Sodium dodecylbenzenesulfonate

Phototransformation in water

Link to relevant study record(s)

Reference

Reference 1

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:

indirect photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

A study was conducted to determine the photodegradation of LAS in aqueous TiO2 dispersions. Experiments were carried out with 25 mL solutions containing LAS surfactant with TiO2. Some experiments used open vessels (37 mL Pyrex glass reaction vessels) under aerobic conditions. Others used vessels sealed with a rubber septum, the solution purged with argon and a fixed volume of oxygen injected. Spectrophotometric analysis was performed at regular intervals.

GLP compliance:

not specified

Radiolabelling:

not specified

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

> 330

Details on light source:

Xe lamp (450W)

Type of sensitiser:

other: aqueous solution with TiO2 particles

Concentration of sensitiser:

50 mg/L

Details on test conditions:

- Sensitizer : TiO2 suspension- Temperature : 25 deg C; during photolysis the solution temperature 35-40 deg C- Con. of subst : 50 ppm

Preliminary study:

Dodecylbenzene sulfonate is quickly decomposed when an aqueous solution of this compound is irradiated with light (λ> 330 nm) in the presence of TiO2 particles. The reaction proceeds in two steps: the decomposition of the aromatic ring occurs rapidly and is followed by oxidation of the alkyl chain. The adsorption of the surfactant on the surface of TiO2 makes the first step particularly effective even in the absence of catalysts such as noble metals. The application of this process in the detoxification of polluted waters is discussed

Details on results:

After 30 minutes the DBS have been decomposed and removal of the DBS absorption is complete after 2 hours of the light exposure.Rapid photodegradation (within 2 hours of light exposure) .Rapid (<1-2 hours) decomposition

Validity criteria fulfilled:

yes

Conclusions:

Rapid (<1-2 hours) decomposition. Dodecylbenzene sulfonate is rapidly photodegraded in aqueous aerated TiO2 suspensions. The reaction involves fast decomposition of the aromatic ring followed by slower oxidation of the aliphatic chain.

Executive summary:

Dodecylbenzene sulfonate is quickly decomposed when an aqueous solution of this compound is irradiated with light (λ> 330 nm) in the presence of TiO2 particles. The reaction proceeds in two steps: the decomposition of the aromatic ring occurs rapidly and is followed by oxidation of the alkyl chain. The adsorption of the surfactant on the surface of TiO2 makes the first step particularly effective even in the absence of catalysts such as noble metals. The application of this process in the detoxification of polluted waters is discussed

Reference 2

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:

indirect photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

A series of photodegradation studies were conducted. Aqueous solution of LAS (pH 6.75) were passed through an irradiated tubular flow reactor. Reaction rates were obtained for both non-sensitized conditions and when ferric perchlorate (0.04 to 3.15 x 10-4 g-mole/L) was used as a sensitizer. A Hanovia 1200-watt mercury-vapor lamp was the source of radiation. The LAS concentration was determined by the methylene blue method. Appropriate controls were used.

GLP compliance:

not specified

Radiolabelling:

not specified

Light source:

other: Mercury vapor lamp

Light spectrum: wavelength in nm:

>= 200 - <= 350

Details on light source:

Mercury vapor lamp : Hanovia 1200-WATT

Type of sensitiser:

other: Ferric perchlorate

Details on test conditions:

- Initial DBS concentration : 60~80 mg/L- Seneitizer : Ferric perchlorate- Temperature : 28 deg C- The ferric perchlorate solutions were made by FeOH and dissolving it in an aqueous solution of HClO4.- The DBS concentration was determined by the meyhlene blue method.

Preliminary study:

>95% photolytic degradation after 20 minutes

% Degr.:

> 95

Sampling time:

20 min

Details on results:

The sensitized rate of decomposition is two orders of magnitude than the nonsensitized rate.. All the DBS was converted to intermediate products at a residence time of 1 minute and 7 moles of CO2 were produced per mole of DBS in 20 minutes. Rapid photodegradation

Validity criteria fulfilled:

yes

Conclusions:

>95% photolytic degradation after 20 minutes.The sensitized rate of decomposition is two orders of magnitude than the nonsensitized rate..All the DBS was converted to intermediate products at a residence time of 1 minute and 7 moles of CO2 were produced per mole of DBS in 20 minutes. Rapid photodegradation

Executive summary:

Complete conversion of LAS to intermediates at an average residence time aslow as 1 minute. The maximum conversion to CO2 was obtained at aresidence time of 20 minutes and corresponded to 7 moles CO2 per mole ofLAS. Reaction rate increases by two orders of magnitude in presence offerric perchlorate. Half order kinetics with respect to light intensity and LASconcentration explained the data for nonsensitized conditions. Anappropriate rate equation could be derived by assuming a second-orderdeactivation of light-activated LAS molecules. The sensitized reaction wasbelieved to occur by abstraction of hydrogen atoms from LAS by hydroxylradicals. Hydroxyl radicals presumably are produced by an electron-transferreaction involving light-activated ferric ions. The mechanism is complex;over-all kinetics indicated a first-order effect of (Fe+3), 1.2 order in lightintensity, and maxima in the rate for intermediate LAS and O2concentrations.

Reference 3

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:

indirect photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

The effects of humics on the photolytic degradation of LAS was studied. Soil humic substances were extracted by a cationic exchange resin/water suspension from a humic podzol. Water-soluble synthetic humic substances were prepared by autoxidation of pyrogallol in alkaline solution. Aqueous solutions of 15 mg/L humic substance and 100 mg/L LAS were irradiated with a mercury lamp. Photometric measurements were performed with a spectrophotometer for recording the changes caused by photolysis at definite times at 223 nm for LAS.

GLP compliance:

not specified

Radiolabelling:

not specified

Light source:

other: Mercury lamp

Light spectrum: wavelength in nm:

> 400 - < 580

Details on light source:

Spectrum: 223 nm

Type of sensitiser:

other: Humic substances

Details on test conditions:

Temperature : 20 deg C

Preliminary study:

The presence of humic substances delayed the photodegradation.

Details on results:

LAS is a photolabile compound and that the rate of degradation is affected in the presence of humic substances. The effect is explained following ;1) Humic substances acted as efficient UV-absorbers.2)The reaction between humic substnaces and LAS is demonstrated by electostatic repulsion because of the negatively charged components at given pH.

Validity criteria fulfilled:

yes

Conclusions:

Photodegradation of LAS was reduced by humic substances by a factor of 2 or more. The aliphatic side chains are degraded first, followed by aromatic ring cleavages. Degradation follows first order kinetics both with and without the presence of humics.

Executive summary:

The presence of humic substances delays photodegradation of LAS, primarily because they act as UV-absorbers. The reaction between humicsand LAS is dominated by electrostatic repulsion because of the negatively charged components at the given pH. The hydrophobic interaction between humics and LAS is relatively weak compared to the electrostatic repulsion. Possibly the sulfonic groups from LAS may be bound by metal bridges to humic surfaces. The study used humic substance with a relatively high proportion of aromatic carbon; whereas a lower proportion is more typical in natural environments. Therefore, the difference in photolysis rate is likely to be less pronounced.

Description of key information

After 30 minutes the Sodium dodecylbenzenesulfonate (DBS) have been decomposed and removal of the DBS absorption is complete after 2 hours of the light exposure.Rapid photodegradation (within 2 hours of light exposure) .
Dodecylbenzene sulfonate is rapidly photodegraded in aqueous aerated TiO2 suspensions. The reaction involves fast decomposition of the aromatic ring followed by slower oxidation of the aliphatic chain. 

Key value for chemical safety assessment

Half-life in water:

2 h

Additional information

Data are available on the photodegradation of Na-C12 LAS in water.

The results are as follows:

Table   Photodegradations of Na-C12 LAS

Light source	Light spectrum	Test material	Result	References
Xe lamp	>330 nm	Sodium dodecylbenzenesulfonate	Rapid (<1-2 hours) decomposition	Hidakaet al., 1985
Mercury vapor lamp	200-350 nm	Sodium dodecylbenzenesulfonate	>95% photolytic degradation after 20 minutes	Matsuura and Smith, 1970
Mercury lamp	400-580 nm	Sodium dodecylbenzenesulfonate	The presence of humic substances delayed the photodegradation	Hermannet al., 1997