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Environmental fate & pathways

Hydrolysis

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Description of key information

Hydrolysis half-life at 25°C: 9.3 h at pH 4, 351 h at pH 5.5, 1590 h (66 d) at pH 7, 214 h at pH 8, 24.8 to 31.6 h at pH 9 (OECD 111). The analysis of the experiments at the extremes of pH yielded a calculated value of 73.4 days at pH 7 and 25°C. In the environmental exposure assessment (EUSES 2.1.2) a degradation half-life in water of 73.4 days at 25°C is used. 

Key value for chemical safety assessment

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

Additional information

Hydrolysis half-lives at 25°C of 9.3 h at pH 4, 351 h at pH 5.5, 1590 h (66 d) at pH 7, 214 h at pH 8 and 24.8 - 31.6 h at pH 9 were determined in a reliable study conducted in compliance with GLP. Hydrolysis half-lives at 10°C of 35 h at pH 4, 10000 h at pH 7 and 140 h at pH 9 were determined. Hydrolysis half-lives at 35°C of 4.3 h at pH 4, 590 h at pH 7 and 6.5 h at pH 9 were determined. The analysis of the experiments at the extremes of pH yielded a calculated value of 73.4 days at pH 7 and 25°C, based on the assumption that the hydroxide and hydronium catalysed reactions were the only relevant mechanisms at pH 7 (i.e. k_obs = k_H+*[H+] + k_-OH*[-OH])).

At extremes of pH and under standard hydrolysis test conditions, it is reasonable to suggest that the rate of hydrolysis is dominated by either the hydronium or hydroxide catalysed mechanism.

 

Therefore, at low pH:

kobs≈kH3O+[H3O+]

 

At pH 4 [H3O+] = 10-4mol dm-3and at pH 2 [H3O+] = 10-2mol dm-3; therefore, kobsat pH 2 should be approximately 100 times greater than kobsat pH 4.

 

The half-life of a substance at pH 2 is calculated based on:

t1/2(pH 2) = t1/2(pH 4) / 100

 

The calculated half-life of D5 at pH 2 and 35°C (relevant for conditions in the stomach following oral exposure) is therefore 0.043 hours (approximately 3 minutes).

The hydrolysis half-life of D5 at 35ºC and pH 7 (relevant for lungs and blood) is 590 hours. At 35°C and pH 5.5 (relevant for dermal exposure), the hydrolysis half-life is expected to be between the values for pH 4 (4.3h) and pH 7 (590 h).