1-hydroxy-4-methyl-6-(2,4,4-trimethylpentyl)pyridin-2(1H)-one, compound with 2-aminoethanol (1:1)

Phototransformation in water

Description of key information

In this study Octopirox® was found to be highly photolytically unstable. The direct photolysis rate constant kd and half life t½ of the test item under laboratory conditions were determined to be 1.24 1/h (kd), 34 min (t½) for pH 9 and 3.09 (kd), 13 min (t½) for pH 4.

The correlation factor of the regression graphs of irradiated samples was ≥ 0.97, therefore pseudo first order kinetic model could be assumed.

The known transformation product NDO was formed under both test conditions. The estimated formation rate constants were significantly lower than the direct photolysis reaction rate constants of Octopirox® and therefore the formation of NDO could not be assumed as the solitary first step of the transformation pathway.

No unknown transformation products above 10 % of the initial active ingredient peak area were detected. At pH 4 no transformation products with UV detectable chromophores were observed after 125 h of irradiation. At pH 9 two groups of transformation products with differing UV absorption spectra were observed. The first group of transformation product with UV spectra comparable to the UV absorption spectrum of Octopirox® (maximum at approx. 303 nm) was vanished after 97 h of irradiation. The second group signals, with absorption maxima below 236 nm, showed increasing intensity up to 97 h of irradiation.

As a consequence of these observations it could be assumed that, resulting from the total termination of signals with an UV absorption maximum near 303 nm, the pyridinone ring system (chromophore) of the Octopirox® molecule was disintegrated by sunlight in up to 125 h of solar irradiation at 3060 µmol photons / s m2 (290-800 nm).

Key value for chemical safety assessment

Half-life in water:

34 min