Registration Dossier

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:
guideline study with acceptable restrictions
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:
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 of the synthetic humic water. These guideline differences and potential impacts were not discussed. The study was run using two concentrations, 5 µM and 10 µM.
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
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/June & July
Other: Skies were clear during the whole exposure
Sensitiser (for indirect photolysis)open allclose all
Type of sensitiser:
other: humic acid
Details on sensitiser:
synthetic humic water, pH 7
Concentration of sensitiser:
other: Absorbance (1cm cell @ 290 nm) = 0.05 for 10 µM test substance studies
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 for 5 µM test substance studies
Dark controls:
yes
Remarks:
No significant losses were observed with the dark controls.

Results and discussion

Preliminary study:
Indirect photolysis was negligible, and the presence of humic acid had little effect on the photolysis rate under the test conditions. A definitive study was conducted to ensure that the data requirements were fulfilled and to obtain accurate measurement of the direct photolysis rate constant.
Quantum yield (for direct photolysis):
0.05
Rate constant (for indirect photolysis):
1.7 other: d-1
Dissipation half-life of parent compound
DT50:
0.26 d
Test condition:
Overall photolysis half-life
Transformation products:
not measured

Any other information on results incl. tables

For the initial screening study, the rate of aqueous photolysis for the test substance was approximately 6.0 d-1 in both distilled water and humic acid. The test guidelines specify that a definitive study is not required in cases where the ratio of the indirect to direct rate constants is less than 2. However, a definitive study was conducted to obtain an accurate measurement of the photolysis rate constant. Under these experimental conditions, the photolysis did not follow first order kinetics.

An additional study was conducted with a lower test substance concentration to minimize any photocatalytic effect (which may account for the deviation from first order kinetics) and twice the humic acid concentration to enhance any sensitizing effect. Under these conditions, humic acid had a sensitizing effect on the rate of photolysis, and the photolysis followed first order kinetics.

Applicant's summary and conclusion

Conclusions:
This study concluded that the test substance is very photolabile and both direct and indirect photolysis contribute to its phototransformation.
Executive summary:

Tests were conducted to determine whether natural humic acid significantly enhances the aqueous photolysis of the test substance. Quartz tubes containing the test substance in either distilled water or synthetic humic water at pH 7 were exposed to summer sunlight. Four studies were run using two different test substance concentrations; initial two studies were at 10 µM and the two additional studies were at 5 µM. The concentration of the test substance was monitored at various times and analysed using high performance liquid chromatography (HPLC). The exposure time varied from 30 minutes to 3 hours 45 minutes.

 

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: 1.0 d-1

           Indirect photolysis rate constant: 1.7 d-1

           Overall photolysis rate constant: 2.7 d-1

           Overall photolysis half-life: 0.26 d

 

The test substance is very photolabile, and both direct and indirect photolysis contribute to its phototransformation. The direct photolysis rate constant is dependent on the concentration of the test substance; the value of 1.0 d-1 applies to concentrations below 0.5 ppm (5 µM). Indirect photolysis is the major pathway at low concentrations but direct photolysis becomes predominant at higher concentrations as a result of photocatalysis by products.