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EC number: 240-521-2
CAS number: 16470-24-9
Minimum DT50: 302 min
Fluorescent Whitening Agents such as CAS
16470-24-9 have the ability to absorb part of the terrestrial
UV-sunlight (λ = 300 – 400 nm) and transform it into visible, blue
For that reason they are potentially
photodegradable substances. In an experiment on the elimination of CAS
16470-24-9 in an eutrophic lake water irradiated by sunlight, rapid
direct photolysis was reported (t1/2 < 6 hours). Several extensive
studies were performed.
The results indicate that photochemical
processes induced by sunlight are sufficient to degrade the test
substance. In natural waters these processes may be their main
degradation pathway since biodegradation is practically not existent.
The isomerization process appears to play
a major role in the photochemical behaviour. A constant isomer mixture
is maintained during photochemical degradation processes. Since the
photoisomerization process is temperature - as well as wavelength-
dependent, the isomer distribution changes in sunlit natural waters with
season (temperature) and depth (wavelength).
Fluorescence lifetimes decrease and
Z/E-isomer ratios increase with increasing temperature, which can be
interpreted in terms of an activated rate process in the first excited
singlet state of the E-isomer having activation energy of 20-26 kJ/mol.
The photodegradation rates of the
substance in natural sunlight are fast enough to be significant in the
photic zone of lakes and rivers. On clear summer days the half-lives
range from about to 4 to 5 hours for the test substance near the surface
of natural waters.
The importance of the photodegradation in
water does however strongly depend on the light screening of the water
constituents. The presence of suspended solids or sediments in natural
waters does not seem to have a major impact on the photoreactivity. The
extent of adsorption at environmental relevant pHs is rather small.
Thus, the small amounts of particles in the photic zone of natural
surface waters are not capable of adsorbing larger amounts of the
substance. The particles may however reduce the availability of light
since they adsorb light themselves.
In suspensions containing larger amounts
of particles the presence of particles may lead to a shift in the
photostationary state of the isomers.
Photoisomerization quantum yields and
isomer distributions at the photo stationary state affect the rates of
photodegradation of the Fluorescent Brighteners. With an equation
containing these values one can successfully calculate photodegradation
rate coefficients under natural sunlight conditions. The
photoisomerization is caused by an activated rate process in the first
exited singlet state. Additional radiationless deactivation channels
could be promoted by a limited torsion of the excited singlet E-isomer
about the C-C double bond, which would be allowed since the bulky
substituents at the double bond are highly flexible. The activation
energy for photoisomerization is low and somewhat influenced by the
viscous drag on the twisting group about the C-C double bond caused by
the bulky substituents. The bulkiness of the substituents is very
similar within the category. As a consequence of these mechanisms, all
substances of the category behave very similar with respect to
photoisomerisation and direct photolysis in sunlit aqueous solutions.
In conclusion, photodegradation is
expected to be an important elimination process for the substance under registration
in the upper layer of surface waters.
As a consequence, the photodegradation
process will lead to the formation of photodegradation products. Based
on the studies performed on CAS 16090-02-1 the chemical constitution of
the degradation products can be hypothesized (see attachment).
It is important to underline that most of
the aquatic toxicity tests are conducted under normal light conditions,
therefore water toxicity results will represent the realistic case in
which the parent and degradation products are present as would be the
case if the this substances were directly released into the environment.
Two fish acute toxicity tests are
available (Ciba-Geigy, 1994 and Novartis Services AG , 1998) on CAS
16090-02-1 pre-treated with light in order to obtain a high percentage
of photodegraded products and verify their impact on aquatic toxicity.
Both tests resulted in a LC50 > 100 mg/l, demonstrating that those
degradation products are no more dangerous for the environment than the
Information on Registered Substances comes from registration dossiers which have been assigned a registration number. The assignment of a registration number does however not guarantee that the information in the dossier is correct or that the dossier is compliant with Regulation (EC) No 1907/2006 (the REACH Regulation). This information has not been reviewed or verified by the Agency or any other authority. The content is subject to change without prior notice.Reproduction or further distribution of this information may be subject to copyright protection. Use of the information without obtaining the permission from the owner(s) of the respective information might violate the rights of the owner.
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