p-phenylenediamine

Phototransformation in water

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

Test material information

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 compound

Dissipation half-life of parent compound 1

DT50:

0.12 d

Test condition:

Overall photolysis half-life. These results demonstrate that the substance is readily degraded by sunlight.

Dissipation half-life of parent compound 2

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.