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Environmental fate & pathways

Phototransformation in water

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Description of key information

In natural waters, the substance will be degradaded abiotically by phototransformation, followed by biological degradation of the resulting products. These transformation products are readily biodegradable.

Key value for chemical safety assessment

Additional information

In dilute solutions and in presence of sunlight, the substances undergos reversible isomerization of the stilbene moieties. In this process, two isomeric forms occur. The E,E- and E,Z-isomers are under environmental conditions in equilibrium within a few minutes. The concentration of a third isomer, (Z,Z), is negligible. The parent substance used as fluorescent whitening agent consists of the E,E-isomer. At solar latitude 60°, at 25°C, and on surface layer depths of 0 to 2m the remaining E,E-isomer fraction is 82% to 87% and 80% to 86%, respectively. The half-life for photo-oxidation in natural water (Lake Greifensee) was measured under the same light conditions on the surface layer: 87 ± 5 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. At a surface layer depth of 2 m the half lives range from 5 hours (Lake Lucern, summer) to 117 hours (Lake Greifensee, winter).

The photochemical degradation proceeds by oxidative degradation of the double bond yielding 2-sulfonic acid benzaldehyde and 4,4’-bisaldehyde biphenyl. Both photodegradation products are shown to be readily biodegradable in OECD test 301F.