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Phototransformation in water

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The direct photolysis of the two isomers of 2-amylanthraquinone was evaluated in a study according to the OECD 316 guideline. A tiered approach was followed.

Tier 1 consisted of the recording of UV absorption spectra at pH 4, 7 and 9. For 10 mg/L solutions of 2-amylanthraquinone, the calculated latitudinal and seasonal values of (kp)max and (t½)min were notably different between pH 4 and pHs 7 and 9. The (t½)min values calculated for pH 4 were predominantly faster than for those observed for pH 7 and 9. Based on these results the definitive photolysis test was carried out at a pH of 7 only. In the Tier 2 test, the direct photolysis rate in water was determined in a Heraeus Suntest Solar Simulator. Photolytic degradation rates were corrected with results from a dark control test. Analyses were carried out with HPLC-UV. LC-MS was used for confirmation of the identity of the parent compounds and for determination of transformation products.

The photolytic half-life times that were determined in the laboratory were 21 minutes for the isomer 2-amylanthraquinone (A) and 2.7 minutes for the isomere 2-amylanthraquinone (B). Based on these results, predicted photolytic half-life times in the environment were calculated:

For 2-amylanthraquinone (A) the predicted environmental photolytic half-life varies between 1123 days at 30ºN in the summer and 20027 days at 60ºN in the winter.

For 2-amylanthraquinone (B) the predicted environmental photolytic half-life varies between 148 days at 30ºN in the summer and 2595 days at 60ºN in the winter.

The environmental photolytical half-life times are so high that photolysis is not assumed to be a relevant degradation process in the environment.

From the analysis of the stock solutions via LC/MS it was proposed that the peaks annotated as 2-amylanthraquinone (A) and 2-amylanthraquinone (B) during Tier 2 correspond to the isomers (2-(3-methylbutan-2-yl)anthracene-9,10-dione) and (2-(2-methylbutan-2-yl) anthracene-9,10-dione), respectively. A third isomer has also been proposed to be present, 2-(2-(2,2-dimethylpropyl)anthracene-9,10-dione.

The photolytic degradation of 2-amylanthraquinone produced at least six transformation products with regions of interest in the HPLC/UV chromatograms. No transformation product regions of interest were successfully identified via LC/MS due to low initial concentrations, solubility and the number of transformation products that were separated during the analytical run. The OECD 316 guideline recommends that the test is performed at less than one half the water solubility of the test compound; when the decision was made to carry out additional ID work at a higher concentration than that of the guideline no discernible differences were noted. As only one wavelength of detection was used for the detection of the generated samples there may have been more than six transformation products formed during irradiation. All transformation products observed appear to be short lived and transitory indicating that over time the residual related compounds were likely to be a mixture of many complex compounds.

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