[(9-oxo-9H-thioxanthen-2-yl)oxy]acetic acid

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

12 Nov 2018 to 17 Dec 2018

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Version / remarks:

March 04, 2016

Deviations:

no

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

April 13, 2004

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.2120 (Hydrolysis of Parent and Degradates as a Function of pH at 25°C)

Version / remarks:

October 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Appearance: Yellow powder
Purity/Composition: 98.25%
Test item storage: At room temperature protected from light desiccated

Radiolabelling:

no

Analytical monitoring:

no

Buffers:

Acetate buffer pH 4, 0.1 M:
Solution of 16.7% 0.1 M sodium acetate in water and 83.3% 0.1 M acetic acid in water. Buffer contained 0.0009% (w/v) sodium azide.

Phosphate buffer pH 7, 0.1 M:
Solution of 0.1 M potassium di-hydrogen-phosphate in water adjusted to pH 7 using 10N sodium hydroxide. Buffer contained 0.0009% (w/v) sodium azide.

Borate buffer pH 9, 0.1 M:
Solution of 0.1 M boric acid in water and 0.1 M potassium chloride in water adjusted to pH 9 using 10N sodium hydroxide. Buffer contained 0.0009% (w/v) sodium azide.

Details on test conditions:

Preliminary Test - Tier 1
The buffer solutions were filter-sterilised through a 0.2 µm FP 30/0.2 CA-S filter (Whatman, Dassel, Germany) and transferred into a sterile vessel. To exclude oxygen, nitrogen gas was purged through the solution for 5 minutes. The test item was spiked to the solutions at a target concentration of 2 mg/L using a spiking solution in DMSO. For each sampling time, duplicate sterile vessels under vacuum were filled with 6 mL test solution and placed in the dark in a temperature controlled environment at 50.1°C ± 0.1°C.

The spiking volume was < 1% of the sample volume. Nominal concentrations were not corrected for the spiking volume.

The concentration of the test item in the test samples was determined immediately after preparation (t=0), after 2.4 hours and after 5 days. The samples taken at t=2.4 hours and at t=5 days were cooled to room temperature using running tap water.

Analysis was performed on sub-samples of 800 µL. The samples were diluted in a 4:1 (v:v) ratio with 1% formic acid in acetonitrile and analyzed.

Blank buffer solutions containing a similar content of blank spiking solution were treated similarly as the test samples and analyzed at t=0.

The pH of each of the test solutions (except for the blanks) was determined at each sampling time.

Duration:

5 d

pH:

4

Remarks:

pH 7 and 9 were also tested.

Positive controls:

no

Negative controls:

no

Preliminary study:

The analytical results of the preliminary test are given in Table 10 and Table 11.

At pH 4, pH 7 and pH 9, a degree of hydrolysis of < 10% was observed after 5 days. It demonstrated that the half-life time of the test item at 25°C is > 1 year. According to the guideline, no further tests were required.

No test item was detected in the blank buffer solutions at pH 4 and pH 7. A small response at the retention time of the test item was detected in one of the chromatograms of the blank buffer pH 9 solutions. It was considered not to impact the study since the response was very small and the response was not observed in the duplicate study sample.

The mean recoveries of the of the test item containing buffer solutions at t=0 fell within the criterion range of 90-110%. It demonstrated that the analytical method was adequate to support the hydrolysis study on the test item.

Test performance:

At each pH value a degree of hydrolysis of < 10% was observed after 5 days. According to the guideline, performance of the main study (Tier 2) was not required.

Transformation products:

not specified

% Recovery:

> 100

pH:

4

Temp.:

25 °C

Duration:

5 d

Remarks on result:

hydrolytically stable based on preliminary test

% Recovery:

> 100

pH:

7

Temp.:

25 °C

Duration:

5 d

Remarks on result:

hydrolytically stable based on preliminary test

% Recovery:

> 100

pH:

9

Temp.:

25 °C

Duration:

5 d

Remarks on result:

hydrolytically stable based on preliminary test

Key result

Remarks on result:

other: At each pH value a degree of hydrolysis of < 10% was observed after 5 days. According to the guideline, performance of the main study (Tier 2) was not required.

Table 10       

Preliminary Test:  Hydrolysis of the Test Item at pH 4, pH 7 and pH 9

pH code	Sampling time	Analyzed concentration [mg/L]	Degree of hydrolysis [%]		pH
			Individual	Mean
pH 4	0 hours	2.05			4.0
		2.06			4.0
	2.4 hours	2.06	0.12	0.23	4.0
		2.05	0.34		4.0
	5 days	1.99	3.1	3.4	4.0
		1.98	3.7		4.0
pH 7	0 hours	2.13			7.1
		2.13			7.1
	2.4 hours	2.13	-0.098	-0.10	7.2
		2.13	-0.11		7.2
	5 days	2.1	1.1	0.97	7.1
		2.11	0.84		7.1
pH 9	0 hours	2.12			9.0
		2.11			9.0
	2.4 hours	2.12	-0.33	-0.36	9.0
		2.12	-0.40		9.0
	5 days	2.1	0.56	0.46	8.9
		2.11	0.36		8.9

Table 11       

Preliminary Test:  Recoveries

pH code	Nominal concentration [mg/L]	Analyzed concentration [mg/L]	Recovery [%]
			Individual	Mean
pH 4	2	2.05	103	103
	2	2.06	103
pH 7	2	2.13	106	106
	2	2.13	106
pH 9	2	2.12	106	106
	2	2.11	106

Validity criteria fulfilled:

yes

Conclusions:

The preliminary test (Tier 1) was performed for the determination of the rate of hydrolysis of CMTX 2-carboxymethyloxy-thioxanthone at pH values normally found in the environment (pH 4-9).
At each pH value a degree of hydrolysis of < 10% was observed after 5 days. According to the guideline, performance of the main study (Tier 2) was not required.

Executive summary:

In this guideline (OECD 111) study conducted with GLP certification, the test material (EC 282-803-8) was determined to have be hydrolytically stable at pH 4, 7 and 9 after 5 days. Thus a Tier 2 study was not required and the test item is stable to hydrolysis.

Description of key information

Study conducted to recognised testing guidelines with GLP certification.

Key value for chemical safety assessment

Half-life for hydrolysis:

1 yr

at the temperature of:

25 °C

Additional information

Test item is hydrolytically stable at pH 4, 7 and 9 at 25 °C.