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Environmental fate & pathways

Hydrolysis

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Description of key information

At pH 7 the rate constant was calculated at 1.114E-04 and at pH 9 this was calculated at 3.018E-03.  These rate constants correspond to half lives of 6222 hours and 230 hours at 25 °C and pH 7 and 9, respectively.

Key value for chemical safety assessment

Half-life for hydrolysis:
6 222 h
at the temperature of:
25 °C

Additional information

Two studies with identical experimental setup were carried out to measure the rate of hydrolysis of the test substance. The results of both studies were similar. However, one study (study number AN-ASB 0260) was carried out using test substance with a purity of only 56.3 % and is therefore considered to be of supportive value only. The results presented below are based on study AN-ASB 0248 which is considered to be the key study.

The hydrolysis rate for the test substance was determined in accordance with EU method C.7, and in accordance with GLP. The test substance was assessed at a concentration of 1 g/L in all parts of the study. HPLC was used to analyse the test substance throughout. A preliminary test was carried out to assess the rate of hydrolysis at pH 4, 7 and 9 at 50 °C and as a result in accordance with the guidelines further testing was not carried out at pH 4.

The main test was carried out at pH 7 and 9 at 50 °C initially. A linear dependence on the time of degradation and the logarithm to base ten of the test item concentration was obtained which means that the hydrolysis reaction was a pseudo first order reaction. Therefore, further tests were carried out at pH 7 at 60 and 70 °C and pH 9 at 38 °C. From the measured results the rate constants and the half-lives of the test substance were calculated at:

pH 7, 50 °C: k = 0.0037 h-1, DT50 = 186 hours

pH 7, 60 °C: k = 0.136 h-1, DT50 = 51 hours

pH 7, 70 °C: k = 0.0431 h-1, DT50 = 16 hours

pH 9, 50 °C: k = 0.0872 4 h-1, DT50 = 8 hours

pH 9, 38 °C: k = 0.0186 h-1, DT50 = 37 hours.

The Arrhenius equation was used to calculate the rate constant at 25 °C. At pH 7 this was calculated at 1.114 ×10-4 h-1, and at pH 9 at 3.018 × 10-3 h-1. These rate constants were used to estimate the half-lives of 6222 hours and 230 hours at pH 7 and 9, respectively.