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Phototransformation in water

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Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
direct photolysis
Principles of method if other than guideline:
Rates of reaction and product formation were measured in photodecomposition experiments of aqueous sodium chlorite at 253.7 nm in a reactor that was continuously sparged with nitrogen to remove chlorine dioxide.
GLP compliance:
not specified
Radiolabelling:
no
Analytical method:
other: a gas absorption system
Buffers:
The rate of photodecomposition of sodium chlorite was studied over a pH range of 4-10 and at unbuffered conditions.
Light source:
other: low-pressure mercury lamps
Light spectrum: wavelength in nm:
253.7
Details on test conditions:
The reactor was continuously sparged with nitrogen to remove chlorine dioxide.
Duration:
60 min
Temp.:
25 °C
Initial conc. measured:
0.1 mol/L
Reference substance:
not specified
Dark controls:
not specified
Transformation products:
yes
Details on results:
Rapidly removing chlorine dioxide greatly reduced the formation of chlorate.
The results of this work suggest that chlorate is not formed by direct decomposition of chlorite, but rather by decomposition of chlorine dioxide.
The results are consistent with the stoichiometry, 3 ClO2- + H20 (+hv) --> Cl- + 2 ClO2 + 2 OH- + 0.5 O2.Distribution of major products was not affected by pH; rates of reaction and chlorine dioxide formation were maximum at pH 6.For the former reaction, the values were 0.44 at 253.7 nm and 1.4 at 300 nm. For the latter reaction, the values at 253.7 nm ranged from 0.72 to 1.53, depending upon pH. Corresponding quantum yields for formation of chlorine dioxide ranged from 0.43 to 0.94, depending upon pH.

The rate of photodecomposition of sodium chlorite was studied over a pH range of 4-10 and at unbuffered conditions. Distribution of major products was not affected by pH; rates of reaction and chlorine dioxide formation were maximum at pH 6. Quantum yields were measured for both photodecomposition of chlorine dioxide and sodium chlorite. For the former reaction, the values were 0.44 at 253.7 nm and 1.4 at 300 nm. For the latter reaction, the values at 253.7 nm ranged from 0.72 to 1.53, depending upon pH. Corresponding quantum yields for formation of chlorine dioxide ranged from 0.43 to 0.94, depending upon pH.

Validity criteria fulfilled:
not applicable
Conclusions:
The rate of photodecomposition of sodium chlorite was studied over a pH range of 4-10 and at unbuffered conditions. Distribution of major products was not affected by pH; rates of reaction and chlorine dioxide formation were maximum at pH 6. Quantum yields were measured for both photodecomposition of chlorine dioxide and sodium chlorite. For the former reaction, the values were 0.44 at 253.7 nm and 1.4 at 300 nm. For the latter reaction, the values at 253.7 nm ranged from 0.72 to 1.53, depending upon pH. Corresponding quantum yields for formation of chlorine dioxide ranged from 0.43 to 0.94, depending upon pH.
Executive summary:

Rates of reaction and product formation were measured in photodecomposition experiments of aqueous sodium chlorite at 253.7 nm in a reactor that was continuously sparged with nitrogen to remove chlorine dioxide.

Rapidly removing chlorine dioxide greatly reduced the formation of chlorate. The results of this work suggest that chlorate is not formed by direct decomposition of chlorite, but rather by decomposition of chlorine dioxide. The results are consistent with the stoichiometry, 3 ClO2- + H2O (+hv) --> Cl- + 2 ClO2 + 2 OH- + 0.5 O2.

The rate of photodecomposition of sodium chlorite was studied over a pH range of 4-10 and at unbuffered conditions. Distribution of major products was not affected by pH; rates of reaction and chlorine dioxide formation were maximum at pH 6. Quantum yields were measured for both photodecomposition of chlorine dioxide and sodium chlorite. For the former reaction, the values were 0.44 at 253.7 nm and 1.4 at 300 nm. For the latter reaction, the values at 253.7 nm ranged from 0.72 to 1.53, depending upon pH. Corresponding quantum yields for formation of chlorine dioxide ranged from 0.43 to 0.94, depending upon pH.

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
direct photolysis
Principles of method if other than guideline:
The aim of this work was to study the photodecomposition of aqueous solutions of sodium chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of this substance. This report presents the data obtained for the identification of photoproducts.
GLP compliance:
not specified
Radiolabelling:
no
Analytical method:
high-performance liquid chromatography
other: colorimetric methods... (see attached file)
Light source:
other: mercury discharge lamp
Light spectrum: wavelength in nm:
253.7
Details on light source:
The two u.v. light sources mainly emit a monochromatic radiation at 253.7 nm (70% of the total photonic flux), and the radiations emitted at wavelengths higher than 253.7 nm are not negligible.
Details on test conditions:
Solutions of sodium chlorite were prepared in phosphate buffered ultra-pure water and irradiated at 20 ºC, in two cylindrical photochemical reactors equipped with a low pressure mercury vapour lamp.
Duration:
30 min
Temp.:
20 °C
Reference substance:
not specified
Dark controls:
not specified
Key result
DT50:
ca. 30 min
Test condition:
A steady increase in pH (pH 8 to 12.6)
Transformation products:
yes
Details on results:
Major products identified as hydroxide, chlorine dioxide and chloride with chlorate and hypochlorite as minor products and trace amounts of chlorine.

Irradiation of sodium chlorite solutions indicated a photodegradation half-life of about 30 minutes with a steady increase in pH (pH 8 to 12.6) and major products identified as hydroxide, chlorine dioxide and chloride with chlorate and hypochlorite as minor products and trace amounts of chlorine.

Validity criteria fulfilled:
not applicable
Conclusions:
Irradiation of sodium chlorite solutions indicated a photodegradation half-life of about 30 minutes with a steady increase in pH (pH 8 to 12.6) and major products identified as hydroxide, chlorine dioxide and chloride with chlorate and hypochlorite as minor products and trace amounts of chlorine.
Executive summary:

The aim of this work was to study the photodecomposition of aqueous solutions of sodium chlorite in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of this substance. This report presents the data obtained for the identification of photoproducts.

Solutions of sodium chlorite were prepared in phosphate buffered ultra-pure water and irradiated at 20 ºC, in two cylindrical photochemical reactors equipped with a low pressure mercury vapour lamp. The two u.v. light sources mainly emit a monochromatic radiation at 253.7 nm (70% of the total photonic flux), and the radiations emitted at wavelengths higher than 253.7 nm are not negligible. The concentrations of the initial compounds or of the photodecomposition by-products were determined by using colorimetric methods (chlorine dioxide, chlorine, dissolved ozone), high performance liquid chromatography (chlorite, chloride and chlorate ions), a polarographic cell (dissolved oxygen) or a total organic halogen analyser (total chlorine content; TOCl).

Irradiation of sodium chlorite solutions indicated a photodegradation half-life of about 30 minutes with a steady increase in pH (pH 8 to 12.6) and major products identified as hydroxide, chlorine dioxide and chloride with chlorate and hypochlorite as minor products and trace amounts of chlorine.

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
direct photolysis
Principles of method if other than guideline:
The decomposition of sodium chlorite by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis. The aim of this work was to study the kinetics of photodecomposition of sodium chlorite by u.v. irradiation.
GLP compliance:
not specified
Radiolabelling:
no
Analytical method:
high-performance liquid chromatography
other: colorimetric methods... (see attached file)
Light source:
other: mercury discharge lamp
Light spectrum: wavelength in nm:
253.7
Details on light source:
The two u.v. light sources mainly emit a monochromatic radiation at 253.7 nm (70% of the total photonic flux), and the radiations emitted at wavelengths higher than 253.7 nm are not negligible.
Details on test conditions:
Solutions of sodium chlorite were prepared in phosphate buffered ultra-pure water and irradiated at 20 ºC, in two cylindrical photochemical reactors equipped with a low pressure mercury vapour lamp.
Duration:
30 min
Temp.:
20 °C
Reference substance:
not specified
Dark controls:
not specified
Transformation products:
yes
Details on results:
The results obtained show that the pH and the initial concentration of sodium chlorite have no significant effect on the rate of photodecomposition of chlorite. These results also indicate that the radiation dose (9000 j/m2) needed to produce a 50% reduction in chlorite concentration suggests that the doses (200-250 j/m2) used for drinking water disinfection would not result in a significant reduction in chlorite concentrations.

The results obtained show that the pH and the initial concentration of sodium chlorite have no significant effect on the rate of photodecomposition of chlorite. These results also indicate that the radiation dose (9000 j/m2) needed to produce a 50% reduction in chlorite concentration suggests that the doses (200-250 j/m2) used for drinking water disinfection would not result in a significant reduction in chlorite concentrations.

Validity criteria fulfilled:
not applicable
Conclusions:
The results obtained show that the pH and the initial concentration of sodium chlorite have no significant effect on the rate of photodecomposition of chlorite. These results also indicate that the radiation dose (9000 j/m2) needed to produce a 50% reduction in chlorite concentration suggests that the doses (200-250 j/m2) used for drinking water disinfection would not result in a significant reduction in chlorite concentrations.
Executive summary:

The decomposition of sodium chlorite by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis. The aim of this work was to study the kinetics of photodecomposition of sodium chlorite by u.v. irradiation.

Solutions of sodium chlorite were prepared in phosphate buffered ultra-pure water and irradiated at 20 ºC, in two cylindrical photochemical reactors equipped with a low pressure mercury vapour lamp. The two u.v. light sources mainly emit a monochromatic radiation at 253.7 nm (70% of the total photonic flux), and the radiations emitted at wavelengths higher than 253.7 nm are not negligible. The concentrations of the initial compounds or of the photodecomposition by-products were determined by using colorimetric methods (chlorine dioxide, chlorine, dissolved ozone), high performance liquid chromatography (chlorite, chloride and chlorate ions), a polarographic cell (dissolved oxygen) or a total organic halogen analyser (total chlorine content; TOCl).

The results obtained show that the pH and the initial concentration of sodium chlorite have no significant effect on the rate of photodecomposition of chlorite. These results also indicate that the radiation dose (9000 j/m2) needed to produce a 50% reduction in chlorite concentration suggests that the doses (200-250 j/m2) used for drinking water disinfection would not result in a significant reduction in chlorite concentrations.

Description of key information

Weight of evidence

Published data:

The decomposition of sodium chlorite by u.v. radiation leads to the production of chlorate, chloride and oxygen as end-products via complex reactions which are initiated by the products generated by the primary reactions of photolysis. Irradiation of sodium chlorite solutions indicated a photodegradation half-life of about 30 minutes with a steady increase in pH (pH 8 to 12.6) and major products identified as hydroxide, chlorine dioxide and chloride with chlorate and hypochlorite as minor products and trace amounts of chlorine.

The photodecomposition of aqueous solutions of sodium chlorite was studied in u.v. reactors equipped with low pressure mercury vapour lamps in order to show the effects of pH and of the initial concentrations on the nature of photoproducts and on the rate of photodecomposition of this substance. The results obtained show that the pH and the initial concentration of sodium chlorite have no significant effect on the rate of photodecomposition of chlorite. These results also indicate that the radiation dose (9000 j/m2) needed to produce a 50% reduction in chlorite concentration suggests that the doses (200-250 j/m2) used for drinking water disinfection would not result in a significant reduction in chlorite concentrations.

Rates of reaction and product formation were measured in photodecomposition experiments of aqueous sodium chlorite at 253.7 nm in a reactor that was continuously sparged with nitrogen to remove chlorine dioxide. The rate of photodecomposition of sodium chlorite was studied over a pH range of 4-10 and at unbuffered conditions. Distribution of major products was not affected by pH; rates of reaction and chlorine dioxide formation were maximum at pH 6. Quantum yields were measured for both photodecomposition of chlorine dioxide and sodium chlorite. For the former reaction, the values were 0.44 at 253.7 nm and 1.4 at 300 nm. For the latter reaction, the values at 253.7 nm ranged from 0.72 to 1.53, depending upon pH. Corresponding quantum yields for formation of chlorine dioxide ranged from 0.43 to 0.94, depending upon pH.

Key value for chemical safety assessment

Half-life in water:
30 min

Additional information