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Environmental fate & pathways

Hydrolysis

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Description of key information

Sárvári, 2010a, was selected as the key information for this endpoint as it was conducted according to the OECD 111 guideline with a supporting preliminary study and was the most recent study available. Based upon the study guideline, date of the study report and depth of reporting the study was awarded the reliability score of 1 according to the criteria of Klimisch et al, 1997.
Although the registered substance was found to be almost stable at pH 7, hydrolysis was observed at pH 4 and 9 and hydrolysis rate was directly related to a rise in temperature.
Half-lives were reported between 141 hours at 67 ºC and 9136 hours at 25 ºC for test solutions at pH 4, and between 114 hours at 67 ºC and 20546 hours at 25 ºC for test solutions at pH 9.

Key value for chemical safety assessment

Additional information

The key information for hydrolysis is taken from the definitive study of Sárvári, 2010a, which reported (pseudo-)first order half-lives in water as follows:

pH Temp. Hydrolysis rate constant Half-life Remarks (e.g. regression equation, r², DT90)
4 25 °C 0.000076 h-1 9136 h 1/T, 1/K: 0.003354; 1n k: -9.487
4 50 °C 0.00104 h-1 669 h regr. coefficient: 0.9504
4 67 °C 0.00492 h-1 141 h regr. coefficient: 0.9869
9 25 °C 0.000034 h-1 20546 h 1/T, 1/k: 0.003354; 1n k: -10.30
9 50 °C 0.00087 h-1 794 h regr. coefficient: 0.9515
9 67 °C 0.00607 h-1 114 h regr. coefficient: 0.9672

These definitive results were based upon the findings of the preliminary study (Sárvári, 2010b) which reported the need for the definitive study and the following results:

pH Sampling time, hour Concentration of Test Item, µg/ml  Measured pH
Results of the separate test vessels Mean with the 95% cionfidence intervals End/Start, %
4 0 (Start) Control buffer - 4.02
226.7 228.5 ± 3.8 - 4.04
224.3
231
231.6
229
120 Control buffer - 4.01
187.7 178.9 ± 8.7 78 4.06
182
179.2
176.9
168.6
7 0 (Start) Control buffer - 7
136 136.9 ± 1.7 - 6.99
135.3
136.8
138.7
137.8
120 Control buffer - 7
134 134.2 ± 6.7 98 6.99
139
137.1
126.7
not reported
9 0 (Start) Control buffer - 8.99
199.1 202.3 ± 3.4 - 9
201
205.7
204.6
200.9
120 Control buffer - 9
173.7 172.5 ± 3.4 85 9.01
174.8
167.7
173.3
172.9

A large amount of supporting information is available for this endpoint. The results of these additional studies are summarised below:

Source Temperature (ºC) pH Hydrolysis result
rate constant Half life
Anon, 1984 25 5   531 days (zero order kinetics) 1062 days (first order kinetics)
7   1883 days (zero order kinetics) 1867 days (first order kinetics)
9   3436 days (zero order kinetics) 3352 days (first order kinetics)
45 5   208 days (zero order kinetics) 161 days (first order kinetics)
7   202 days (zero order kinetics) 173 days (first order kinetics)
9   169 days (zero order kinetics) 137 days (first order kinetics)
Ehrenberg et al, 1974 20 7 0.000006 hours 14 years (order not reported)
37 7 0.000076 hours  
Vogel & Reinhard, 1986 25 7.5 8.9 seconds 2.5 years (95% CI 2.2-2.8) (order not reported)
Haag & Mill, 1988 25 7.5   1000 days (order not reported)
Hine & Langford, 1956 No values reported.
Weintraub et al, 1986 15     2.2 years (order not reported)
22     1.5-2 years (order not reported)
Jungclaus & Cohen, 1986 15     15 years (order not reported)
20     8 years (order not reported)