Ethyl [2-(4-phenoxyphenoxy)ethyl]carbamate

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

15 Sep 1993 to 18 Jan 1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical method:

high-performance liquid chromatography

other: Thin-Layer Chromatography (TLC)

Details on sampling:

- Sampling period: Irradiated samples were taken at the following time intervals: 0, 7, 14, 21, and 30 days. Non-irradiated samples were taken at 0, 14, and 30 days.
- Irradiated Volatile Sampling: Before analysis, the headspace from the irradiated sample vials was flushed through a volatile collection apparatus using a slight negative pressure. This was done on harvest day using the volatile trap series. Ethylene glycol (EG) traps contained 10 mL ethylene glycol (Fisher) while the potassium hydroxide (KOH) traps contained 15 mL of 10% KOH (100 g Fisher KOH diluted to 1 L water). Volatile traps were attached to the vacuum Y-joint using an 18 1/2 gauge needle which was pierced through the septum of empty Trap #3. The desired bubbling speed (between barely bubbling and one that allowed the foamy trap solution to start up the outlet teflon tubing) for each trap series was regulated with pinch clamps placed on the silicone tubing which connected the traps to the Y-joint. Next, the sample vial was attached to the trap series using the stainless steel tubing. If any fine adjustment to the bubbling rate was required, the pinch clamp was then used. The sample vials were purged for 10 to 15 minutes. The sample vial and trap series were disconnected by loosening the cap on the sample vial, loosening the cap on Trap #2, and finally disconnecting empty Trap #3 from the vacuum Y-joint.
- Storage of Samples and Standards: All harvested samples were stored in a mechanical convection incubator (GCA Model 4EM) at 27 – 30 ˚C. The quantitation results of the non-irradiated samples show the hydrolytic stability of the test substance under these conditions. All standard solutions and isolated degradates (foil wrapped) were stored in a refrigerator at 5° to 8°C. All solid standards were stored in a freezer at -16° to -23°C.

Buffers:

The pH 7 buffer was prepared using two solutions. The first solution was prepared by dissolving 4.6 g of sodium phosphate, monobasic (monohydrate), in 500 mL of deionized water, making a 0.067 molar (M) solution. Another solution was prepared by dissolving 5.8 g of potassium phosphate, dibasic, in 500 mL of deionized water (0.067M). The test buffer was prepared by adding 30 mL of the 0.067M sodium phosphate solution to 61 mL of the 0.067M potassium solution and diluting to 1000 mL with deionized water. This buffer solution was then adjusted to pH 7.0 with a few drops of the sodium phosphate solution (0.067M). The buffer was sterilized by filtering through a 0.2 µ membrane filter using SOP 6.23. The water used was processed through the recirculating Hydro Picotech system. The water exceeded all ASTM Type 1 standards and had the following characteristics:
- pH: 5.5
- Resistivity: 18 megohm—cm
- TOC: < 5 ppb

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 290

Details on light source:

Equipment: The artificial sunlight exposure was accomplished using a Heraeus Suntest Accelerated Exposure Unit and programmable timer.
- Filter: The xenon arc light source equipped with pre-aged borosilicate UV glass filters which absorbs wavelengths below 290 nm.
- Intensity: The intensity of the xenon arc lamp was monitored using an International Light unit, model 1700, throughout the study to insure the samples were irradiated at intensities comparable to natural sunlight. The average intensity of natural sunlight measured on July 11, 1991 (nine readings from 9:00 A.M. to 5:00 was 410 W/m2. The intensity of the artificial light was set at 1.14E-02 W/m2 with the international Light Unit which correlates to 410 W/m2 on the Radialux unit. This intensity was measured at the start and end of the study.
- Spectral distribution: The distribution, 200-700 nm, of the xenon arc lamp is compared to the distribution of natural sunlight.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test apparatus/vessels: 4.9 mL (1 dram) silylated borosilicate vials
- Sterilisation method: All glassware was sterilized by autoclaving before use.
- Details of traps for volatile: Volatiles were trapped by 2 KOH and 2 ethylene glycol traps

TEST MEDIUM
- Volume used/treatment: 3 mL

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

- Irradiated Incubations: The dosed vials were inverted and placed in the sample rack. The water level of the waterbath did not completely submerge the inverted vial. The samples were irradiated on alternating 12 hour light and dark cycles with artificial sunlight at 1.14E-2 w/cm2 is equivalent to 410 W/m2 . This is comparable to the natural sunlight average intensity of 410 W/m2 found on July 11, 1991.

- Non-irradiated Incubation: Non-irradiated samples were wrapped in aluminum foil and placed in the constant temperature chamber. The samples were incubated in the constant temperature chamber under dark conditions at 25 ± 1°C.

- Temperature monitoring: The irradiated sample temperature was monitored by inserting a thermocouple into a surrogate vial containing the same amount of buffer as the sample vials. The analog output from the thermocouple was recorded using the environmental monitoring system. The temperature of the non-irradiated samples in the constant temperature chamber was recorded on the unit's hydrothermograph.

Duration:

30 d

Temp.:

25 °C

Initial conc. measured:

1.3 mg/L

Reference substance:

not specified

Dark controls:

yes

Parameter:

not specified

% Degr.:

57.3

Sampling time:

30 d

Test condition:

irradiated

Remarks on result:

other: HPLC result

% Degr.:

6.9

Sampling time:

30 d

Test condition:

non-irradiated

Remarks on result:

other: HPLC result

% Degr.:

62.8

Sampling time:

30 d

Test condition:

irradiated

Remarks on result:

other: TLC result

% Degr.:

2.4

Sampling time:

30 d

Test condition:

Non-irradiated

Remarks on result:

other: TLC result

Key result

DT50:

23.1 d

Test condition:

irradiated

Transformation products:

not specified

Remarks:

M2, M10, M16, M18

Details on results:

- Mass balance: The material balance for the irradiated samples ranged from 92.4% to 100.0%. These numbers were obtained by comparing the radioassayed concentration to the original applied concentration. The ethylene glycol traps contained very low levels of radioactivity for all time points. values ranged from < 0.03% to 0.23% for individual replicates at all time intervals. Potassium hydroxide traps (KOH) also contained minimal radioactivity, ranging from < 0.048% to 6.0 %.The material balance for the non-irradiated samples was excellent, ranging from 98.7% to 100.0% of the 14C applied.

- Characterization of Samples: The irradiated and nonirradiated samples were characterized by HPLC and 2D-TLC.Selected non-radioactive standards were co-injected by HPLC and co-applied by 2D-TLC. A total of 9 HPLC peaks were seen in the irradiated samples with only one (peak 2) comprising over 10% of the applied dose except for Peak 1. Peak 1 co-chromatographed with unchanged parent substance, while peak 2 co-chromatographed with M16 by HPLC. Peak 2 also co-chromatographed with standard M18, but characterization by 2D-TLC showed minimal amounts of M18 present in the samples. Peaks 3 and 4 eluted where standards M2 and M10 eluted, respectively. Peaks 5-9 did not match any of the standards available. The non-irradiated HPLC characterization showed only one predominant peak (peak 1) which co-chromatographed with the parent substance.
The 2D-TLC profiles of the irradiated samples gave similar results as showing several localized zones. Zone 1 co-chromatographed with the parent substance while Zone 4 co-chromatographed with and M2. In addition, 14 other minor zones were seen below 10% of the applied dose. Zones 3 and 8 co-chromatographed with standards M10 and M18, respectively. Zone 2 was at the origin while zones 5 - 7 and 9-16 did not co-chromatograph with any standards. In the 2D-TLC characterization of the non-irradiated samples, the major zone, zone 1, co-chromatographed with the test substance.

- Quantitation: Reverse phase HPLC quantitation of the irradiated samples produced the same peaks as seen during characterization. Peak 2 (M16 with minimal M18) rose to 10.4% on day 14 and slightly increased to 16.9% by day 30. Peak 1 (unchanged parent) decreased from 96.9% on day 0 to 70.8% on day 14 and then further decreased to 42.7% by day 30. Peaks 3 and 4 (M2 and M10) averaged 6.9% and 7.1% by day 30. Peaks 5-9 each were all and thus were not further pursued due to these low levels. "other radioactivity" (Others) was the summation of all the radioactivity eluting throughout the chromatographic run that was not contained in the previously mentioned peaks. This radioactivity was composed of minor multicomponent regions and did not contain any discernible peaks. The single maximum 14C level in any one quantitation vial ranged from 0.1% - 0.8% of the applied dose.
No detectable degradation was seen with parent at 96.9% of the applied radioactivity at day 0 and 93.1% on day 30. The summation of other radioactivity seen of minor multicomponent regions ranged from 0.9% to 7.1% of the applied dose with no more than 0.3% in any single vial. 2D-TLC quantitation of the irradiated samples confirmed the HPLC results of parent. Zone 1 (the test substance) decreased from 99.6% at day 0 to 37.2% by day 30. Zones 2 (origin) and 3 (M10) never averaged more than and 3.9%, respectively. Zone 4 (M16 plus minimal M2) increased to 11.1% by day 14 and then slightly increased to 13.2% and 20.8% by days 21 and 30, respectively. Zones 5-7 never averaged more than 3.6% of the radioactivity while zone 8 increased to by day 14. Zone 8 (M18) then declined to 1.6% an average of 1.0% by day 30. Zones 9-16 never exceeded an average of more than 4.7% at any time interval. The summation of other radioactive regions ranged between 0.4% and 8.7% with no single quantitation vial containing more than 2.8%.
To confirm the non-irradiated HPLC quantitation, the nonirradiated samples were also quantitated by 2D-TLC. Results were similar showing 99.6% on day 0 and no detectable degradation through day 30 (97.6%). Other radioactive regions contained no more than 1.0% in any single vial.

- Mass spectral Analyses: Isolated peak 2 was partitioned and the chloroform fraction derivatized and analysed by GC/MS using electron impact ionization. The retention time (~12.8 minutes) and spectra matched the derivatized M16 standard. The extracted ion chromatogram showed peaks for both sample and standard with m/z 340 corresponding to M+115. other fragments seen in both spectra were 75, 129, and 207. This analysis confirmed that peak 2 was M16. Isolated peak 1 was also analysed by GC\MS using EI. The retention time (~17.4 minutes) and spectra matched the test substance standard. Fragments 256, 186, 116 and 88 were seen in both spectra, confirming that peak 1 was parent substance. Also seen was the molecular ion, m/z = 301.

- Half-results: Degradation of irradiated test substance demonstrated pseudo--first order kinetics. HPLC quantitation of the irradiated samples indicated the test substance had a half-life of 23.1 days with a rate constant of -0.03/days. Correlation of the half-life data points fit excellently to the line at -0.979. The rate constant was obtained from the slope of the line. There was no degradation seen of the test substance under nonirradiated conditions in aqueous solution with 96.9% parent on day 0 and 93.1% on day 30.

Table 1. Mass balance

a) irradiated samples

Sample day	KOH -1	KOH -2	Total KOH	EG-1	EG-2	Total EG	Aqueous samples	Total balance
Day 0A	N/A	N/A	N/A	N/A	N/A	N/A	100	100
Day 0A	N/A	N/A	N/A	N/A	N/A	N/A	100	100
Day 4A	<0.048	<0.048	<0.048	<0.033	<0.033	<0.033	92.35	92.35
Day 4B	<0.048	<0.048	<0.048	<0.033	<0.033	<0.033	95.86	95.86
Day 7A	0.6	0.33	0.93	<0.033	<0.033	<0.033	98.38	99.31
Day 7B	0.53	<0.048	0.53	<0.033	<0.033	<0.033	94.34	94.87
Day 14A	1.76	0.74	2.5	0.23	<0.033	0.23	95.69	95.69
Day 14B	1.87	0.59	2.46	<0.033	<0.033	<0.033	97.07	99.53
Day 21A	1.15	<0.048	1.15	<0.033	<0.033	<0.033	95.44	96.59
Day 21B	0.87	<0.048	0.87	<0.033	<0.033	<0.034	97.46	98.33
Day 30A	5.55	0.47	6.02	0.17	<0.033	0.17	93.52	99.71
Day 30B	3.6	1.02	4.62	0.23	<0.033	0.23	91.83	96.68

Day 0 : Balance were normalized to 100%

 

b) Unirradiated samples

Sample Day	Balance
Day 0 A	*100.0
Day 0 B	*100.0
Day 14 A	*100.0
Day 14B	*100.0
Day 30 A	*100.0
Day 30 B	98.7

* Balance greater than 100% and less than were reported as 100%.

Table 2. HPLC quantitation of the samples

a) irradiated samples 

Time interval	replicate	% recovery	test substance	M16 and M18	M2	M10	Unknown 1	Unknown 2	Unknown 3	Unknown 4	Unknown 5	Others total
Day 0	A	96.9	96.1	nd	nd	nd	nd	nd	nd	nd	nd	3.9
Day 0	B	92.9	97.7	nd	nd	nd	nd	nd	nd	nd	nd	2.3
Day 0	average		96.9	nd	nd	nd	nd	nd	nd	nd	nd
Day 4	A	92.8	84.3	3	nd	nd	nd	nd	nd	nd	nd	5.1
Day 4	B	94.5	86.5	3.4	nd	nd	nd	nd	nd	nd	nd	6
Day 4	average		85.4	3.2	nd	nd	nd	nd	nd	nd	nd
Day 7	A	92.5	84.2	5.6	1.7	1.3	nd	nd	nd	nd	nd	5.7
Day 7	B	93	78.6	5.7	1.5	1.3	nd	nd	nd	nd	nd	7.2
Day 7	average		81.4	5.7	1.6	1.3	nd	nd	nd	nd	nd
Day 14	A	97.6	69.6	9	1.8	1	2.4	2.4	1.3	3.3	nd	2.4
Day 14	B	91.1	71.9	11.7	2.8	2.3	0	0.2	0.6	0.2	1.2	5.9
Day 14	average		70.8	11.4	2.3	1.7	1.2	1.3	1	1.9	0.6
Day 21	A	89.4	61.2	13.9	2.3	0.9	2.8	5	1.4	4.7	0	3.1
Day 21	B	90	66.1	12.8	2.2	1	3	3.1	2.3	4.4	0	2.5
Day 21	average		63.7	13.4	2.3	1	2.9	1.1	1.9	1.6	0
Day 30	A	90.2	42.3	17.7	7.2	7.1	6.9	0	0.8	2.2	3.2	6.1
Day 30	B	90.6	43	16	6.5	7.1	6.4	0	1.5	1.5	3.1	6.8
Day 30	average		42.7	16.9	6.9	7.1	6.7	0	1.2	1.9	3.2

“Others" are minor multicomponent regions eluting throughout the chromatographic runs. “Others” is calculated as the sum of radioactivity not included in the defined peaks.

b) unirradiated samples

Time interval	Replicate	% recovery	Parent	Others
Day 0	A	96.9	96.1	3.9
Day 0	B	92.9	97.7	2.3
Day 0	average		96.9
Day 14	A	98.5	99.1	0.9
Day 14	B	102.2	97.4	2.6
Day 14	average		98.3
Day 30	A	104.0	94.5	5.4
Day 30	B	103.7	91.6	7.1
Day 30	average		93.1

“Others" are minor multicomponent regions eluting throughout the chromatographic runs. “Others” is calculated as the sum of radioactivity not included in the defined peaks.

Table 3. TLC quantitation of the samples

a) irradiated samples

Time interval	replicate	% recovery	test substance	origin	M10	M2 and M16	Unknown 1	Unknown 2	Unknown 3	M18	Unknown 4	Unknown 5	Unknown 6	Unknown 7	Unknown 8	Unknown 9	Unknown 10	Unknown 11	others
Day 0	A	100.5	99.6	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	0.4
Day 0	B	98.6	99.5	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	0.5
Day 0	average		99.6	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd
Day 4	A	92.8	87.5	nd	0.9	3.5	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	0.5
Day 4	B	94.6	87.7	nd	1.2	4.9	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	2.1
Day 4	average		87.6	nd	1.1	4.2	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd	nd
Day 7	A	104.6	80.6	nd	1.7	8.7	0.8	1.5	1.4	0.4	nd	0.5	nd	nd	nd	nd	nd	nd	2.9
Day 7	B	102.6	80.3	nd	1.2	6.7	0.9	1.0	0.7	0.5	0.9	nd	nd	nd	nd	nd	nd	nd	2.0
Day 7	average		80.5	nd	1.6	7.7	0.9	1.3	1.1	0.5	0.5	0.3	nd	nd	nd	nd	nd	nd
Day 14	A	91.6	68.1	0.4	0.7	11.3	1.4	0.6	0.4	1.3	7.9	nd	With unknown 4	With unknown 4	nd	nd	nd	nd	0.8
Day 14	B	92.3	69.7	0.6	2.7	10.8	1.2	3.0	1.4	1.9	1.4	0.5	1.0	2.4	nd	nd	nd	nd	0.6
Day 14	average		68.9	0.5	1.7	11.1	1.3	1.8	0.9	1.6	4.7	0.3	0.5	1.2	nd	nd	nd	nd
Day 21	A	92.7	63.0	1.2	2.1	14.8	nd	2.0	0.5	1.5	1.9	nd	1.6	1.4	nd	1.3	1.4	1.0	1.7
Day 21	B	101.5	68.0	nd	1.7	11.5	nd	2.3	0.8	0.7	1.2	0.7	1.4	1.7	0.5	nd	nd	nd	7.0
Day 21	average		65.5	0.6	1.9	13.2	nd	2.2	0.7	1.1	1.6	0.4	1.5	1.6	0.3	0.7	0.7	0.5
Day 30	A	102.7	37.0	0.8	3.9	19.6	nd	3.1	2.1	1.6	3.8	1.9	1.9	2.1	1.2	2.7	2.4	0.7	8.7
Day 30	B	98.0	37.3	0.5	3.9	22.0	nd	4.0	1.9	0.4	2.8	1.4	2.0	1.9	0.9	2.2	2.1	0.8	7.9
Day 30	average		37.2	0.7	3.9	20.8	nd	3.6	2.0	1.0	3.3	1.7	2.0	2.0	1.1	2.5	2.3	0.8

“Others" are minor multicomponent regions eluting throughout the chromatographic runs. “Others” is calculated as the sum of radioactivity not included in the defined peaks.

 

b) unirradiated samples

Time interval	Replicate	% recovery	Parent	Others
Day 0	A	100.5	99.6	0.4
Day 0	B	98.6	99.5	0.5
Day 0	average		99.6
Day 14	A	102.2	99.3	0.7
Day 14	B	102.1	99.6	0.4
Day 14	average		99.5
Day 30	A	105.5	98.1	1.9
Day 30	B	109.7	97.1	1.6
Day 30	average		97.6

“Others" are minor multicomponent regions eluting throughout the chromatographic runs. “Others” is calculated as the sum of radioactivity not included in the defined peaks.

  

Table 4. calculated half-life and rate constant

Time interval	Average % dose parent	Ln average % of dose
Day 0	96.90	4.574
Day 4	85.40	4.447
Day 7	81.40	4.399
Day 14	70.80	4.260
Day 21	63.70	4.154
Day 30	42.70	3.754

* Day 0 samples are common for both irradiated and non-irradiated conditions

Calculated half life = 23.1 days.

Validity criteria fulfilled:

yes

Conclusions:

In a photodegradation study performed in accordance with EPA 161-2, the photolytic half-life for the test substance was calculated to be 23.1 days.

Executive summary:

The direct photodegradation of the test substance was determined in a study that was performed according to EPA guideline 161-2, in compliance with GLP criteria. In this study, [β-phenyl-ring]-labelled test substance was added to buffered aqueous solutions at pH 7. All solutions were irradiated in 12 hour dark-light cycles by a Xenon light source (including UV-filter with cut-off at 290 nm) for up to 30 days at 25 ± 1°C. Dark controls were included. Light intensity was measured at the beginning and end of the study and was 410 W/m2. Duplicate samples were taken after 0, 4 (irradiated), 7 (irradiated), 14, 21 (irradiated) and 30 days.

The test substance is stable in dark solutions (HPLC method showed 93.1% on day 30 and TLC method showed 97.6%). In irradiated solutions, the test substance degraded to 42.7% AR at 30 days (analysis by HPLC). Several photodegradates were detected, of which one exceeded 10% AR (M16; max 16.9% AR at 30 days). This was identified and confirmed by HPLC, TLC and GC-MS. All other photoproducts were < 10% AR. The TLC quantitation showed that in irradiated solutions, test substance degraded to 37.2% AR at 30 days, similar to the HPLC quantitation. Several photodegradates were detected as well. Only M16 plus minimal M2 exceeded 10% AR (max 20.8% AR at 30 days). In an EPA 161-2 guidance followed study, the photolytic half-life for the test substance was calculated to be 23.1 days.

Description of key information

All available data was assessed and the studies representing the worst-case effects were included as key study. Other studies are included as supporting information. The key studies are considered to be worst-case and were selected for the CSA.

DT50 = 23.1 days irradiation with 12 hour dark-light cycles by Xenon arc lamp (410 W.m-2; >= 290 nm) for 30 days , 25 °C, EPA 161 -2 Clark 1995

Key value for chemical safety assessment

Half-life in water:

23.1 d

Additional information

The direct photodegradation of the test substance was determined in a study according to EPA guideline 161-2, and was in compliance with GLP criteria. In this study, [β-phenyl-ring]-labelled test substance was added to buffered aqueous solutions at pH 7. All solutions were irradiated in 12 hour dark-light cycles by a Xenon light source (including UV-filter with cut-off at 290 nm) for up to 30 days at 25 ± 1°C. Dark controls were included. Light intensity was measured at the beginning and end of the study and was 410 W/m2. Duplicate samples were taken after 0, 4 (irradiated), 7 (irradiated), 14, 21 (irradiated) and 30 days.

The test substance is stable in dark solutions (HPLC method showed 93.1% on day 30 and TLC method showed 97.6%). In irradiated solutions, the test substance degraded to 42.7% AR at 30 days (analysis by HPLC). Several photodegradates were detected, of which one exceeded 10% AR (M16; max 16.9% AR at 30 days). This was identified and confirmed by HPLC, TLC and GC-MS. All other photoproducts were < 10% AR. The TLC quantitation showed that in irradiated solutions, test substance degraded to 37.2% AR at 30 days, similar to the HPLC quantitation. Several photodegradates were detected as well. Only M16 plus minimal M2 exceeded 10% AR (max 20.8% AR at 30 days). In an EPA 161-2 guidance followed study, the photolytic half-life for the test substance was calculated to be 23.1 days.