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Administrative data

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
This GLP study generally follows the guideline. There are several deviations in the preparation and aging of the synthetic humic water, including no information on the measurement of DOC and the pre-aging time was seven days not three. These guideline differences and potential impacts were not discussed.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1990
Report date:
1990

Materials and methods

Study type:
indirect photolysis
Test guideline
Qualifier:
according to guideline
Guideline:
EPA OTS 795.70 (Indirect Photolysis Screening Test: Sunlight Photolysis in Waters Containing Dissolved Humic Substances)
Deviations:
yes
Remarks:
The study generally follows the guideline. There are several deviations in the preparation synthetic humic water. These guideline differences and potential impacts were not discussed.
GLP compliance:
yes

Test material

Constituent 1
Details on test material:
- Purity: 99.72%

Study design

Radiolabelling:
not specified
Analytical method:
high-performance liquid chromatography
Light source:
sunlight
Details on light source:
Location: roof, 38ºN, facing south and angled at ~30º to the horizon
Time of year/month: summer/August
Other: Skies were clear during the whole exposure
Sensitiser (for indirect photolysis)
Type of sensitiser:
other: humic acid
Details on sensitiser:
synthetic humic water, pH 7
Concentration of sensitiser:
other: Absorbance (1cm cell @ 290 nm) = 0.1
Dark controls:
yes
Remarks:
(No significant losses were observed with the dark controls.)

Results and discussion

Preliminary study:
Loss of the test substance was 1.6 times faster in synthetic humic water (SHW) than distilled water and the half life in SHW was less than an hour. Therefore, according to the guideline, a definitive study was not necessary.
Quantum yield (for direct photolysis):
0.02
Rate constant (for indirect photolysis):
2.2 other: d-1
Dissipation half-life of parent compoundopen allclose all
DT50:
0.12 d
Test condition:
Overall photolysis half-life. These results demonstrate that the substance is readily degraded by sunlight.
DT50:
0.32 d
Test condition:
Indirect photolysis half-life
Transformation products:
not measured

Any other information on results incl. tables

Distilled Water (DW) and Synthetic Humic Water (SHW) Screening Study Results

Water Type

Light Conditions

Sample

Time (PDT)

Peak Height (mm), Injection #1

Peak Height (mm), Injection #2

Average Height, C (mm)

ln(C0/Ct)

Test Substance (µM)

Test Substance % Reacted

DW

Start (Time 0)

A

11:20

43.2

43.9

44

0

10.5

0

DW

Start (Time 0)

B

11:20

44.8

44.2

DW

Dark

A

12:00

44.4

45.2

45.3

-0.029

10.8

-3

DW

Dark

B

12:00

45.3

46.1

DW

Light

A

12:00

22.2

22.2

22

0.693

5.2

50

DW

Light

B

12:00

22.1

21.3

SHW

Start (Time 0)

A

11:20

42.8

43

42.3

0

10.1

0

SHW

Start (Time 0)

B

11:20

41.9

41.6

SHW

Dark

A

12:00

44.2

43.6

44

-0.039

10.5

-4

SHW

Dark

B

12:00

44.5

43.5

SHW

Light

A

12:00

15.2

14.7

14.2

1.092

3.4

66

SHW

Light

B

12:00

14.2

12.8

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
The calculated overall half-life (in synthetic humic water) is less than 1 hour, the test substance is considered “photolabile” and the definitive study is not applicable.
Executive summary:
Tests were conducted to determine whether natural humic acid significantly enhances the aqueous photolysis of the test substance. During the preliminary screening test, quartz tubes containing the test substance in distilled water and synthetic humic water at pH 7 were exposed to summer sunlight. The concentration of the test substance was monitored at time zero and 40 minutes using high performance liquid chromatography (HPLC). No significant losses were observed in the dark controls, and the loss of the test substance in sunlight was 1.6 times faster in synthetic humic water than in distilled water. Because the calculated overall half-life (in synthetic humic water) is less than 1 hour, the test substance is considered “photolabile” and the definitive study is not applicable.   The results yielded the following kinetic data corresponding to photolysis at 40°C in summer at the surface of a flat water body with an absorbance of 0.1 at 290 nm: - Direct photolysis rate constant: 3.7 d-1 - Indirect photolysis rate constant: 2.2 d-1 - Overall photolysis rate constant: 5.9 d-1 - Overall photolysis half-life: 0.12 d (56 min) The test substance is very photolabile, and both direct and indirect photolysis contribute significantly to its phototransformation.

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