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Environmental fate & pathways

Phototransformation in water

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Administrative data

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
disregarded due to major methodological deficiencies
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: Study seems to be well conducted, but not sufficiently detailed and results with atypical units.

Data source

Reference
Reference Type:
publication
Title:
UV photodegradation of phenolic aldehydes present in industrial wastewaters.
Author:
Benitez FJ; Beltran-Heredia J; Gonzalez T; Rea F
Year:
1997
Bibliographic source:
Journal of Environmental Science and Health, Part A: Environmental Science and Engineering & Toxic and Hazardous Substance Control, A32(9 & 10), 2599-2612

Materials and methods

Study type:
direct photolysis
Principles of method if other than guideline:
Substance irradiation in an annular photoreactor with polychromatic Hg lamp
GLP compliance:
not specified

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
Vanillin (4-hydroxy-3-methoxy benzaldehyde) was purchased at Sigma Chemical Co. (analytical grade)

Study design

Details on sampling:
no data
Buffers:
- pH: From pH 2 to 9 (Cf result table)
- final molarity of buffer: molarity = 10E-2 M
- Composition of buffer: pH was buffered by adding
Light source:
other: High pressure mercury lamp and artificial
Details on light source:
Remark:
Wavelenght in nm for high pressure Mercury lamp: ca. 239- ca. 385
Artificial light source:
- Emission wavelength spectrum: Hg polychromatic lamp; wavelength from  185 to far into visible light region.
- Light intensity at sample: 4.52x10E-5 Eins/s
Details on test conditions:
Test medium: No details
Replication: No details
Duration of test at given test conditionopen allclose all
Reference substance:
no
Dark controls:
no

Results and discussion

Spectrum of substance
Parameter:
max lambda
Value:
334 nm
% Degradationopen allclose all
% Degr.:
59.5
Sampling time:
40 min
Test condition:
Direct photolysis
Test condition:
Indirect photolysis
Transformation products:
not measured

Any other information on results incl. tables

The results refer to direct photolysis. The degradation products were not  looked up.
The result presented in the "direct photolysis" box is determined after  20 min of irradiation, at a temperature of 20 degC and a pH value of 7.
The main results are gathered in the table below:

TABLE 1: Conversions of vanillin obtained after 20 and 40 minutes:
Temperature    pH    conv at 20 min    conv at 40 min    Quantum yields
    (deg.C)                         (%)                      (%)                       L/Eins
      10                7             31.3                    49.8                      5.12
      20                7             34.6                    59.5                      6.41
      30                7             37.5                    62.1                      7.26
      40                7             44.4                    37.7                      8.48
      20                2             60.4                    79.7                      11.78
      20                5             28.7                    49.8                      5.49
      20                9             31.3                    53.6                      5.90

Vanillin photodegradation is not influenced by pH, when the values are  between 5 and 9. In more acidic conditions (pH=2) the photolysis increases 

drastically. After 40 min of irradiation, at pH equal to 5, 7  or 9, the photodegradation is around 30%, while at pH 2, the degradation is twice higher.
For pH above 5, the quantum yields can be correlated as a function of the  temperature in the form:
Quantum yield (L/Eins)=1081.4exp(-1518/T)          with T in deg C.

Final conversion values of vanillin, in a mixture with 3 other phenolic  aldehydes, after 70 minutes:
Temperature      pH      conversion value
      (deg. C)                           (%)
       10              7                39.9
       20              7                41.6
       30              7                45.0
       40              7                49.2
       20              2                67.8
       20              5                39.6
       20              9                36.4

The results for vanillin are from a study previously published (Benitezet  al., 1997). In the present work Vanillin is considered as model compound,  

basing the discussion of the results on the elements already presented in  the previous paper.
The conversion values are lower than those previously reported because in  this case, the medium is more complex due to the presence of the 

three  other phenolic compounds.

With H2O2 alone, no degradation of vanillin occurs. When H2O2 and UV  radiation were applied together, the kinetic constants values depend on  

the experimental conditions, as presented in the following table.

Temperature     H2O2 x 10E3     pH         k'                   kx10-4
    (degC)               (mol/L)            7      (1/Eins)             (L/mol.s)
       20                 2.97                  7          172                  172
       20                 4.28                  7          190                  190
       20                 5.60                   7         197                  197
       10                 4.23                   7         108                  108
       30                 4.26                   7          287                 287
       40                 4.19                   7          624                 624
       20                 4.23                   5            93                 358
       20                 4.31                   9            93                   71

After regression analysis (no statistical details were provided), an  Arrhenius expression, combining temperature and pH, was proposed:
K (L/(mlo/s))= 3.67x10E12exp(-5042/T)x[OH.]x10E-0.16


Applicant's summary and conclusion

Validity criteria fulfilled:
not specified
Conclusions:
The photolysis of vanillin by polychromatic UV radiation source permits  an important level of destruction in a moderately short time.