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

Endpoint summary

Description of key information

AIR COMPARTMENT

DIRECT PHOTOLYSIS

Octopirox does absorb light >290 nm (ozone band) and therefore a direct photolysis in air may occur. Measurements on Direct Photolysis are not available but in water (see IUCLID Section 5.1.3). It can be expected that the Direct Photolysis in air is even faster than in water.

INDIRECT PHOTOLYSIS

OH radical induced indirect photolysis of Octopirox can be calculated with US EPA AOPWIN Program estimating low degradation half-lives of 5h (neutral form of Octopirox). Half-life for the reaction with ozone is 48 min. As Octopriox has a low vapour pressure, is water soluble (see IUCLID Section 4.8) and has therefore a low Henry’s Law Constant of 1.1*10-7 Pa*m3/mole (see IUCLID Sections 4.6 & 4.8), volatilisation is not an exposure route which has to be considered.

WATER COMPARTMENT

HYDROLYSIS

Octopirox has no functional groups which could be hydrolyzed under environmental conditions at pH 4-9 (see OECD Guideline 111). But in the dark reaction carried out in the Direct photolysis experiment (see IUCLID Section 5.1.3) Octopriox disapperared at pH 9 with a Half-life of 2.7 d and at pH4 with 12d. This could be interpreted as hydrolysis e.g. ring opening of the heterocycle but the transformation products could not be identified. The half-life of the Direct photolysis (at pH 4 0.2h at 24 deg C, pH 9 0.6h at 27 deg C) is much lower as for hydrolysis in the dark reaction described before.

DIRECT PHOTOLYSIS

Coiffard et al (Pharma Science, 1996, 6, 455 -458) had investigated the direct photolysis of Octopirox at pH7 with spectrometry as analytical method and found rapid transformation. Clariant was interested to carry out the direct photolysis at pH 4 (neutral form of Octopirox) and pH 9 (ionic form of Octopriox) to investigate possible differences. In addition a substance specific analysis with HPLC and LC MS MS was applied to identify also possible metabolites.

Octopirox degrades rapidly by Direct photolysis (OECD 316). The half-life at pH 4, 24 deg C is 0.2 h and at pH 9, 27 deg C 0.6h.

During direct photolysis in water the first metabolite formed is the ring-N deoxygenated Octopirox (NDO). NDO is formed at 0.032 1/h at pH 9 and 1.2 1/h at pH 4. NDO itself is further transformed with a half-life of 16h. After 125h (ca. 5d) of direct photolysis Octopirox was completely disintegrated means no pyridinone chromophore could be detected any more.At pH4 a DOC removal of 31% could be observed during the full period of the photolysis. During direct photolysis other non aromatic metabolites were formed but the structure of these metabolites could not be evaluated. Some hints of possible structures are published in the open literature (Taylor et al, JACS 1961, 83, 4484 -85, Redmond et al. JACS 1996, 118, 10124 -10133).

INDIRECT PHOTOLYSIS

In principle indirect photolysis of Octopirox should also occur not only in air but also in water as OH radicals may be formed from sensitizers like humic acid and sunlight. But it is likely that indirect photolysis in water is slower than direct photolysis.

SOIL COMPARTMENT

DIRECT PHOTOLYSIS ON SOIL SURFACES

As reported in IUCLID SECTION 5.1.3 Octopriox is rapidly degraded by DIRECT Photolysis in water at pH 4 and 9. Direct Photolysis on soil surfaces are carried out similarly to the Direct photolysis in water (see proposed OECD Guideline on 'Phototransformation of Chemicals on Soil surfaces). So it is very likely that Octopirox is also rapidly degraded when photolyzed on soil surfaces.