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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
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Study type:
indirect photolysis
no guideline followed
Principles of method if other than guideline:
Hydrogen peroxide is cleaved by photolysis and the indirect photchemical degradation through OH radicals is measured using gas chromatography.
GLP compliance:
Analytical method:
gas chromatography
other: Photospectroscopy
Light source:
other: pressure mercury lamp
Light spectrum: wavelength in nm:
> 290
Details on light source:
Philips HPK 125 W high pressure mercury lamp
Type of sensitiser:
OH radical
237 d
Transformation products:
not specified

A relative rate method was used to determine the degradation of styrene by OH radicals in water, produced by the photolysis of H2O2.


Table: Relative OH- and RO2 -radical reaction rate constant and half-life:




τ (Tage)


3.37 x 109

~ 0.1



The relative rate constant was 3.37 x 10^9. Correcting this for an OH concentration of 10^-17 mol/L, this produces a half-life of 237 days for this degradation route (BUA, 1990).

Validity criteria fulfilled:
not applicable
Executive summary:

Styrene was tested for phototransformation in water. The Rate constant was determined to be 3.37 x 10^9 cm3 • molecule-1• s-1, the half live is 237 d.


Description of key information

A half-live of 237 d can be estimated in Mansour (1985).

Key value for chemical safety assessment

Half-life in water:
237 d

Additional information

Styrene does not adsorb solar radiation appreciably at wavelengths greater than 300 nm, therefore degradation of styrene by direct photolysis is unlikely. Mansour (1985) studied the indirect photolysis of styrene in water by reaction with hydroxyl radicals. Using the observed relative rate constant and assuming an OH-concentration of 10 E-17 mol/L a half-life of 237 days can be estimated. Indirect photolysis is therefore not a relevant degradation process in water in comparison to volatilisation and biotransformation.