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Environmental fate & pathways

Hydrolysis

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Description of key information

The half-life of the parent compound (O,O,O-triphenyl thiophosphate) at 25°C was determined to be 24.2 days (pH 9), 102.4 days (pH 7) and 115.8 days (pH 4). 
It can be assumed that the transformation products of the test substances are further hydrolysed under separation of phenol.

Key value for chemical safety assessment

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

Additional information

A hydrolysis study based on OECD 111 was performed to examine the hydrolysis behaviour of the test substance and the assumed transformation product at pH values normally found in the environment (Ciba specialty Chemicals Inc, 2007): pH 4 - 9. After up to 30 days of incubation, the half-life of the parent compound (O,O,O-triphenyl thiophosphate) at 25°C was determined to be 24.2 days (pH 9), 102.4 days (pH 7) and 115.8 days (pH 4). After up to 30 days of incubation, the half-life of the expected transformation product (triphenyl phosphate) at 25°C was determined to be 1.7 days (pH 9), 10.9 days (pH 7) and 77.9 days (pH 4).

In addition, investigation on the formation of phenol, which is generated during the hydrolysis process of each of the two test substances, was made. For the parent compound, a concentration of 5.2 pg phenol/µL in the incubation solution corresponds to the complete transformation of the parent compound to diphenyl thiophosphate.

For the tested transformation product, a concentration of 5.5 pg phenol/µL in the incubation solution corresponds to the complete transformation of the transformation product to a further interim transformation product diphenyl phosphate.

In the incubation solutions of the parent compound and in the incubation solution of the transformation product, phenol concentrations of up to 5.8 pg phenol/µL each were measured.

Under consideration of the half-life of the respective test substances (O,O,O-triphenyl thiophosphate and triphenyl phosphate) and the proposed hydrolysis pathway (transformation products of the test substances are further hydrolysed under separation of phenol), the phenol concentrations found in the incubation solution indicate that the transformation products of the respective test substances are hydrolysed in parallel once hydrolysis of the test substance has started.

However, it can be expected that the abiotic transformation in water of O,O,O-triphenyl thiophosphate to triphenyl phosphate takes place to a minor extent as the hydrolysis half lives of the triphenyl phosphate are much lower than the half-lives of triphenyl thiophosphate. 

A supporting hydrolysis study with O,O,O-triphenylphosphorotioate in a lower purity is available (Ciba 1998). As the substance consists of several structural similar constituents an indirect method was used to measure the hydrolytic behavior via phenol formation. The concentration of 3.4g/L was tested. After 5 days the decomposition at different pH values (4, 7, 9) at 50°C was below 1%. The hydrolysis of the single constituents was not analysed separately. No additional vehicle was used. With respect to the limited solubility of O,O,O- triphenyl thiophosphate the test concentration of 3.4 g/L might have been too high and the method not sensitive enough to measure degradation. Therefore, this result is not considered to be contradictory to the result of the key study.