Simazine

Phototransformation in water

Administrative data

Endpoint:

phototransformation in water

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:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1995

Report date:

1995

Materials and methods

Study type:

direct photolysis

Test guideline

Qualifier:

no guideline followed

Principles of method if other than guideline:

Aqueous solutions of simazine and an actinometer were subjected to artificial light from a xenon arc lamp while under constant temperature at 25°C. Solutions of simazine and actinometer were also maintained in the dark to act as controls. At six time points subsamples were removed from the test solutions and analysed to monitor any decrease in test substance concentration.

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

Study design

Radiolabelling:

no

Analytical method:

high-performance liquid chromatography

Details on sampling:

PRELIMINARY TEST:
The solutions within the Suntest box were analysed at Day 0 (start of test) and again at Day 3. At Day 3, the simazine dark control was also analysed.

EXTENDED TEST:
On Days 0, 3, 6, 7, 9, 10 aliquots of ~3 mL were removed from each cell in the Suntest box for analysis. At each time point the actinometer solution stored in the dark at ambient temperature was also analysed. The simazine dark control solution was analysed on Days 3, 7 and 10.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290 - <= 500

Details on light source:

The irradiance of the xenon arc lamp was measured in situ in the Suntest chamber. The cosine diffuser of the radiometer was placed in the appropriate positions underneath the quartz lids used to cover the sample cells. The spectrometer slit width was 1.25 mm. Measurement of the irradiance was taken at 5 nm intervals in the range 290 - 500 nm.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: Suntest cells: Borosilicate glass, double jacketed with quartz lids

TEST MEDIUM
- Kind and purity of water: Distilled water
- Preparation of test medium: A test solution of simazine in distilled water was prepared at half saturation concentration.

REPLICATION
- No. of replicates (dark): 2
- No. of replicates (irradiated): 2

ACTINOMETER:
Paranitroacetophenone (PNAP) in acetonitrile was used as the actinometer system.

PRELIMINARY TEST:
Two cells were placed in the Suntest apparatus to be subjected to the maximum level irradiance in the ultraviolet visible range from a xenon arc lamp. Test solution was poured into one cell and actinometer solution in the other. Quartz lids were placed over each cell.
The Suntest box was switched on and the cells irradiated. The solutions within the Suntest box were analysed at Day 0 (start of test) and again at Day 3. At Day 3, the simazine dark control was also analysed. From this information the percentage drop over 3 days was calculated and an estimation of the timing of the 6 data points for the extended test was made.

EXTENDED TEST:
The test cells were set up in an identical manner to the preliminary test. The third cell was filled with simazine solution and placed outside the Suntest box and covered with aluminium foil to exclude light (simazine dark control).
The Suntest box was switched on and the cells irradiated. At six time points (Days 0, 3, 6, 7, 9, 10) aliquots of ~3 mL were removed from each cell in the Suntest box for analysis. At each time point the actinometer solution stored in the dark at ambient temperature was also analysed. The simazine dark control solution was analysed on Days 3, 7 and 10.

Duration of test at given test condition

Duration:

10 d

Temp.:

25 °C

Initial conc. measured:

2.335 other: µg/mL

Reference substance:

no

Dark controls:

yes

Remarks:

Filled with simazine solution and placed outside the Suntest box and covered with aluminium foil

Results and discussion

Preliminary study:

The preliminary test showed a drop of 35% in simazine concentration over 3 days.

Test performance:

Simazine dark control data showed that all the results lie in the range 92.5 - 97.5% recovery showing the solution to be stable in the dark.
Actinometer dark control data show that all the results lie in the range 96.2 - 98.8% recovery showing the solution to be stable in the dark.
No peaks were seen at the characteristic retention time for the blank solutions in either of the methods showing them to be free from interferences.

Quantum yield (for direct photolysis):

0

Dissipation half-life of parent compound

Key result

DT50:

7.2 d

Test condition:

Suntest apparatus

Predicted environmental photolytic half-life:

36 days

Transformation products:

not measured

Details on results:

The rate constants for simazine and the actinometer were 0.095868 days-1 and 0.068883 days-1, respectively.

The half-life of simazine in the Suntest apparatus was calculated as 7.2 days.

The half-life of simazine in the environment for surface waters at latitude 40 - 50°N was calculated as 36 days.

The half-life of 36 days is valid only for direct transformation, in mid-day sunlight conditions in the top mm of a neutral aquatic system of latitude 40 - 50°N. It can, however, be used as a rough estimate of the persistence of simazine.

Any other information on results incl. tables

Photolysis calibration data showed that the analytical methods were linear over the standard concentration ranges used.

Simazine quality control data showed that all the results lie in the range 96.0 - 100.5% recovery.

Applicant's summary and conclusion

Validity criteria fulfilled:

not applicable

Conclusions:

Simazine has been found to photodegrade in the Suntest apparatus with a half-life time of 7.2 days. The quantum yield for direct photodegradation was established as 1.25E-05. Using published tables of irradiance values, an environmental half-life time for simazine of 36 days was obtained for surface waters at latitude 40 - 50 °N.