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Hydrolysis

Description of key information

OECD Guideline 111, GLP, key study, validity 2:
25°C, pH 4: T1/2 = 162 days, percentage remaining after 30 days = 88.3%; 
25°C, pH 7: T1/2 = 179 days, percentage remaining after 30 days = 87.6%; 
25°C, pH 9: T1/2 = 150 days, percentage remaining after 30 days = 87.7%; 
37°C, pH 1.2: No significant hydrolysis after 24 hours.

Key value for chemical safety assessment

Half-life for hydrolysis:

179 d

at the temperature of:

25 °C

Additional information

One key study is available to assess the hydrolysis potential of the test substance. This study was performed according to OECD Guideline 111 with GLP statement.

During Preliminary study, initial sample results were all lower than the 'weighed in' concentration which also suggested some degradation, volatilisation or interaction of the test material occurred before the samples were incubated at the test temperatures. Therefore, it was decided to not perform the usual testing at a range of temperatures and extrapolate to give results at 25°C, but to perform the test directly at 25°C for 30 days. This was also to reduce the possibility of other interactions occurring. A further step taken was to silanize the test vessels to minimize adsorption/interaction with any active sites on the glass surface. A 30 day test period was considered long enough to replicate what would happen in the environment.

The graphs of Log10 concentration versus time for the 25°C tests showed no significant signs of second order behaviour. Although timepoints were still variable, even between duplicate samples at a given timepoint, an overall trend in reduction of concentration was evident. As discussed above, it was possibly not only hydrolysis occurring, the overall result was therefore taken from the percentage remaining after 30 days at 25°C. Although this does not give a rate constant, it still provides an indication as to the persistence of the test material in the environment.

Some timepoint values were omitted from the calculations as they were considered erroneous. Several samples appeared to have reduced in concentration somewhat more than was expected from the general trend and the replicate timepoint sample. This was further evidence that additional degradation, volatilisation or interaction was occurring besides hydrolysis.

It was considered that the analytical method was not the cause of the variable sample results as it proved to be a reliable and robust method throughout the course of the test. The standards had consistent areas and duplicates corrected up closely throughout testing.

No significant peaks were observed around the retention time of the test material on analysis of any matrix blank solutions.

The percentage remaining after 30 days at 25°C of the test material were 88.3 %, 87.6 % and 87.7 % at the pH values of 4, 7 and 9 respectively. The corresponding half-lives were 162 days, 179 days and 150 days at the pH values of 4, 7 and 9 respectively. Under the physiologically relevant conditions of pH 1.2, 37.0 ± 0.5 °C, the test material was determined not to show significant hydrolysis after 24 hours.