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Description of key information

The DT50 at 25°C and pH 7 of 332 days will be used in the assessment.

Key value for chemical safety assessment

Half-life for hydrolysis:
332 d
at the temperature of:
25 °C

Additional information

One GLP-compliant study was available in which the rate of hydrolysis of delta-damascone as a function of pH was determined (Huntingdon Life Sciences Ltd., 2009a). The study was performed in accordance with OECD Guideline 111.

The preliminary study showed that at pH 4 and 50 ± 0.5 °C, less than 10% hydrolysis had occurred after 120 hours (5 days), equivalent to a half-life of greater than 1 year under environmental conditions (25 °C). No further testing was therefore necessary at this pH value.

At pH 7 and pH 9 and 50 ± 0.5 °C, however, greater than 10% hydrolysis had occurred after 120 hours (5 days), but less than 50% hydrolysis after 2.4 hours, indicating an environmental half-life (DT50) of between 1 day and 1 year. This necessitated proceeding to the next stage of testing at these pH values. The hydrolysis reaction for delta-damascone at pH 7 and pH 9 was shown to follow pseudo-first order behaviour.

A third test was then conducted at pH 7 and pH 9 at elevated temperatures of 60 and 70 °C, and the hydrolysis rate constant (k) and DT50 at 25 °C were extrapolated from the measured values of log10k at elevated temperatures using the Arrhenius relationship. At pH 7 and pH 9, respectively, DT50 values of 332 and 41 days were obtained.

Delta-damascone was determined to be hydrolytically stable under acidic conditions, but to hydrolyse under neutral and basic conditions. The half-life at 25°C and pH 7 of 332 days, with a corresponding degradation rate constant of 7.38E-04 d-1 will be used in the assessment.


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