O,O,O-triphenyl phosphorothioate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2007-10-16 to 2007-12-10

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

The incubation vials were agitated in water baths at three different temperatures for a maximum of approximately 30 days. After various time intervals, samples were analysed by HPLC-ESI-MS/MS to determine the hydrolysis rates of the test substance. In addition, the samples were analysed by HPLC-UV to detect the formation of phenol for both test substances. The generation of phenol as the final degradation product of the test substance is an indication of the integrity of the hydrolysis process.

Buffers:

- pH: 4
- Type and final molarity of buffer: Citrate buffer
- Composition of buffer: 500 mL of 0.2 M monopotassium citrate were adjusted to pH 4 with 1 M sodium hydroxide solution (NaOH)

- pH: 7
- Type and final molarity of buffer: Phosphate buffer
- Composition of buffer: 500 mL of 0.2 M monopotassium phosphate were adjusted to pH 7 with 1 M sodium hydroxide solution (NaOH)

- pH: 9
- Type and final molarity of buffer: Borate buffer
- Composition of buffer: 500 mL of 0.2 M boric acid (H3BO3) in 0.2 M KCl were adjusted to pH 9 with 1 M sodium hydroxide solution (NaOH)

All buffer solutions were filled up with purified water to give a total volume of 1 L

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: tightly closable incubation vessels with total volume of approx. 14 mL
- Sterilisation method: buffer solutions were filtered sterile and incubation vessels were rinsed with ethanol and dried under UV light prior to usage. At the end of the incubation, sterility tests were performed where hydrolysis occurred. The solutions were filtrated with the sterility test "Sterisart alpha 2000" (Satorius) and incubated with thioglycollate medium and tryptic soy broth medium at 32°C and at room temperature, respectively. Incubation period was 11 days.
- Lighting: no
- If no traps were used, is the test system closed/open: closed

TEST MEDIUM
- Volume used/treatment: 5 mL incubation solution
- Kind and purity of water: purified water
- Preparation of test medium: 2.5 mL of the stock solution of the test substance and the transformation product (19 ng/µL, respectively) were dissolved in buffer solutions to give a total volume of 250 mL of each pH. The resulting test item and transformation product concentrations were 19 pg/µL. .
- Renewal of test solution: no
- Identity and concentration of co-solvent: The concentration of THF in buffer solutions was 1% (v/v)

OTHER TEST CONDITIONS
- Adjustment of pH: no
- Dissolved oxygen: not reported

Number of replicates:

For every temperature (20, 35 and 50°C), three sets of vessels were prepared (pH 4, 7 and 9). Every single set consisted of at least 18 vessels (two for every measuring point)

Positive controls:

no

Negative controls:

no

Transformation products:

yes

No.:

#1

Details on hydrolysis and appearance of transformation product(s):

The first test substance hydrolyses to a major extend under separation of phenol to a transformation product which itself is hydrolsed under further separation of phenol.

The second test substance is another possible transformation product of the first test substance, which is expected to occur at a minor extend without separation of phenol. The expected transformation product is further hydrolyses to another transformation product under separation of phenol.

For the first parent compound, a concentration of 5.2 pg phenol/µL in the incubation solution corresponds to the complete transformation to the first interim transformation product. A concentration of 10.4 pg phenol/µL indicates that also the interim transformation product is completly hydrolysed.

For the expected transformation product, a concentration of 5.5 pg phenol/µL in the incubation solution corresponds to the complete transformation to the first interim transformation product. A concentration of 11.0 pg phenol/µL indicates that also the interim product is completly hydrolysed.

pH:

4

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

115.8 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: calculated; test material

pH:

4

Temp.:

35 °C

Hydrolysis rate constant:

0 h-1

DT50:

60.7 d

Type:

other: slope of trendline equations

Remarks on result:

other: test material

pH:

4

Temp.:

50 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

24.8 d

Type:

other: slope of trendline equations

Remarks on result:

other: test material

pH:

7

Temp.:

25 °C

Hydrolysis rate constant:

0 h-1

DT50:

102.4 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: calculated, test material

pH:

7

Temp.:

35 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

50.2 d

Type:

other: slope of trendline equation

Remarks on result:

other: test material

pH:

7

Temp.:

50 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

18.8 d

Type:

other: slope of trendline equation

Remarks on result:

other: test material

Key result

pH:

9

Temp.:

20 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

31.8 d

Type:

other: slope of trendline equation

Remarks on result:

other: test material

pH:

9

Temp.:

25 °C

Hydrolysis rate constant:

0.001 h-1

DT50:

24.2 d

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other: calculated; test material

pH:

9

Temp.:

35 °C

Hydrolysis rate constant:

0.002 h-1

DT50:

14.5 d

Type:

other: slope of trendline equation

Remarks on result:

other: test material

pH:

9

Temp.:

50 °C

Hydrolysis rate constant:

0.005 h-1

DT50:

5.4 d

Type:

other: slope of trendline equation

Remarks on result:

other: test material

Other kinetic parameters:

Calculated hydrolysis rate constant and dissipation half life of test material
pH 4 (20°C): 0.00018 h-1; 162.6 d
pH 7 (20°C): 0.00019 h-1; 148.8 d
pH 9 (20°C): 0.00085 h-1, 33.9 d

pH 4 (25°C): 0.00025 h-1; 115.8 d
pH 7 (25°C): 0.00028 h-1; 102.4 d
pH 9 (25°C): 0.00120 h-1, 24.2 d

Determined hydrolysis rate constants and half-lifes of the expected transformation product:
pH 4 (20°C): 0.00034 h-1; 84.3 d
pH 4 (35°C): 0.00042 h-1; 69.0 d
pH 4 (50°C): 0.00114 h-1; 25.4 d

pH 7 (20°C): 0.00174 h-1; 16.6 d
pH 7 (35°C): 0.00602 h-1; 4.8 d
pH 7 (50°C): 0.01291 h-1; 2.2 d

pH 9 (20°C): 0.00951 h-1; 3.0 d
pH 9 (35°C): 0.0541 h-1; 0.5 d
pH 9 (50°C): 0.19783 h-1; 0.1 d

Calculated hydrolysis rate constant and dissipation half-life of the expected transformation product:
pH 4 (20°C): 0.0003 h-1; 96.5 d
pH 7 (20°C): 0.00185 h-1; 15.6 d
pH 9 (20°C): 0.00997 h-1; 2.9 d

pH 4 (25°C): 0.0037 h-1; 77.9 d
pH 7 (25°C): 0.00266 h-1; 10.9 d
pH 9 (25°C): 0.01726 h-1; 1.7 d

Details on results:

Within the 30 days of the study phenol concentrations of up to 5.8 pg/µL were found in the first test substance samples (50°C, pH 9). A phenol concentration of 5.2 pg/µL in the incubation solution corresponds to the complete transformation of the test substance to the first main transformation product. Under consideration of the half-life of the first test substance and the proposed hydrolysis pathway (transformation products of the test substance are further hydrolysed under separation of phenol), the phenol concentration found in the incubation solution indicates that the transformation product of the first test substance are hydrolysed in parallel after the beginning of hydolysis of the test substance.

For the second test subtance, a phenol concentration of 5.5 pg/µL in the incubation solution corresponds to the complete transformation of the test substance to the first transformation product. Within the 30 days of the study phenol concentrations of up to 5.8 pg/µL were found in the first test substance samples (35°C, pH 9). Under consideration of the half-life of the second test substance and the proposed hydrolysis pathway (the transformation product of the test substance is further hydrolysed under separation of phenol), the phenol concentration found in the incubation solution indicates that the transformation product of the second test substance is hydrolysed in parallel after the beginning of hydrolysis of the test substance.

Overall, the results indicate that the degradation via hydrolysis of the two test substances and their respective transformation products runs in parallel once hydrolysis has started.

.

Validity criteria fulfilled:

yes

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 2007). 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-triphenyl phosphorothioate 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.