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Environmental fate & pathways

Hydrolysis

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Description of key information

In the preliminary study, the results indicate that a 25°C, Amber core (P-#620) possesses a half-life between 1 day and 1 year at pH 4, 7 and 9. This indicated the need for further testing at pHs 4, 7 and 9 using the extended tests as described in the Directive. In the definitive study, the hydrolysis reaction of Amber core at 25°C and pH 4 occurred with a half-life time of 216 hours (9 days). At pH 7 and 25°C, the hydrolysis reaction of Amber core occurred with an estimated half-life time of 648 hours (27 days) and at pH 9 and 25°C, an estimated half-life time of 609 hours (25 days). To consider the worst case, the half-life for hydrolysis used as key value for chemical safety assessment was the greatest half-life obtained: 648 hours, equivalent to 27 days at 25°C and pH 7.

Key value for chemical safety assessment

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

Additional information

Two valid studies according to the Directive 84/449/EEC Part C Method C.07, performed under GLP are available to assess the abiotic degradation of Amber core (P-#620). The results of the preliminary study (supporting study) were provided in the first report (Sunakawa, 1992). Then, the definitive study (key study) was performed and the results were provided in the second report (Sunakawa, 1994).

In the preliminary study (Sunakawa, 1992), hydrolysis was evaluated over 5 days at 50°C in aqueous solution at pH 4, 7 and 9. Under the test conditions, P-#620 was found to undergo hydrolysis at all pH values investigated. The results indicate that a 25°C, P-#620 possesses a half-life between 1 day and 1 year at pH 4, 7 and 9. This indicated the need for further testing at pHs 4, 7 and 9 using the extended tests as described in the Directive.

For the definitive study (Sunakawa, 1994), Test 1 was performed to determine the order of the hydrolysis reaction at each pH. The concentration of test substance in each buffer at 50°C was monitored over 47 hours and a plot of log10(concentration) versus time was prepared. At pH 4 this plot was found to produce a straight line, indicating pseudo-first order behaviour. Accurate determination of half-life and rate constant were then performed according to Test 3. At pHs 7 and 9, the plot did not produce a straight line, indicating non-pseudo first order behaviour. Test 2 was therefore performed and estimated values of half-life and rate constant were calculated. In Test 3 (pH 4 buffer) hydrolysis was examined by monitoring the test substance concentration over periods of 21 hours at 60°C and 10 hours at 70°C. A plot of log10(observed rate constant) against reciprocal temperature (in degrees Kelvin) was then prepared and the plot extrapolated to 25°C. At 25°C and pH 4, a half-life of 216 hours (9 days) and a rate constant of 3.21 x 10-3hours-1were calculated. In Test 2 (pH 7 and 9 buffers) hydrolysis was examined by monitoring the test substance concentration over periods of 24 hours at 60°C and 9 hours at 70°C. For each pH, a plot of log10(observed rate constant) against reciprocal temperature (in degrees Kelvin) was prepared and extrapolated to 25°C. At 25°C and pH 7, an estimated half-life of 648 hours (27 days) and an estimated rate constant of 1.07 x 10-3hours-1were determined. At 25°C and pH 9, an estimated half-life of 609 hours (ca 25 days) and an estimated constant of 1.14 x 10-3hours-1were determined.

Taking the longest half-life for hydrolysis into consideration, the half-life of 648 hours, equivalent to 27 days at 25°C and pH 7 was used as the key value for chemical safety assessment.