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Environmental fate & pathways

Phototransformation in water

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Administrative data

Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2016
Report Date:
2016

Materials and methods

Study type:
indirect photolysis
Test guidelineopen allclose all
Qualifier:
according to
Guideline:
EPA OPPTS 835.5270 (Indirect Photolysis Screening Test: Sunlight Photolysis in Waters Containing Dissolved Humic Substances)
Deviations:
no
Qualifier:
according to
Guideline:
other: OECD Guideline for Testing of Chemicals Proposal for a New Guideline Photo transformation of Chemicals in Water - Direct and Indirect Photolysis
Deviations:
no
GLP compliance:
yes

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
liquid
Details on test material:
- Purity: not reported as such

Study design

Radiolabelling:
not specified
Analytical method:
gas chromatography
liquid chromatography
mass spectrometry
Details on sampling:
Sampling intervals: Two test vessels with each type of the media were analyzed on Day 0. Two light exposed and two dark control test vessels were removed from SUNTEST CPS+ chamber and incubator, respectively, at each sampling interval (after the periods corresponding to approximately 4, 8, 12, and 19 days of xenon lamp irradiation) and submitted for analyses. Light exposed samples were picked from the SUNTEST CPS+ chamber.
Buffers:
- pH: 7.0
- Type and final molarity of buffer: 0.01 M
The first batch of 0.01 M pH 7.0 phosphate buffer was prepared by weighing 1.3748 g of KH2PO4 and 1.7069 g of K2HPO4 into a 2-L, volumetric flask and bringing it to the volume with HPLC-grade water. The pH of the resultant solution was adjusted to 7.0 using 2N HCI. The prepared buffer solution was placed in glass bottles sterilized by autoclaving at approximately 121°C and 15 psi for 30 min for the preparation of SHW with absorbance of 0.50.

The second batch of 0.01 M pH 7.0 phosphate buffer was prepared by weighing 0.6801 g of KH2PO4 and 0.8537 g of K2HPO4 into a 1-L, volumetric flask and bringing it to the volume with HPLC-grade water. The pH of the resultant solution was determined as pH 7.0. The prepared buffer solution was placed in glass bottles, sterilized by autoclaving at approximately 121°C and 15 psi for 30 min, and was used for the preparation of SHW solution with absorbance of 0.05 Absorbance Units and test solution preparation.
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
ca. 200 - ca. 800
Relative light intensity:
ca. 300 - ca. 400
Details on test conditions:
Refer Table 1 in any other information on materials and methods incl. tables
Duration of test at given test condition
Duration:
18.5 d
Temp.:
25 °C
Initial conc. measured:
2.978 mg/L
Reference substance:
yes
Remarks:
6:2 FTOH, 1H-PFHx, 6:2 FTO, PFHxA, PFHpA, 6:2 FTCA and 6:2 FTUCA
Dark controls:
yes

Results and discussion

Dissipation half-life of parent compoundopen allclose all
Key result
DT50:
721 d
Test condition:
Solar irradiation at horizontal surface in pH 7.0 buffer
Key result
DT50:
875 d
Test condition:
Solar irradiation at horizontal surface in synthetic natural water
Predicted environmental photolytic half-life:
Phototransformation rate corresponds to a half-life of 875 days in natural water bodies or 721 days in pH 7.0 aqueous buffer.
Details on results:
Temperature Conditions:
The water temperature in SUNTEST CPS+ chamber water bath ranged from 23.0°C to 26.9°C with an overall mean and standard derivation of 24.7 ± 1.1°C during the entire Phase II study. The temperature of the incubator for dark control samples ranged from 23.9°C to 26.8°C with an overall mean and standard deviation of 25.3±0.7°C.
Once during the study, due to the power shutdown in the facility, the thermometers in the water bath and incubator recorded minimal temperatures 12.5 °C and -5.0 °C, respectively and the light in the SUNTEST CPS+ chamber was off for approximately 12 hours. Since the temperature was below the ambient temperature and there was no irradiation during this period, we assumed that the chemical reaction in this period was inhibited. The temperatures recorded in this period were not used in the statistical analysis. The pH values of the dosed pH 7.0 buffer solution and pH 7.0 buffered SHW solutions at the experimental start and experimental termination were 7.0.

Irradiance Spectra:
The irradiance (photon flux) spectra from xenon arc lamp in the SUNTEST CPS+ chamber measured with a spectroradiometer before and after the study. Conversion factor of artificial sunlight days to natural summer sunlight was calculated to be 1.61 i.e., one day of artificial irradiation was equivalent to 1.61 days of the average natural summer sunlight irradiation at the latitude 30 °N - 50 °N.

Recovery, Rate Constants, and Half-Life Calculations of test substance:
Concentrations of test substance in irradiated SHW and pH 7.0 buffered test solutions calculated based on the equivalent analytical concentrations of 6:2 FTOH. It was considered that 1H-PFHx, 6:2 FTO, PFHxA, PFHpA, 6:2 FTCA, and 6:2 FTUCA were obtained by transformation of 6:2 FTOH. Concentration of test substance in SHW gradually decreased from the initial 99.6% of the nominal on Day 0 to 93.7%-95.1% of the nominal on Day 19. Concentration of test substance in pH 7.0 buffer decreased flam the initial 99.6%-99.7% of the nominal on Day 0 to 92.1%-94% of the nominal on Day 19. The difference between concentrations of remaining test substance in SHW and pH 7.0 buffer solution during 19 days of irradiation was insignificant. Thus, indirect photolysis played a less important role in test substance photo degradation than direct photolysis. Presence of humic acid might provide some quenching effect on the phototransformation of test substance.
Concentrations of test substance in the dark controls of SHW and pH 7.0 buffered test solutions remained constant indicating that there was no chemical transformation of the test substance in these systems. So, correction on dark control transformation was not included in the calculation of the photolysis half-life or irradiated samples.
Photolysis rate constant calculated using first-order kinetic regression of the data for the irradiated SHW samples from days 0 to 19 was 0.0028/day. Based on this value of the rate constant, DTSO and DT90 of test substance under xenon arc light irradiation were 245 days and 813 days, respectively, corresponding to 875 and 2907 days of average summer solar it-radiation at horizontal surface at latitude 30 °N to 50 °N in a natural water environment. Both values are beyond the duration of the study and should be considered as extrapolated.

The rate constant for phototransformation of irradiated pH 7.0 buffer samples was 0.0034/day. DT50 and DT90 values of test substance in pH 7.0 buffer under xenon arc light irradiation were 201 days and 669 days, respectively, corresponding to 721 and 2394 days of average summer solar irradiation at horizontal surface at latitude 30 °N to 50 °N. These values are extrapolated beyond the duration of the study. Therefore, test substance is considered as "photoinert" ("less than 20 percent photoreaction occurs at the end of 16-day irradiation".
Results with reference substance:
Recoveries of Degradation Products in the Test Vessels
Dark Control: Concentrations of potential photo degradation products of test substance (6:2 FTOH, 1H PFHx, 6:2 FTO, PFHxA, PFHpA, 6:2 FTCA, and 6:2 FTUCA) in the dark control pH 7.0 buffer solution and SHW solutions before and after incubation were negligible (below LOQ) and did not change at all incubation periods. Thus test substance was considered to be hydrolytically stable in both tested matrices and loss of the test substance in irradiated samples could be caused only by photolytic transformation.

Light Exposure:
Concentrations of the major photo degradation product 6:2 FTOH and its derivatives (PFHx, 6:2 FTO, PFHxA, PFHpA, 6:2 FTCA, and 6:2 FTUCA) in irradiated pH 7.0 buffer and SHW samples treated with test substance. Total concentrations of the seven potential photo degradation products in the irradiated pH 7.0 buffer samples slightly increased from (he initial "not detected" on Day 0 to 0.000934-0.0115 µm% on Day 4, and further slightly increased to 0.0151-0.926 µm% on Day 18.
The recoveries of the potential photo degradation products in the irradiated SHW samples gradually increased from the initial "not detected" on Day 0 to 4.95-5.82 µm% on Day 18. Major photo degradation product in the irradiated SHW samples treated with test substance was 6:2 FTOH, at concentration of approximately 4.76-5.61 µm% on Day 18.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Conclusions:
The half-life (DT50) of test substance at solar irradiation at horizontal surface in synthetic natural water and pH 7.0 buffer was 875 days and 721 days, respectively. Therefore, test substance is considered as "photoinert".
Executive summary:

Indirect Photolysis of test substance was assessed in pH 7.0 aqueous buffer solution and pH 7.0 buffered synthetic humic water. The polymer test substance was stable under dark control in both test media at all tested incubation periods, as monitored by assessment of concentrations of 6:2 FTOH and its derivatives. Irradiation with artificial sunlight (xenon arc lamp) for 18.5 days (equivalent to 30 solar irradiation days) both in SHW and in pH 7.0 phosphate buffer resulted in photolytical transformation of test substance polymer into FTOH and its derivatives. Phototransformation rate corresponds to a half-life of 875 days in natural water bodies or 721 days in pH 7.0 aqueous buffer (the values are extrapolated beyond the test period). The test substance was therefore considered photolytically stable in natural water at approximately 25°C.