In this process, two isomeric forms occur. The E- and Z-isomers are under environmental conditions in equilibrium within a few minutes. The parent substances used as fluorescent whitening agent consist of the E-isomer, while isomerization to the Z-form leads to complete loss of fluorescence. Two studies demonstrate that at solar latitude 60°, at 25°C, and on surface layer depths of 0 to 5m the remaining E-isomer fraction is 13.9 to 9.5 and 17.8 to 13.3, respectively. The preceding isomer equilibrium influences the photo-degradation rate. The half-life for photo-oxidation in natural water (Lake Greifensee) was measured for the same substances and under the same light conditions on the surface layer: 278 min and 313 min. The experimental kinetic data are used to calculate photochemical half-lives as a function of surface layer depth, optical density of the water, and time of the year.

Based on measured kinetic parameters and the quatum yield, photochemical half-lives in three Swiss lakes are calculated according to GCSOLAR as a function of surface layer depth and time of the year (Kramer, 1996). Both substances degrade with nearly identical half-lives. Therefore, it is assumed that all substances of the category follow the same photolytical processes and areeffectively degraded in surface waters.

A RIVM report (Plassche et al., 1999) shows that stilbene fluorescent whitening agents will be effectively degraded by photochemical processes. It is shown that first photoisomerization occurs, followed by photodegradation. Rates are rapid: half-lives are in order of 1 hour or even less. The US EPA property estimation program AOPWIN v 1.92 calculates a Half-Life of 6 hours (Hydroxyl Radicals reaction) and 2 hours (Ozone reaction) for a stilbene principle structure.

UV-VIS spectrum of the test item showed an absorption band with a maximum located at 350 nm. Therefore direct photo degradation is very likely.