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Environmental fate & pathways

Phototransformation in water

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In deionised water the half-life times were 9.2 days at 10 mg/L and 9.6 days at 32 mg/L, and in OECD nutrient medium a half-life time of 3.2 days at 10 mg/L and 7.7 days at 32 mg/L was obtained. The longer half-life time obtained in the tests at the concentration of 32 mg/l in the presence of light may be due to hindered radiation of the molecules of the substance, as the solution was dark coloured.

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Additional information

The stability of the substance in aqueous test solutions was investigated.

The tests were performed in order to examine the stability under conditions simulating those in the environment (pH 7, presence of light and air). Under these conditions, chemicals may be exposed to abiotic degradation by several chemical and physical processes, e.g. hydrolysis, oxidation and photolysis. Test 1 was performed under these conditions in pure water at a temperature of 21°C at two concentrations. Under the same conditions, but in the dark, test solutions at the same concentrations were performed to serve as controls. Additionally, naturally occurring traces of inorganic compounds may influence the chemical stability of the test substance in the environment. Test 2 was performed at two concentrations in an algae nutrient medium containing traces of salts. Conditions for radiation, ventilation and nutrient medium corresponding those conditions used in ecotox testing in accordance with Commission Regulation (EC) No 761/2009 amending Regulation No 440/2008, Method C.3 ‘Freshwater Alga and Cyanobacteria, Growth inhibition test’ (2009) which is equivalent to OECD Guideline for Testing of Chemicals No. 201 (2006) ‘Alga, Growth Inhibition Test’. The substance is a dark coloured test substance, which reduce the light emission for the algae cells because of shading effects. Enough light is essential for the growth of the algae, so for a reduction of shading effects, the test was carried out with strong photon flow density (110-140 µE x m-2 x s-1; measured in the range 400 to 700 nm) and with a reduced test volume of 25 ml in 300 mL Erlenmeyer flasks. Under the same conditions, but in the dark, test solutions at the same concentrations were analysed to serve as controls. The samples were analysed using a HPLC method with UV detection. The degradation of the investigated test substance can be described by first order kinetics. Half-life times and degradation rates of the substance were calculated from the degradation curves.

The results of the test series in different media clearly indicate that the substance is photolytically unstable in the presence of light. By comparison, the results of the test series conducted in the dark show stability of the test substance under exposure conditions. When performing the tests in pure water (test 1), the half-life times were 9.2 and 9.6 days. In test 2, a nutrient-enriched medium containing salts was taken to examine the stability. In comparison to test 1, catalytic processes might reduce the stability of the substance to a half-life time of 3.2 and 7.7 days. The longer half-life time obtained in the tests at the concentration of 32 mg/l in the presence of light may be due to hindered radiation of the molecules of the substance, as the substance is a dark coloured substance. In conclusion, it is clearly demonstrated, that the substance is rapidly degradable by photolysis. As no additional peaks are shown in the chromatograms transformation products were not detected via HPLC. Due to the complex nature of photochemical processes with a large number of possible transformation pathways, and sub-sequent reactions of produced intermediate species, confirms the difficulty on identification of transformation products.