2-amino-6-methyl-4-propyl-1,2,4-triazolo[1,5-a]pyrimidin-5(4H)-one

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

other: Non-GLP, available as unpublished report, minor restrictions in design and/or reporting but otherwise adequate for assessment

Study type:

direct photolysis

Qualifier:

no guideline followed

Principles of method if other than guideline:

The stability of low (5ppm) and high (500ppm) concentration solutions of the test substance in water, in a dilute solution of ‘Gramoxone’ in water and in a dilute solution of acetone in water; exposed to sunlight at prevailing ambient temperatures was investigated.

GLP compliance:

no

Radiolabelling:

yes

Analytical method:

other: Chromatography was carried out on precoated 0.25mm layers of silica gel and Quantitative measurements were performed with radioscans of radioactive areas on chromatograms

Details on sampling:

Sub-samples of the solution (15mL) were withdrawn at 0, 1, 2, 4, 7, 14, and 27 days after the addition of the radioactivity. The subsamples were stored at -15°C until required for analysis.

Light source:

sunlight

Details on light source:

Weather conditions: This experiment was conducted between 22/5/76 and 6/8/76 in the open air. The general conditions were very hot with a great deal of direct sunlight.

Details on test conditions:

STOCK SOLUTION:
A stock solution was prepared containing 48.5 µCi of the C14-radioactive labeled test substance (1.41 mCi/mM) in 10 mL of methanol (i.e. 7.14 mg of substance in 10 mL).

TEST SOLUTIONS:
Portions of distilled water, a 1% solution of ‘Gramoxome U.K.’ in water and a 4% solution of acetone in water (250mL) were each treated with 1.75 mL of the labelled test substance solution to give 5 ppm solutions. The 500 ppm solution of the test substance was made with unlabelled test substance (120.7 mg) in methanol (5mL) in a 4% solution of acetone in water. he solutions were placed in 15cm crystallizing dishes and covered with polythene. The dishes were placed outside and exposed to sunlight from 22/5/1976 for up to 77 days.

As a control experiment 10µCi of 14C-diquat (compound II) of specific activity 29mCi/mM was dissolved in water with dry diquat dibromide (2.26 mg) to give the 5 ppm diquat ion solution.

The following solutions were used:
- Solution 1: 5ppm solution of labelled 14C-test substance in distilled water
- Solution 2: 5 ppm solution of labelled 14C-test substance in 1% ‘Gramoxone U.K. formulation’ in water
- Solution 3: 5ppm solution of labelled 14C-test substance in a 4% acetone-water solution.
- Solution 4: 500 ppm solution of unlabelled test substance in a 4% acetone water solution*
- Solution 5: 5 ppm 14C-diquat solution in water.
*Solution 4 provided a source of larger quantities of the degradation products. It has not been fully analyzed.

WEATHER CONDITIONS:
The general conditions were very hot with a great deal of direct sunlight.

Reference substance:

yes

DT50:

ca. 4 d

Transformation products:

yes

Details on results:

ANALYSIS OF SOLUTIONS:
See 'Any other information on results incl. tables:
Although the results are variable, solutions 2 and 3 show the same trend of increases as the diquat solution; this may well be explained by concentration of the solution by evaporation during the experiment. The increase is of a similar order to that obtained with the diquat solution. The autoradiograms of the chromatograms of the aqueous solutions showed a rapid and comprehensive breakdown of the test substance, consequently a more intensive examination of the solution was undertaken.

ION-EXCLUSION CHROMATOGRAPHY OF THE SOLUTIONS:
See 'Any other information on results incl. tables:
The solutions were chromatographed on Amberlite XAD-2 resin. Autoradiograms of these chromatograms of the methanol eluates shows that the pattern of breakdown for each solution differs. For solution 2, the difference may be due to the presence of the coloured ‘Gramoxone’ and acetone could act as a photosensitizer in solution 3. However, the rate of photo degradation appeared to differ little between the solutions. In solution 1 and 3, compound 5 is the major product but in solution 2, compound 6 appears to be the major product. This compound is unusual in that it is less polar than the test substance. There are numerous minor degradation products more polar than the parent in all the solutions.

Results with reference substance:

The 14C-diquat solution was sampled and analyzed as described. An autoradiogram of the samples reveals that the photo degradation proceeded smoothly throughout the period of the experiment. This suggests that no unexpected variables affected the photo degradation of the test substance solutions during the course of this study.

The radioactivity in test substance solutions expressed as a percentage of the calculated added activity (7.53E+04 dpm/mL):

solution	Percentage of added radioactivity at times (in days)
	0	1	2	4	7	14	27
5ppm solution of labelled 14C-test substance in distilled water	102	96	92	87	86	96	89
5 ppm solution of labelled 14C-test substance in 1% ‘Gramoxone U.K. formulation’ in water	*	86	94	87	95	109	115
5ppm solution of labelled 14C-test substance in a 4% acetone-water solution	95	94	99	107	117	124	No sample

 *spurious result

The percentage of radioactivity obtained in fractions from the XAD-2 chromatography of the C14 labelled test substance photodegradation solutions.

Solution	1	1	1	1	1	2	2	2	2	2	2	3	3	3	3	3	3
day	0	2	7	14	27	0	1	4	7	14	27	0	1	2	4	7	14
% in aqueous portion	0	7	9	8	8	0	0	4	7	6	16	0	1	3	4	6	11
% in methanol soln 1*	100	90	87	85	75	100	100	96	90	92	81	100	99	95	95	92	88
% in methanol Soln 2 onwards	0	4	4	7	17	0	0	0	3	2	3	0	0	2	2	2	2
Approx. percentage of original activity recovered	91	81	81	82	102	100	100	89	76	81	68	113	102	95	93	88	93

* Solutions labelled ‘Methanol solution1’ were concentrated in vacuo and chromatographed; these fractions contained an average of ca. 75% of the original radioactivity applied to the column.

Validity criteria fulfilled:

not applicable

Conclusions:

The results show that aqueous solutions of the test substance are readily photodegradable in bright sunlight. The rate of degradation was rapid with half life of approximately 4 days. In the presence of ‘Gramoxone’ the degradation pattern changed but the rate of decay of the test substance was unchanged.

Executive summary:

The stability of low (5ppm) and high (500ppm) concentration solutions of the test substance in water, in a dilute solution of ‘Gramoxone’ in water and in a dilute solution of acetone in water; exposed to sunlight at prevailing ambient temperatures was investigated. The following solutions were used to determine the photodegradability: solution1: 5ppm solution of labelled 14C-test substance in distilled water, solution 2: 5 ppm solution of labelled 14C-test substance in 1% ‘Gramoxone U.K. formulation’ in water,solution 3: 5ppm solution of labelled 14C-test substance in a 4% acetone-water solution, solution 4: 500 ppm solution of unlabelled test substance in a 4% acetone water solution, and solution 5: 5 ppm 14C-diquat solution in water. The results show that aqueous solutions of the test substance are readily photodegradable in bright sunlight. The rate of degradation was rapid with half life of approximately 4 days. In the presence of ‘Gramoxone’ the degradation pattern changed but the rate of decay of the test substance was unchanged.

Description of key information

The rate of degradation was rapid with half life of approximately 4 days.

Key value for chemical safety assessment

Half-life in water:

4 d

Additional information

The stability of low (5ppm) and high (500ppm) concentration solutions of the test substance in water, in a dilute solution of ‘Gramoxone’ in water and in a dilute solution of acetone in water; exposed to sunlight at prevailing ambient temperatures was investigated. The following solutions were used to determine the photodegradability: solution1: 5ppm solution of labelled 14C-test substance in distilled water, solution 2: 5 ppm solution of labelled 14C-test substance in 1% ‘Gramoxone U.K. formulation’ in water, solution 3: 5ppm solution of labelled 14C-test substance in a 4% acetone-water solution, solution 4: 500 ppm solution of unlabelled test substance in a 4% acetone water solution, and solution 5: 5 ppm 14C-diquat solution in water. The results show that aqueous solutions of the test substance are readily photodegradable in bright sunlight. The rate of degradation was rapid with half-life of approximately 4 days. In the presence of ‘Gramoxone’ the degradation pattern changed but the rate of decay of the test substance was unchanged.