Simazine

Hydrolysis

Administrative data

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

7 July 1993 - 28 September 1994

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Deviations:

not specified

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

Simazine

EC Number:

204-535-2

EC Name:

Simazine

Cas Number:

122-34-9

Molecular formula:

C7H12ClN5

IUPAC Name:

6-chloro-N2,N4-diethyl-1,3,5-triazine-2,4-diamine

Test material form:

solid: particulate/powder

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Test material: Simazine (pure)
- Appearance: White powder
- Batch No.of test material: Ref 766
- Expiration date of the batch: Two years from date of manufacture
- Purity: 99.5%

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material: In the dark at 4°C

Radiolabelling:

no

Study design

Analytical monitoring:

yes

Details on sampling:

A 5 mL aliquot of the collected test solution or blank was transferred to a 25 mL volumetric flask and made to volume with mobile phase. The diluted solution was analysed by HPLC.

In the preliminary test, samples were taken at 0 hours, 2.4 hours and 5 days.

Aliquots were removed at t = 0 hours and various time points between 20 and 70% hydrolysis at 50°C for test 1.

Aliquots were removed at three time points, two of which where greater than 30% hydrolysis had occurred (both at 60°C and 70°C) for test 3.

Buffers:

- pH: 5
- Type and final molarity of buffer: 0.1 M
- Composition of buffer: Potassium hydrogen phthalate (ca 20 g) was dissolved in distilled water (1 L). The pH was adjusted to 5.00 with 0.1 M sodium hydroxide solution.

- pH: 7
- Type and final molarity of buffer: 0.1 M
- Composition of buffer: Potassium dihydrogen orthophosphate (13.59 g) was dissolved in distilled water (1 L). The pH was adjusted to 7.00 with 0.1 M sodium hydroxide solution.

- pH: 9
- Type and final molarity of buffer: 0.1 M
- Composition of buffer: Potassium chloride (7.46 g) and boric acid (6.21 g) were dissolved in distilled water (1 L). The pH was adjusted to 8.98 with 0.1 M sodium hydroxide solution.

Details on test conditions:

PRELIMINARY TEST:

Six 100 mL pre-calibrated volumetric flasks were nearly filled with the appropriate buffer (two at each pH) at 50°C. Each flask was then spiked with 500 µL of the 500.49 µg/mL spiking solution (test substance in acetonitrile). The flasks were then made to the mark (50°C level) with the appropriate buffer, ultrasonicated for 5 minutes and then thoroughly shaken to give nominal concentrations of 2.5025 µg/mL.
Immediately, an aliquot (ca. 20 mL) of each buffered solution was poured into separate polystop bottles and cooled in a water bath at 20°C for ca 30 minutes prior to analysis (t = 0 hours). The flasks containing the remainder of each solution were stoppered, covered in aluminium foil to exclude light and placed in a water bath at 50°C.
After 2.4 hours and 5 days, further aliquots (ca 20 mL) of each buffered solution were taken and cooled as before, prior to analysis (t = 2.4 hours, 5 days).

TESTS 1 and 3 (at pH 5):

100 mL volumetric flasks were pre-calibrated at 50°C, 60°C and 70°C. The same procedure as the preliminary test was employed with just two flasks at each temperature (50°C, 60°C and 70°C) being spiked with 200 µL of ca 750 µg/mL of the spiking solution in acetone. Nominal concentrations of 1.4919 µg/mL (test 1) and 1.5292 µg/mL (test 3) were obtained. Aliquots were removed at t = 0 hours and various time points between 20 and 70% hydrolysis at 50°C for test 1 and three time points, two of which where greater than 30% hydrolysis had occurred (both at 60°C and 70°C) for test 3.

IDENTIFICATION OF HYDROLYSIS PRODUCTS:
The hydrolysis product of simazine was determined by retention time; a comparison was made between hydrolysed simazine and a client-supplied simazine derivative, simazine-2-hydroxy by HPLC.

Duration of test

Duration of test 1

Duration:

5 d

pH:

5

Temp.:

50 °C

Initial conc. measured:

2.502 µg/L

Remarks:

Preliminary test

Duration of test 2

Duration:

5 d

pH:

7

Temp.:

50 °C

Initial conc. measured:

2.502 µg/L

Remarks:

Preliminary test

Duration of test 3

Duration:

5 d

pH:

9

Temp.:

50 °C

Initial conc. measured:

2.502 µg/L

Remarks:

Preliminary test

Duration of test 4

Duration:

336 h

pH:

5

Temp.:

50 °C

Initial conc. measured:

1.492 µg/L

Remarks:

Test 1

Duration of test 5

Duration:

192 h

pH:

5

Temp.:

60 °C

Initial conc. measured:

1.529 µg/L

Remarks:

Test 3

Duration of test 6

Duration:

96 h

pH:

5

Temp.:

70 °C

Initial conc. measured:

1.529 µg/L

Remarks:

Test 3

Number of replicates:

2 replicates per pH and temperature

Positive controls:

no

Negative controls:

yes

Remarks:

Flasks containing buffer solutions only (one at each pH) were placed in the same water bath along with the test solutions for each of the three test procedures.

Results and discussion

Preliminary study:

After 5 days at 50°C, 16.4% hydrolysis occurred at pH 5 and no hydrolysis at pH 7 or 9. These results indicated that test 1 was required at pH 5 only.

Test performance:

A straight line plot was obtained for test 1 results, indicating pseudo first order behaviour. Therefore, test 3 was performed instead of test 2 (which is for non-pseudo first order behaviour).


In Test 3, the rate constants at 60°C and 70°C were calculated as 0.077889 and 0.16415 days-1, respectively, providing half-life times of 8.9 and 4.2 days.

Transformation products:

yes

Remarks:

Simazine-2-hydroxy

Identity of transformation products

No.:

#1

Reference

Reference substance name:

Unnamed

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

HYDROLYSIS:

According to the test method it can be estimated that 50% hydrolysis occurring in 2.4 hours at 50°C is equivalent to a half-life time of 1 day at 25°C and 10% hydrolysis occurring in 5 days at 50°C is equivalent to a half-life time of 1 year at 25°C.
Applying these criteria to the results obtained for simazine, the half-life at 25°C can be estimated to be greater than 1 year at pH 7 and 9. As no hydrolysis occurred after 5 days at 50°C, rate constants and half-lives could not be calculated at this temperature.
The half-life time at pH 5 was estimated to be 179 days at 25°C in test 3.

IDENTIFICATION OF HYDROLYSIS PRODUCTS:
Hydrolysis simazine and simazine-2-hydroxy both exhibited a slightly misshapen peak at 10.8 minutes which was not observed in the simazine solution. All the standards showed some minor peaks earlier in their chromatograms.

Dissipation DT50 of parent compound

Dissipation DT50 of parent compound 1

pH:

5

Temp.:

60 °C

Hydrolysis rate constant:

0.078 d-1

DT50:

8.9 d

Type:

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

Dissipation DT50 of parent compound 2

pH:

5

Temp.:

70 °C

Hydrolysis rate constant:

0.164 d-1

DT50:

4.2 d

Type:

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

Dissipation DT50 of parent compound 3

Key result

pH:

5

Temp.:

25 °C

Hydrolysis rate constant:

0.004 d-1

DT50:

179 d

Type:

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

Remarks on result:

other: Extrapolation to 25°C

Dissipation DT50 of parent compound 4

Key result

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Type:

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

Remarks on result:

other: Extrapolation to 25°C

Dissipation DT50 of parent compound 5

Key result

pH:

9

Temp.:

25 °C

DT50:

> 1 yr

Type:

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

Remarks on result:

other: Extrapolation to 25°C

Any other information on results incl. tables

Calibration data gave correlation coefficients ranging between 0.99559 and 0.99999, showing the detector response to be linear in the concentration ranges employed.

Some spuriously high recoveries were obtained in the preliminary test, but these were not considered to invalidate the study. Use of lower concentrations in tests 1 and 3 produced recoveries around 100% (90.6% - 106.7%).

No peaks at the characteristic retention volume of the test substance were obtained in the chromatograms of the blank solutions, indicating that the analytical procedure was free from interferences.

Table 1: Analytical data: Preliminary test

Time point (hours)	pH	% remaining (mean at each pH)	% hydrolysis (100 - % remaining)
0 hours	5	-	-
	7	-	-
	9	-	-
2.4 hours	5	94.919	5.1
	7	100.11	0
	9	96.198	3.8
5 days	5	83.574	16.4
	7	107.02	0
	9	104.65	0

 

Table 2: Analytical data: Test 1

Time point (hours)	pH	Mean % remaining
0	5	100
168	5	71.490
216	5	64.516
264	5	50.274
336	5	49.294

 

Table 3: Analytical data: Test 3

Time point (hours)	pH	Test temperature (°C)	Mean % remaining
0	5	60	110.00
24	5	60	90.494
96	5	60	71.020
144	5	60	63.372
192	5	60	52.308
0	5	70	99.930
72	5	70	59.579
96	5	70	52.341

Table 4: Identification of hydrolysis products

Solution	Retention times of peaks (minutes)
Simazine	6.6	7.6	8.6	-
Hydrolysed simazine	-	-	8.8	10.8
Simazine-2-hydroxy	-	-	8.2	10.8
Blank	-	-	-	-

Applicant's summary and conclusion

Validity criteria fulfilled:

not specified

Conclusions:

Simazine has been found to have a hydrolytic half-life time at 25°C of greater than 1 year at pH 7 and pH 9 and 179 days at pH 5. Simazine-2-hydroxy was identified as the hydrolysis product of simazine.