Registration Dossier

Environmental fate & pathways

Phototransformation in water

Currently viewing:

Administrative data

Link to relevant study record(s)

Reference
Endpoint:
phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
06 November 2018 to 25 January 2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Study type:
direct photolysis
Qualifier:
according to
Guideline:
OECD Guideline 316 (Phototransformation of Chemicals in Water - Direct Photolysis)
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
Identification: [carbonyl-14C]Omnirad 379
Physical Description: Pale yellow solution in acetonitrile
Radiochemical purity: 99.3%
Chemical purity: 98.6%
Specific activity: 3.45 MBq/mg (1317 MBq/mmol)
Test item storage: In freezer (≤ -15°C) protected from light
Supplier: Selcia Limited, Fyfield Business & Research park, Fyfield Road, Ongar, Essex, CM5 OGS, UK

Radiolabelling:
yes
Remarks:
[carbonyl-14C]Omnirad 379
Analytical method:
high-performance liquid chromatography
Details on sampling:
- Sampling intervals for the parent/transformation products: Samples were taken at twelve time intervals, including t=0
- Sampling methods for the volatile compounds, if any: Polyurethane foam (PUF) traps were used for CO2
- Sampling intervals/times for pH measurements: The pH remained stable during the incubation period and ranged between 3.9 and 4.1 at pH 4, and between 6.9 and 7.2 at pH 7.
- Other observation, if any (e.g.: precipitation, color change etc.): No turbidity was observed in the BHI medium at all sampling points for irradiated solutions and dark controls. These negative readings indicate all vessels were sterile at the time of sampling
Buffers:
Acetate buffer pH 4, 0.01 M Solution of 0.2460 gram sodium acetate in 300 mL water and 0.9052 gram acetic acid in 1500 mL water combined
Phosphate buffer pH 7, 0.01 M Solution of 2.7304 gram dihydrogen phosphate in 1000 mL water, adjusted to pH 7 using 1 M sodium hydroxide and made up to 2000 mL with water
Light source:
sunlight
Remarks:
Suntest CPS+ system (Atlas GmbH, Linsengericht, Germany), equipped with a xenon light source providing a maximum output of approximately 1.5 kW
Light spectrum: wavelength in nm:
> 250 - < 765
Details on light source:
Suntest CPS+ system (Atlas GmbH, Linsengericht, Germany), equipped with a xenon light source providing a maximum output of approximately 1.5 kW. The xenon light source is equipped with a quarts glass filter with IR reflective coating for heat reflection and a UV-filter for cut-off of wavelengths below 290 nm. The spectrum of the xenon light source simulates the spectrum of natural sunlight. Irradiance could be controlled between approximately 250 and 765 W/m2 in the 300-800 nm band. The intensity of the xenon light source at the position of the exposed test solutions was determined before the start and at the end of the photolytic degradation test, using a XenoCal irradiance sensor (Atlas GmbH). Light intensity was measured in the 300-400 nm band.
Details on test conditions:
Solutions of Omnirad 379 in 0.01 M buffer were irradiated in a Suntest CPS+ system (Atlas GmbH, Linsengericht, Germany), equipped with a xenon light source providing a maximum output of approximately 1.5 kW. The xenon light source is equipped with a quarts glass filter with IR reflective coating for heat reflection and a UV-filter for cut-off of wavelengths below 290 nm. The spectrum of the xenon light source simulates the spectrum of natural sunlight (Figure 2 in Appendix 3). Irradiance could be controlled between approximately 250 and 765 W/m2 in the 300-800 nm band.
Test solutions were irradiated in small irradiation vessels equipped with two traps; polyurethane foam for volatile organics, and soda lime for CO2. Vessels were closed with a quartz glass lid using vacuum grease (Figure 1). Vessels were placed on a cooling table connected to a flow-through cooling water system to allow adequate temperature control. The vessels were placed in a thin layer of glycerol to ensure good contact with the cooling plate.
Test item solutions, glassware, and trapping systems for the dark controls were identical to those for irradiated samples. Dark controls were placed in a water bath adjusted to a temperature of 25°C.

The intensity of the xenon light source at the position of the exposed test solutions was determined before the start and at the end of the photolytic degradation test, using a XenoCal irradiance sensor (Atlas GmbH). Light intensity was measured in the 300-400 nm band.

All glassware was sterilised prior to use at 160°C for 3 hours. Buffer solutions were sterilised at 121°C for 20 min prior to use.
Sterility and pH of the test solutions were determined at each sampling point. For the sterility test, 0.1 mL of test solution was added to approximately 3 mL of sterile BHI medium and the mixture was incubated for at least two days at 37°C. Absence of turbidity (observed visually) was considered as proof for sterile conditions.
The pH was measured in approximately 3 mL aliquots taken from the test solutions (irradiated solution and dark control).
Spike solutions were prepared by dissolving 14C-labelled Omnirad 379 in acetonitrile. Solutions to spike pH 4 and pH 7 buffers contained 522 mg/L (1.8 MBq/mL). Concentration of Omnirad 379 in spike solutions was based upon analysis by LSC (RSD 0.3-1.7%).
Spike solutions were prepared at the start of the experiment and were analysed by HPLC. Spiking took place by addition of 156 µL and 39 µL of spike solution to vessels containing a known volume of approximately 18 mL buffer pH4 and pH 7, respectively. The spike volume was chosen based on a maximum organic solvent content of 1%. Final concentrations of Omnirad 379 were approximately 4.64 mg/L (pH 4) and 1.16 mg/L (pH 7).
Irradiation vessels were closed with a quartz glass lid using vacuum grease. Solid traps for CO2 were added (see Figure 1). Vessels were placed in the Suntest system at approximately 25°C. One additional vessel containing 18 mL buffer but without test item was placed in the Suntest chamber to monitor the temperature. Hereto, a thermocouple was inserted in the solution within the vessel (see Figure 1). The surface area of test solution exposed to the light source was 10.3 cm2. Distance of test solution surface to the light source was approximately 19 cm.
Control vessels (also closed with a quartz glass lid, containing test item, and equipped with a trapping system) were placed in the dark in a water bath at approximately 25°C. One additional vessel containing 18 mL buffer without test item was used for temperature monitoring by means of a thermocouple inserted in the solution.
At each pH, two vessels containing test item were analysed immediately after preparation (see section 4.9.3) and served as the t=0 sample.
Samples were taken at twelve time intervals, including t=0. For a selected number of sampling points, the weight of the test solution was determined to account for loss of volume due to evaporation. Radioactivity in three weighed 1 mL subsamples was determined by LSC. Test solution was decanted from the test vessel and partially treated for further analysis.
If radioactivity recovered from test solutions was less than 95% of applied, radioactivity in the traps was analysed. Polyurethane foam (PUF) traps were extracted by vortexing for one minute with a weighed 10 mL acetonitrile aliquot. Total radioactivity was determined by LSC of a 1 mL subsample. Soda lime granules were transferred to a 3-neck round-bottom flask, connected to traps containing approximately 100 mL 2M NaOH. Thereafter, 2M HCl was added to the soda lime. Humidified air was passed over the continuously stirred soda lime mixture and was led through the traps until all soda lime had dissolved. Radioactivity in the weighed traps and acidified soda lime mixture was determined by LSC of a weighed 1 mL subsample.
In case of an incomplete mass balance, test vessels of irradiated buffer solutions were rinsed with a two weighed aliquots (10 mL in total) of acetonitrile. Total radioactivity in the pooled rinsate was determined by LSC of a weighed 1 mL subsample.
Duration:
14 d
Temp.:
21.4 °C
Initial conc. measured:
4 other: pH
Duration:
14 d
Temp.:
24.2 °C
Initial conc. measured:
7 other: pH
Reference substance:
no
Dark controls:
yes
Computational methods:
The DT50 and DT90 values were calculated using the amounts of parent compound as determined by LC-RAD. Data for the parent and degradation products were fitted to the single first order kinetics (SFO; see Figure 5) and to the first order multi compartment/Gustafson and Holden model
If the SFO fit was acceptable and better than the FOMC fit (based on visual assessment, t-test, and χ2 test), no further work was done. If the SFO fit was not acceptable or the FOMC fit was better, the data were also fitted to the hockey stick model and the double first-order in parallel model Optimisations were performed using CAKE version 3.2.
Two first order rate constants can be calculated: kirr for the irradiated solutions and kdark for the dark controls. The photolytic first order rate constant, kphot, and the photolytic half-life can be calculated from kirr and kdark, using Equation 1.
k_phot=k_irr-k_dark
The spectral distribution of the xenon lamp simulates the solar spectral distribution in the range of 290-800 nm (Figure 2). This wavelength band is the most relevant range for photolytic degradation reactions.
The following data were available:
Spectral distribution of xenon lamp (W/m2 versus wavelength) from 290 nm to 800 nm, with a 2.5 nm interval (Table 11).
Actual xenon light intensity in the range of 300-400 nm (see section 8.2.2).
Actual xenon light intensity (W_sample^xenon) was corrected for the presence of a quartz plate covering the samples (Cquartz) and for the position of the samples under the xenon light source (Fposition X), using Equation 2.
W_sample^xenon=C_quartz×F_(position X)×W_ref^xenon (Equation 2)
Correction factor for the quartz plate Cquartz was 0.958. The factor Fposition X corrects for the position of the samples under the xenon light source and ranges from 1.041 to 1.132. These factors were determined in Test Facility Study No. 385166 under GLP [1]. Because light intensity varied for each irradiated test solution, exposure to the standardized xenon lamp intensity (taverage) was calculated from incubation time (tincubation) according to Equation 3.
t_average=(W_sample^xenon)/(W_average^xenon )×t_incubation (Equation 3)
Furthermore, W_sample^xenon was compared with intensity of natural sunlight (section 8.2.9).
For calculation of quantum yield, light intensity in Watt/m2 (W()) of the xenon light source for each wavelength interval (with center  and band width 2.5 nm) as given by the supplier (Table 11) was converted to units of photons * s-1 * m-2 (Irt()), using Equation 4.
I_rt (λ)=(W(λ)×λ)/(h×c)×〖10〗^(-9) (Equation 4)
With h: Planck constant = 6.626 * 10-34 J * s
: wavelength (nm)
c: speed of light = 2.998 * 108 m * s-1
Watt: J * s-1
Photon energy = h with : frequency (in s-1), and  = c/

Irt() was corrected for the actual light intensity received by the samples using Equation 5.
I_0 (λ)=(W_sample^xenon)/(W_table^xenon )×I_rt (λ) (Equation 5)
With Subscript 0 denoting actual incident light
W_table^xenon: xenon light intensity as given in the manufacturer table (Table 11), summated over 300 to 400 nm (Watt/m2)
W_sample^xenon: xenon light intensity as determined using the XenoCal UV meter, summated over 300 to 400 nm (Watt/m2)
The molar absorption coefficient T() (in L * mol-1 * cm-1) was calculated from UV/VIS spectral data, distance of light through the test solution (in cm), and concentration of the test solution (in mol * L-1), using Equation 6.
A=log⁡[(I_0 (λ))/(I_t^T (λ) )]=log⁡[(W_0 (λ))/(W_t^T (λ) )]=ε^T (λ)×C×d (Equation 6)
With A = absorbance
I0() = incident photons * s-1 * m-2
It() = transmitted photons * s-1 * m-2
d = thickness of the test item solution (cm)
C = concentration of test item (analysis UV/VIS spectrum) (mol * L-1)
εT(λ) = extinction coefficient of test item at wavelength λ
The superscript T denotes test item solution
The subscript t denotes transmitted light intensity
The subscript 0 denotes incident light intensity
The fraction of incident photons absorbed by the test item in each spectral band, with center  and width 2.5 nm, was calculated for the range 290-400 nm using Equation 7 and 8.
I_t^T (λ)=I_0×〖10〗^(-ε^A (λ)×C_T×d) (Equation 7)
I_a^T (λ)=I_0 (λ)-I_t^T (λ) (Equation 8)
With I_a^T (λ) = absorbed photons * s-1 * m-2
I0(λ) = incident photons * s-1 * m-2
The subscript a denotes absorbed light intensity
The number of photons absorbed per second per m2 (I_a^T (λ)) was converted to number of photons absorbed by the test solution per second (i_a^T (λ)) using Equation 9.
i_a^T (λ)=I_a^T (λ)×S (Equation 9)
With S = surface of test solution exposed (0.00103 m2 for each sample)
Parameter:
max epsilon
Value:
18 400 1/cm dm³ 1/mol
Remarks:
At 352.5 nm for pH 4 using 0.066mM
Parameter:
max epsilon
Value:
15 000 1/cm dm³ 1/mol
Remarks:
At 357.5 nm pH7 0.066mM
Key result
% Degr.:
100
Sampling time:
3 h
Test condition:
pH4
Key result
% Degr.:
100
Sampling time:
1 h
Test condition:
pH7
Key result
DT50:
0.019 d
Test condition:
pH4
Key result
DT50:
< 0.012 d
Test condition:
pH7
Predicted environmental photolytic half-life:
Upon incubation under simulated sunlight, Omnirad 379 degraded to 0% (pH 4 and pH 7) after an incubation time of 3 hours and 1 hour, respectively, corresponding to approximately 6.5 and 2.2 hours of natural sunlight
Transformation products:
yes
No.:
#3
Validity criteria fulfilled:
yes
Conclusions:
Upon incubation under simulated sunlight, Omnirad 379 degraded to 0% (pH 4 and pH 7) after an incubation time of 3 hours and 1 hour, respectively, corresponding to approximately 6.5 and 2.2 hours of natural sunlight. Seven major photolytic degradation products were detected, which exceeded 10% of applied radioactivity.
The degradation process was very complex and consisted of combinations of cleavage, hydrolysis, desaturation, oxidation and reduction and eventual breakdown to CO2.
Executive summary:

Upon incubation under simulated sunlight, Omnirad 379 degraded to 0% (pH 4 and pH 7) after an incubation time of 3 hours and 1 hour, respectively, corresponding to approximately 6.5 and 2.2 hours of natural sunlight. Seven major photolytic degradation products were detected, which exceeded 10% of applied radioactivity. From the identification of the seven major photolytic degradation products (M-1, M-2, M-3, M-5, M-6, M-7 and M-9) detected during photochemical degradation of Omnirad 379 in water (Charles River Den Bosch Study 20153931), it was observed using a LC-PDA-(RAD)MSn method that several degradation products were co-eluting at the retention time of M-2 (coded M-2a/b/c), M-3 (coded M-3a/b), M-4 (coded M-4a/b/c/d/e/f/g) and M-5 (coded M-5a/b) whereas one degradation product was observe at the retention time of M-1, M-6 and M-7. The identification of degradation product M-9 was not possible due to a too low amount of radioactivity.  Due to no or very limited MS data it was not possible to propose structures for five degradation products with a low MS intensity (i.e., M-2c, M-4e, M-4f, M-4g and M-5b).  Based on accurate masses and MSn fragmentations, molecular structures were proposed for thirteen degradation products with a medium or high MS intensity (i.e., M-1, M-2a, M-2b, M-3a, M-3b, M-4a, M-4b, M-4c, M-4d, M-5a, M-5b, M-6 and M-7). The proposed structures of each are in the attached background material JPEG.

M-1 : Retention time 11.5 mins, C1014CH12NO5+

Based on the accurate mass m/z 240.074 is most likely the loss of N,N-dimethyl-1-(p-tolyl)butan-2-amine in combination with a desaturation (+H2) and 3 oxidations (+3 O atoms).  

M-2a Retention time 13.7 mins, C1014CH14NO3+

Based on the accurate mass m/z 210.100 is most likely the result of hydrolysis of the 14C atom, and thus the loss of N,N-dimethyl-1-(p-tolyl)butan-2-amine.

M-2b Retention time 13.7 mins, C2314CH33N2O 2+

Based on the accurate mass m/z 383.257 this molecule is comparable to the parent compound.  However, as the retention time of M-2b is slightly different than the retention time of the parent compound, this degradation product was further investigated.   Based on the molecular formula and the loss of C2H5N, the molecule is most likely desaturated at the dimethylamine and reduced at the C-moiety

M-2c Retention time 13.7 mins, C2314CH33N2O3+

Based on the accurate mass m/z 399.252 is most likely the result of an oxidation of the parent compound

M-3a Retention time 14.8 mins, C1014CH14NO2+

Based on the accurate mass m/z 194.105 is most likely the result of cleavage of the moiety containing the AB-ring and the moiety containing the C-ring to give 4-(4-Morpholinyl)benzaldehyde (CAS 1204 -86 -0).

M-3b Retention time 15.0 mins, C2114CH26NO3+

Based on the accurate mass m/z 354.193 is most likely the result of the loss of the dimethylamine (C2H7N) moiety resulting in a desaturation in combination with an oxidation.  

M4a Retention time 21.4 mins, C2114CH26NO3+

Based on the accurate mass m/z 354.193 is most likely the result of the result of the loss of the NH dimethyl moiety in combination with an oxidation

M4b, Retention time 21.6 mins, C2114CH24NO3+

Based on the accurate mass m/z 352.178 is most likely the result of the loss of dimethylamine (C2H7N) moiety resulting in a desaturation in combination with a desaturation and oxidation.  

M4c, Retention time 21.6 mins, C2114CH24NO4+

Based on the accurate mass m/z 368.173 is most likely the result of the loss of dimethylamine (C2H7N) moiety resulting in a desaturation in combination with a carboxylation.

M4d, Retention time 21.6 mins, C2114CH24NO4+

Based on the accurate mass m/z 368.173 is most likely the result of the loss of dimethylamine (C2H7N) moiety resulting in a desaturation in combination with desaturation and 2 times oxidation.  

M5a, Retention time 22.3, C2114CH28NO3+

Based on the accurate mass m/z 356.209 is most likely the result of loss of NH dimethyl moiety in combination with an oxidation

M5b, Retention time 22.3 mins, C2314CH35N2O3+

Based on the accurate mass m/z 401.267 is most likely the result of an oxidation in combination with a desaturation of a double bond of the parent compound

M6, Retention time 23.4 mins, C2114CH26NO2+

Based on the accurate mass m/z 338.198 is most likely the loss of dimethylamine (C2H7N) resulting in the formation of a desaturation.  

M7, Retention time 24.4 mins, C2114CH26NO2+

Based on the accurate mass m/z 338.198 is most likely the loss of dimethylamine (C2H7N) resulting in the formation of a desaturation

The degradation process was very complex and consisted of combinations of cleavage, hydrolysis, desaturation, oxidation and reduction and eventual breakdown to CO2.

At pH 4, degradation product M-1 increased to a maximum of 24.5% of applied radioactivity after an incubation time of 2 days, after which concentrations decreased to 3.4% of applied radioactivity after an incubation time of 14 days. Degradation product M-2, M- 5, M-6, and M-7 all increased to their maximum concentration within 24 hours of incubation, and decreased to 0% of applied radioactivity by the end of the incubation period.

At pH 7, degradation product M-1 increased to a maximum of 13.5% of applied radioactivity after an incubation time of 2 days, after which concentrations decreased to 3.8% of applied radioactivity after an incubation time of 14 days. Degradation product M-8 increased to a maximum of 9.9% of applied radioactivity after an incubation time of 1 day, after which concentrations decreased to 8.1% of applied radioactivity after an incubation time of 14 days. Degradation product M-9 increased to a maximum of 19.5% of applied radioactivity after an incubation time of 7 days, after which concentrations decreased to 12.8% of applied radioactivity after an incubation time of 14 days. Degradation product M-2, M-3, M-5, and M-6 all increased to their maximum concentration within 24 hours of incubation, and decreased to 0% of applied radioactivity by the end of the incubation period. One degradation product (M-3) could be identified as 4-(4-morpholinyl)benzaldehyde by co- chromatography against reference standard AS1842.

Significant amounts of CO2 were formed in a few samples (up to 27.4% and 20.6% of applied radioactivity at pH 4 and pH 7, respectively). Negligible amounts of organic volatiles were detected (<0.3% of applied radioactivity) in the PUF traps. Recovery from vessel rinsates at pH 4 increased to 6.7% of applied radioactivity after an incubation time of 3 hours, and then gradually declined to <0.1% after 14 days of incubation. At pH 7, recovery from vessel rinsates was highest at the start of incubation, with up to 29.7% of applied radioactivity. This gradually decreased with incubation time, to <0.1% after 14 days of incubation, except for the dark controls where recovery was still approximately 20% (on average) after 14 days of incubation.

Degradation was also observed in the dark control samples. After an incubation time of 14 days, 91.4% and 88.2% was recovered as parent at pH 4 and pH 7, respectively. No major degradation products were formed in the dark controls. The degradation rates of Omnirad 379 in the dark and in natural sunlight (photolytic degradation rate) are summarised in the table below.

Photolytic Degradation Rate of Omnirad 379

   

DT50, dark [days]

 

DT50, phot [days]

 

DT90, dark [days]

 

DT90, phot [days]

 pH4  >10,000  0.019  >10,000  0.062
 pH7  229  <0.012  762  0.036

Description of key information

Study conducted to internationally recognised testing guideline with GLP

Key value for chemical safety assessment

Half-life in water:
0.012 d

Additional information

Upon incubation under simulated sunlight, Omnirad 379 degraded to 0% (pH 4 and pH 7) after an incubation time of 3 hours and 1 hour, respectively, corresponding to approximately 6.5 and 2.2 hours of natural sunlight. Seven major photolytic degradation products were detected, which exceeded 10% of applied radioactivity.

Photolytic Degradation Rate of Omnirad 379

   

DT50, dark [days]

 

DT50, phot [days]

 

DT90, dark [days]

 

DT90, phot [days]

 pH4  >10,000  0.019  >10,000  0.062
 pH7  229  <0.012  762  0.036