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Environmental fate & pathways

Phototransformation in water

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phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
according to GLP.
Study type:
direct photolysis
no guideline available
GLP compliance:
Analytical method:
high-performance liquid chromatography
Light source:
other: mercury immersion lamp
Light spectrum: wavelength in nm:
> 295 - < 490
Computational methods:
Using the Quantum yield, half-lives were calculated according to the GC-SOLAR and Frank and Klőpffer programs.
max lambda
243 nm
Quantum yield (for direct photolysis):
75.6 min
Predicted environmental photolytic half-life:
190 days
Transformation products:
not specified
Details on results:
Quantum yield (phi) = 0.006
Environmental direct photolysis half-life = 190 days

According to the GC-SOLAR program, the half lives are 3.0 day in summer and 52 d in winter (marginal conditions: pure water from close to the surface, 10th degree of longitude, 50th degree of latitude, clear sky, typical ozone concentrations in the atmosphere). According to the Frank and Klopffer program, the mean values of the half-lives range from 4.0 d in June to 190 d in December (marginal conditions: pure water from close to the surface, stagnant water, geographic and climatic conditions of 50th degree of latitude, no contribution of another mono- or bimolecular eliminiation process). The Frank and Klopffer model is probably closer to real environmental conditions, and corresponding values seem to be more valid. However, dullness and adsorption of surface waters are not considered. Because of these effects, the photolytical active zone is only close to the surface of real surface waters. Considering the total water body, the real environmental half-lives should be at least one order of range higher than the calculated value. Therefore a degradation rate constant of 3.6 . 10-4 d-1 (DT50 = 190 days) may be used in an exposure assessment.

Description of key information

4,4'-MDA exhibits an environmental direct photolysis half-life of 190 days when exposed to a wavelength between 295 and 490 nm in water.

Key value for chemical safety assessment

Half-life in water:
190 d

Additional information

A mean quantum yield of 0.006 was obtained from two photodegradation experiments. This value was used in two computer programs to provide so-called environmental half-lives for the direct photodegradation of 4,4'-MDA in water. The longest half-life of 190 days (December, 50th degree of latitude and no contribution from other mono- or bimolecular elimination processes) was obtained with the Frank and Klopffer program (Hellpointer & Dehner 1997).

Considering the total water body it is likely that the real environmental half-life is at least one order of magnitude higher than that calculated. Therefore a half-life of 1900 days may be considered to be more appropriate.

Experimental studies from Ekiçi et al., 2001 at different wavelength predicted environmental half-life times between 52.1 and 345 min, at the wavelength > 290 nm two transformation products were identified 4,4’ diaminobenzophenone and 4,4’ diaminobenzidine. These studies were rated not reliable due to major methodologic deficiencies. Nevertheless, these results can be taken into account as additional information.