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EC number: 224-548-7 | CAS number: 4404-43-7
Phototransformation in water
Administrative data
Link to relevant study record(s)
Description of key information
In surface waters, the substances in the stilbene fluorescent whitening agent category will be effectively degraded by photochemical processes.
Key value for chemical safety assessment
Additional information
In dilute solutions and in presence of sunlight,the substances in the stilbene fluorescent whitening agent categoryundergo 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 (for CAS 16090-02-1 and CAS 16470-24-9) 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 (CAS 16090-02-1) and 313 min (CAS 16470-24-9). 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.
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