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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
experimental phase : January 2020 - April 2021
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on source and properties of surface water:
The test water and sediment was collected from Brandywine Creek, Pennsylvania on 30 March 2020, 12 May 2020, and 22 June 2020. The collection date, temperature, dissolved oxygen content and pH at collection are presented in section "Any other information on materials and methods incl. tables". The water was transported in a cool, sealed container with enough headspace to provide access to air and arrived at Eurofins on 1 April 2020, 13 May 2020, and 24 June 2020. The characterization of the water and sediment are also detailed in section "Any other information on materials and methods incl. tables". The water and sediment characterization was conducted off-site at Agvise Laboratories, Inc. (Northwood, North Dakota).
For each collection, the water upon arrival was filtered through a 0.2 mm sieve and the sediment was filtered through a 2 mm sieve to remove coarse particulate matter and debris. One gram of Brandywine Creek sediment was transferred to each one liter of Brandywine Creek water used, creating water amended with sediment. Approximately 100 mL of water amended with sediment was measured out using a graduated cylinder and dispensed into 250-mL amber bottles for the high dose, low dose, and reference samples. For the sterile samples, one liter of water amended with sediment was placed in the autoclave for 30 minutes at 250°F and 15 psi (0.10 MPa) to be sterilized. 100 mL of sterilized water amended with sediment was dispensed using sterile techniques into 250-mL sterilized amber glass bottles (autoclaved at 250°F and 15 psi (0.10 MPa). The pH and dissolved oxygen content of the filtered water was measured before use in the study and prior to sampling at each time interval.

Total Organic Carbon of Test System:
The water sample was analyzed for total organic carbon (TOC), at the beginning and end of incubation of the first experimental set (o,m-DBT), at the end of the second experimental set (0,0-DTPM), and at the beginning and end of incubation of the third experimental set (tested impurity), during the study, expressed in ppm.
Details on source and properties of sediment:
See section 'Details on source and properties of surface water'
Duration of test (contact time):
60 d
Initial conc.:
9.9 µg/L
Based on:
other: [14C] tested impurity
Initial conc.:
108.2 µg/L
Based on:
other: [14C] tested impurity
Initial conc.:
10.5 µg/L
Based on:
test mat.
Remarks:
[phenyl-U-14C] o,o-DTPM
Initial conc.:
102.2 µg/L
Based on:
test mat.
Remarks:
[phenyl-U-14C] o,o-DTPM
Initial conc.:
10.3 µg/L
Based on:
test mat.
Remarks:
[phenyl-U-14C] o,m-DBT
Initial conc.:
102.2 µg/L
Based on:
test mat.
Remarks:
[phenyl-U-14C] o,m-DBT
Parameter followed for biodegradation estimation:
radiochem. meas.
test mat. analysis
Details on study design:
Experimental Design and Description of Setup:
The high-dose and low-dose viable samples were connected to trapping vessels for continuous trapping throughout the study. A peristaltic pump was used to draw ambient air first through a vial containing deionized water to moisturize the air, followed by the sample container fitted with a foam plug in the sample top/ neck of the bottle, and then to a series of traps containing a foam plug trap to collect organic volatiles and two caustic traps (10% aqueous sodium hydroxide) to collect 14C-carbon dioxide. The samples were connected via Teflon tubing threaded through the septum caps and connected to manifolds. Trap solutions and foam plug traps were housed in glass vials (40 mL capacity) fitted with open top caps with Teflon-lined silicon septa through which the Teflon tubing was threaded in the same fashion as the samples. Samples were placed in a constant temperature room maintained at 12 ± 2°C during the incubation period. Sample bottles were placed on an orbital shaker for continuous gentle shaking during the incubation period. The temperature of the constant temperature room was continuously monitored with a REES temperature monitoring system.
The setup of the reference control samples (dosed with [14C]benzoic acid) was similar to that of the high-dose/low-dose viable samples (a foam plug trap and two 10% aqueous sodium hydroxide traps), however foam plugs were not placed at the neck of the bottle for the reference control samples.
For sterile sample set, all glassware was autoclaved at 250°F and 15 psi (0.10 MPa) for 20 minutes prior to use. The sterile samples were prepared with a foam plug in the sample top/ neck of the bottle and no traps were required or connected for volatile/CO2 collection. Sterile samples were placed on an orbital shaker in a constant temperature room maintained at 12 ± 2°C during the incubation period.
The untreated incubated samples were capped with foam plugs in the bottle neck. Untreated samples were placed on an orbital shaker and incubated in a constant temperature room maintained at 12 ± 2°C during the incubation period. The temperature of the constant temperature room was continuously monitored with a Rees temperature monitoring system.

* Application Procedure
Aliquots (3 × 20-100 µL) of the dose solutions were taken for radioassay pre, mid and post dosing process for the high and low doses. Aliquots (3 x 20 µL) of the dose solutions were taken for radioassay at least before and after the dosing process for the sterile (high dose) and reference doses. All aliquots were radioassayed via LSC, to determine the actual dose rates and to confirm homogeneity of the dosing solutions during the application procedure.
- High-Dose Set
A total of 16 aqueous viable samples were prepared and dosed as the high-dose set for each radiolabel. The target dose rate for this set was 100 µg/L. Each sample (100 mL) was dosed with 100 µL of the High Concentration dose solution (above) delivered in a circular motion directly into the aqueous sample using a 100 µL glass syringe. The final dose rate of DBT test substance in high concentration samples was 102.2 µg/L ([phenyl-U-14C]o,m-DBT and [phenyl-U-14C]o,o-DTPM sets) and 108.2 µg/L ([14C] tested impurity set).
- Low-Dose Set
A total of 16 aqueous viable samples were prepared and dosed as the low-dose set for each radiolabel. The target dose rate for this set was 10 µg/L. Each sample (100 mL) was dosed with 100 µL of the Low Concentration dose solution (above) delivered in a circular motion directly into the aqueous sample using a 100 µL glass syringe. The final dose rate of DBT test substance in low concentration samples was 10.3 µg/L ([phenyl-U-14C]o,m-DBT set), 10.5 µg/L ([phenyl-U-14C]o,o-DTPM set), and 9.9 µg/L ([14C] tested impurity set).
- Sterile Set
A total of 8 aqueous sterile samples were prepared and dosed as the sterile set for each radiolabel. The target dose rate for this set was 100 µg/L. The sterile sample (100 mL) was dosed with 100 µL of the high concentration dose solution (above) was delivered in a circular motion directly into the aqueous sample using a 100 µL glass syringe. The final dose rate of DBT test substance in sterile samples was 102.2 µg/L ([phenyl-U-14C]o,m-DBT and [phenyl-U-14C]o,o-DTPM sets) and 106.1 µg/L ([14C] tested impurity set).
- Control Substance Set
A total of 6 aqueous viable samples were prepared and dosed as the control set for each radiolabel. The target dose rate for this set was 100 µg/L. Each sample (100 mL) was dosed with 100 µL of the control dose solution (above) delivered in a circular motion directly into the aqueous sample using a 100 µL glass syringe. The final dose rate of benzoic acid in reference (control) samples was 102.1 µg/L ([phenyl-U-14C]o,m-DBT set), 102.2 µg/L ([phenyl-U-14C]o,o-DTPM set), and 11.8 µg/L ([14C] tested impurity set, isotopically diluted).

* Experimental Conditions and Monitoring
Following application, viable samples and control substance samples were placed on orbital shakers, connected to their respective traps for volatiles, and kept in the constant temperature room maintained at 12 ± 2 °C in the dark during the study period, . Sterile samples were not connected to traps for volatiles since no degradation was expected in these samples.

* Sampling Intervals and Collection
High- and low-dose samples were sacrificed at 0, 7, 14, 30, 42, and 63 DAT (o,m-DBT), 0, 7, 14, 30, 42, and 62 DAT (o,o-DTPM), and 0, 7, 14, 29, 42, and 63 DAT ([14C] tested impurity). Sterile samples were sacrificed at 7, 30, and 63 DAT ( o,m-DBT), 7, 30, and 62 DAT (o,o-DTPM), and 7, 29, and 63 DAT ([14C] tested impurity). Benzoic acid control samples were sacrificed at 7 and 14 DAT. Duplicate samples for each set were removed as applicable from the constant temperature room at each time point.
Reference substance:
benzoic acid, sodium salt
Key result
Compartment:
natural water: freshwater
DT50:
32.8 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: [14C] tested impurity
Key result
Compartment:
natural water: freshwater
DT50:
> 10 000 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: [phenyl-U-14C]o,o-DTPM
Key result
Compartment:
natural water: freshwater
DT50:
56.9 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: [phenyl-U-14C]o,m-DBT
Transformation products:
yes
Details on transformation products:
Degradation products were observed throughout the study in two out of the three labels. Unknown degradates at ~10.00 min and ~14.00 min represented a maximum of 21.2% AR and 22.1% AR (high-dose) ([phenyl-U-14C] o,m-DBT) at the end of the incubation period. Unknown degradates at ~14.4 min represented a maximum of 27.9% AR (high-dose) ([14C] tested impurity) at the end of the incubation period.
Unknown metabolites were detected in [phenyl-U-14C]o,m-DBT and the [14C] tested impurity and was analyzed by LC-MS using APPI/APCI to determine metabolite profiles and identify prominent metabolites ( See details in Appendix 12).

Proposed Degradation Pathway of DBT
The degradation pathway of DBT in natural water with amended solids under aerobic conditions is presented in Figure 9 in the section "attached background material".
Details on results:
* Radiochemical Purity of Test and Control Substances
The radiochemical purity of [14C]DBT in the dose solution following the application processes was determined to be 100.0% for all three radiolabels, confirming the stability of the test substance during application. The purity of the [14C]benzoic acid dose solution following application processes was determined to be 100.0% for all three radiolabel sets.
The homogeneity of the dose solution during the dosing procedure was confirmed by radioassay of aliquots of the dose solution taken before and after application. The relative standard deviations for these aliquots were = 1.36%.

* Properties of Test System
Dissolved oxygen (DO) content measurements ranged from an average of 8.87 to 10.96 ppm for the high- and low-dose samples across the three labels (o,m-DBT, o,o-DTPM, and tested impurity), demonstrating that the test systems were maintained under aerobic conditions throughout the study. pH measurements ranged from an average of 7.00 to 7.99 for the high- and low-dose samples across the three labels (o,m-DBT, o,o-DTPM, and tested impurity). See details in Table 4 in the section "Attached background material".
All samples were incubated at 12 ± 2°C in a temperature controlled room throughout the study.

* Microbial Activity
The control samples were treated with [14C]benzoic acid at a concentration of 102.1 µg/L ([phenyl-U-14C]o,m-DBT set), 102.2 µg/L ([phenyl-U-14C]o,o-DTPM set), and 10.8 µg/L ([14C] tested impurity set, isotopically diluted). Duplicate samples were sacrificed after 7 and 14 days of incubation. Results showed average conversion of = 77.3% of the radiocarbon to 14CO2 (recovered in NaOH traps) after 14 days of incubation, demonstrating that the microbial activity of the water used in the study was sufficient to conduct the test.

* Mass Balance
Ranges of averaged recoveries are presented below.

Range of Averaged Recoveries (% AR)
Sample Set High Dose Low Dose Sterile
[phenyl-U-14C]o,m-DBT set 92.4 – 97.8 93.4 – 98.6 98.9 – 106.0
[phenyl-U-14C]o,o-DTPM set 94.3 – 102.7 91.3 – 104.8 93.4 – 100.2
[14C] tested impurity set 95.1 – 103.4 93.6 – 98.6 99.6 – 103.7

- [phenyl-U-14C]o,m-DBT set
Most of the radiocarbon was recovered in the aqueous samples for all samples tested. Radiocarbon in the water layers represented an average of 75.3 to 85.9% AR of dose in high dose and 82.0 to 90.4% AR of dose in sterile samples throughout the study. In low dose samples, radiocarbon in the water layers represented and average of 75.3 to 89.4% AR throughout the study.
Radiocarbon average recoveries in the organic rinse represented = 12.4% of the applied dose for all samples tested.Radiocarbon average recoveries in the foam plug neck and foam plug trap for organic volatiles represented = 21.2% of the applied dose for all samples tested(Table 6).
Recoveries in the NaOH traps as 14CO2 averaged a maximum of 2.2% AR (high-dose) and 4.6% AR (low-dose) at day 63.

- [phenyl-U-14C]o,o-DTPM set
Most of the radiocarbon was recovered in the aqueous samples for all samples tested. Radiocarbon in the water layers represented an average of 15.5 to 88.3% AR of dose in high dose and 36.7 to 72.9% AR of dose in sterile samples throughout the study. In low dose samples, radiocarbon in the water layers represented and average of 9.9 to 92.4% AR throughout the study.
Radiocarbon average recoveries in the organic rinse represented = 6.2% of the applied dose for all samples tested.Radiocarbon average recoveries in the foam plug neck and foam plug trap for organic volatiles represented = 87.0% of the applied dose for all samples tested (Table 7).
Recoveries in the NaOH traps as 14CO2 averaged a maximum of 0.3% AR (high-dose) at day 62 and 0.5% AR (low-dose) at day 30.

- [14C] Tested impurity set
Most of the radiocarbon was recovered in the aqueous samples for all samples tested. Radiocarbon in the water layers represented an average of 69.7 to 93.3% AR of dose in high dose and 91.3 to 93.8% AR of dose in sterile samples throughout the study. In low dose samples, radiocarbon in the water layers represented and average of 68.3 to 91.2% AR throughout the study.
Radiocarbon average recoveries in the organic rinse represented = 24.7% of the applied dose for all samples tested. Radiocarbon average recoveries in the foam plug neck and foam plug trap for organic volatiles represented = 7.5% of the applied dose for all samples tested (Table 8). Recoveries in the NaOH traps as 14CO2 averaged a maximum of 1.4% AR (high-dose) and 1.8% AR (low-dose) at day 63.

* Product Distribution Following Aerobic Mineralization of DBT in Surface Water
The distribution of radioactivity for DBT Test Substances for the study was determined by HPLC analysis of all the high-dose and sterile (HD) aqueous samples and selected bottle rinses and foam plug neck samples. Due to extremely low dpm present in the samples and comparable NaOH trap recoveries, the low dose samples were not analyzed by HPLC analysis. The high-dose samples are considered representative of both sets of samples. The product balance summary for the high-dose and sterile samples is presented in Table 9 ([phenyl-U-14C]o,m-DBT set), Table 10 ([phenyl-U-14C]o,o-DTPM set), and Table 11 ([14C] tested impurity set).
- [phenyl-U-14C]o,m-DBT set
Following 63 days of incubation, [phenyl-U-14C]o,m-DBT represented an average of 41.9% AR (0.043 ppm) and 96.0% (0.098 ppm) in the high-dose and sterile (HD) water layer, respectively. Unknown degradates were present, at approximately 10.00 min and 14.00 min, was observed in the high dose water layer samples and represented a maximum of 21.2% AR and 22.1% AR at the end of the incubation period (T63d). Unknown degradates were present in the sterile (HD) water layer and represented a maximum of 9.6% AR at ~14.0 min, at the end of the incubation period.
In the acetonitrile (ACN) bottle rinses, [phenyl-U-14C]o,m-DBT represented a maximum average of 12.4% AR at time 0 (high dose). In the foam plug neck extract, [phenyl-U-14C]o,m-DBT represented a maximum average of 15.7% AR (high dose) and 21.2% AR (sterile (HD)) at the end of the incubation period.
- [phenyl-U-14C]o,o-DTPM set
Following 62 days of incubation, [phenyl-U-14C]o,o-DTPM represented an average of 98.0% AR (0.100 ppm) and 96.9% (0.099 ppm) in the high-dose and sterile (HD) water layer, respectively. No unknown degradates were present.
In the acetonitrile (ACN) bottle rinses, [phenyl-U-14C]o,o-DTPM represented a maximum average of 6.1% AR at time 0 (high dose). In the foam plug neck extract, [phenyl-U-14C]o,o-DTPM represented a maximum average of 82.5% AR (high dose) and 60.3% AR (sterile (HD)) at the end of the incubation period (day 62).
- [14C] Tested impurity set
Following 63 days of incubation, the [14C] tested impurity represented an average of 16.7% AR (0.018 ppm) and 101.6% (0.108 ppm) in the high-dose and sterile (HD) water layer, respectively. An unknown degradation product, at approximately 14.45 min, was observed in the high dose water layer samples and represented a maximum average of 27.9% AR at the end of the incubation period.
In the MeOH bottle rinses, the [14C] tested impurity represented a maximum average of 20.0% AR at day 14 and averaged 5.9% AR at the end of the incubation period in the high dose, whereas in the sterile (HD) MeOH bottle rinses averaged 7.8% AR at the end of incubation (day 63). In the foam plug neck extract, the [14C] tested impurity represented a maximum average of 7.5% AR at day 14 and averaged 6.3% AR at the end of the incubation period (high dose).

* Confirmation of [14C]DBT and Metabolites
The identification of DBT ([phenyl-U-14C]o,m-DBT, [phenyl-U-14C]o,o-DTPM, and [14C] tested impurity was based on HPLC retention times and co-elution with the corresponding reference standards. Typical retention factor values (Rf) are presented in Table 1. The HPLC/ß-ram assignments of DBT ([phenyl-U-14C]o,m-DBT, [phenyl-U-14C]o,o-DTPM, and [14C] tested impurity in the surface water were confirmed by one-dimensional TLC analysis of representative samples with reference standards.

* Kinetic Analysis
The degradation rate of individual components of DBT in lake water with amended solids under aerobic conditions was determined based on the percent of applied dose in the water with amended solids relative to incubation time. DT50 and DT90 values were calculated using CAKE software version 3.3. The graphical degradation rates using the Single First Order (SFO), with additional models first-order multi-compartment (FOMC), double first-order parallel (DFOP), and hockey stick (HS) were used in order to obtain the best fit for the high dose concentration. Calculations for the best fit model of individual components ([phenyl-U-14C] o,m-DBT, [phenyl-U-14C] o,o-DTPM, and [14C] tested impurity of DBT kinetic calculations are presented in the section "kinetic evaluation". The statistics and DT50/DT90 values for the high dose of individual component of DBT are presented below, the best fit model is in bold. SFO was determined to be the best fit model in the high dose concentration of [phenyl-U-14C] o,m-DBT, and [phenyl-U-14C] o,o-DTPM, and [14C] tested impurity, determined by the lowest %error (with the exception of [14C] tested impurity best fit model was chosen based on other factors in comparison to the data) with DT50 values at 56.9 days ([phenyl-U-14C] o,m-DBT), >10,000 ([phenyl-U-14C] o,o-DTPM), and 32.8 days ([14C] tested impurity) and DT90 values at 189 days ([phenyl-U-14C] o,m-DBT), >10,000 ([phenyl-U-14C] o,o-DTPM), and 109 days ([14C] tested impurity).
Validity criteria fulfilled:
yes
Remarks:
The radiolabelled mass balance was range from 90% to 110% for all the three test materials.
Conclusions:
An aerobic mineralization study was conducted with [14C]DBT in the surface water from Brandywine creek, Pennsylvania for up to 63 days at two concentrations, (102.2 µg/L (high dose) and 10.3 µg/L (low dose) for [phenyl-U-14C] o,m-DBT, 102.2 µg/L (high dose) and 10.5 µg/L (low dose) for [phenyl-U-14C] o,o-DTPM, and 108.2 µg/L (high dose) and 9.9 µg/L (low dose) for [14C] tested impurity. The half-life of DBT during the study was determined as 56.9 days ([phenyl-U-14C] o,m-DBT), >10,000 days ([phenyl-U-14C] o,o-DTPM), and 32.8 days ([14C] tested impurity) (SFO model). Degradation products were observed throughout the study in two out of the three labels. Unknown degradates at ~10.00 min and ~14.00 min represented a maximum of 21.2% AR and 22.1% AR (high-dose) ([phenyl-U-14C] o,m-DBT) at the end of the incubation period. Unknown degradates at ~14.4 min represented a maximum of 27.9% AR (high-dose) ([14C] tested impurity) at the end of the incubation period.
Unknown metabolites were detected in [phenyl-U-14C]o,m-DBT and the [14C] tested impurity and was analyzed by LC-MS using APPI/APCI to determine metabolite profiles and identify prominent metabolites.
There was no significant difference in the 14CO2 production observed in high- and low-dose samples throughout the study demonstrating that the mineralization of DBT was not concentration dependent.
DBT exhibited moderate biodegradation in two out the three labels ([phenyl-U-14C] o,m-DBT and ([14C] tested impurity), whereas the third label ([phenyl-U-14C] o,o-DTPM) was stable with very little break down in the mineralization in surface water of the high dose concentration. DBT remained stable with very little biodegradation in the mineralization in surface water of sterile high dose for all three labels (([phenyl-U-14C] o,m-DBT, [phenyl-U-14C] o,o-DTPM, and the [14C] tested impurity.
Executive summary:

An aerobic mineralization preliminary and definitive study was conducted with [14C]DBT Test Substances using aerobic natural water with amended solids. Solubility was determined prior to conducting the definitive study for each test substance. In the definitive study, the water and sediment was collected from Brandywine Creek, Pennsylvania, USA. The test substance was applied at two concentrations: (102.2 µg/L (high dose) and 10.3 µg/L (low dose) for [phenyl-U-14C] o,m-DBT, 102.2 µg/L (high dose) and 10.5 µg/L (low dose) for [phenyl-U-14C] o,o-DTPM, and 108.2 µg/L (high dose) and 9.9 µg/L (low dose) for the [14C] tested impurity, and the samples were incubated in the dark on orbital shakers for constant agitation under aerobic conditions at 12 ± 2 °C for approximately 60 days. In addition, reference and sterile control samples were incubated at the same conditions to confirm the microbial activity of the test water with amended sediment and examine possible abiotic degradation, respectively. The reference control samples were treated with [14C]benzoic acid at a concentration of 102.2 µg/L for both [phenyl-U-14C] o,m-DBT and [phenyl-U-14C] o,o-DTPM. The reference control samples that were treated for the [14C] tested impurity samples were treated with [14C] benzoic acid isotopically diluted with benzoic acid cold standard and treated at a total dpm dosed of 10.8 µg.  The sterile control samples were treated with [14C]DBT at 102.1 µg/L ([phenyl-U-14C] o,m-DBT), 102.2 µg/L ([phenyl-U-14C] o,o-DTPM), and 106.1 µg/L ([14C] tested impurity). The test was performed in flow through systems allowing humidified air to pass over the sample headspace, foam plug neck and through the traps to collect volatile organic components (foam plug) and [14C]carbon dioxide (aqueous sodium hydroxide).  Sterile control samples were aerated in the same fashion with a foam plug neck but did not include traps for volatiles. At each sampling interval, the amount of radioactivity in the test water and traps for volatiles (if applicable) was determined by liquid scintillation counting (LSC), and the high-dose and sterile samples were analyzed by high-performance liquid chromatography (HPLC) coupled with β-ram detector.


The samples containing the reference substance [14C]benzoic acid were sacrificed after 7 and 14 days of incubation. The average evolution of 14CO2 observed after 14 days (≥ 85.9% AR ([phenyl-U-14C] o,m-DBT),  ≥ 87.9% AR ([phenyl-U-14C] o,o-DTPM), and ≥ 77.3% AR ([14C] tested impurity)) confirmed the microbial activity of the test water with amended solids.


Aliquots of the high-dose and low-dose samples containing [14C]DBT were analyzed after 0, 7, 14, 30, 42, and 63 days ([phenyl-U-14C] o,m-DBT), 0, 7, 14, 30, 42, and 62 days ([phenyl-U-14C] o,o-DTPM), and 0, 7, 14, 29, 42, and 62 days ([14C] tested impurity) of incubation. Mass balance was based on the sum of the radioactivity in the water layer, rinses, foam plugs and traps. Average total radiocarbon recoveries throughout the study ranged from 92.4% to 97.8% ([phenyl-U-14C] o,m-DBT), 94.3% to 102.7% ([phenyl-U-14C] o,o-DTPM), and 95.1% to 103.4% ([14C] tested impurity) for high-dose samples, and from 93.4% to 98.6% ([phenyl-U-14C] o,m-DBT), 91.3% to 104.8%  ([phenyl-U-14C] o,o-DTPM), and 95.1% to 98.6% ([14C] tested impurity) for low-dose samples. The production of CO2 between low dose and high dose samples in the [phenyl-U-14C] o,m-DBT, [phenyl-U-14C] o-o-DTPM, and [14C] tested impurity was comparable. 


DBT degraded moderately in all three labels under the conditions of the test and represented an average of 26.2% AR (high-dose) [phenyl-U-14C] o,m-DBT following 63 days of incubation, 15.5% AR (high-dose) [phenyl-U-14C] o,o-DTPM following 62 days of incubation, 9.9% AR (high-dose) [14C] tested impurity following 63 days of incubation.


Degradation products were present in the water layers with amended solids in the [phenyl-U-14C] o,m-DBT and [14C] tested impurity samples with the exception of [phenyl-U-14C] o,o-DTPM based on the HPLC data. Unknown degradates for [phenyl-U-14C] o,m-DBT at ~10.00 min and ~14.00 min represented a maximum average of 21.2% AR and 22.1% AR (high-dose) and for the [14C] tested impurity at ~14.40 min represented a maximum average of 27.9% AR (high-dose) both at T63d of the incubation period. Low dose aqueous samples with amended solids were not analyzed by HPLC due to the low radioactivity present in the samples.


The sterile control samples were sacrificed after 7, 30, and 63 days ([phenyl-U-14C] o,m-DBT), 7, 30, and 62 days ([phenyl-U-14C] o,o-DTPM), and 7, 29, and 63 days ([14C] tested impurity) of incubation. The average radiocarbon recoveries ranged from 98.9 to 106.0% AR ([phenyl-U-14C] o,m-DBT), 93.4 to 100.2% AR ([phenyl-U-14C] o,o-DTPM), and 99.6 to 103.7% AR ([14C] tested impurity). The HPLC analysis of the sterile samples showed minimal degradation of DBT. No unknown degradates were present across all three labels that represented more than 9.6% AR at ~ 13.97 in the [phenyl-U-14C] o,m-DBT (Sterile high-dose).


The DT50 and DT90 values for individual components of DBT (high-dose) were initially calculated using single first-order (SFO) model, with additional models first-order multi-compartment (FOMC), double first-order parallel (DFOP), and hockey stick (HS) used in order to obtain the best fit. Kinetic evaluations with CAKE software (version 3.3) following kinetic guidelines using FOCUS. The results of the kinetic evaluations are shown in the table below. The half-life was determined as 56.9 days ([phenyl-U-14C] o,m-DBT), >10,000 days ([phenyl-U-14C] o,o-DTPM), and 32.8 days ([14C] tested impurity) in the high dose samples.





































Test SubstanceDT50 (days)DT90 (days)Chi2 Err%R2kinetic Model

[phenyl-U-14C]o,m-DBT


56.91895.290.9037SFO

[phenyl-U-14C]o,o-DTPM


> 10,000> 10,0001.960.1285SFO

[14C] tested impurity


32.8109220.7205SFO

Description of key information

The registered substance contains concentration > 0.1 % of a PBT/ vPvB compound. According to the Echa Guidance R11 related to the PBT/vPvB assessment, in that case, the registered substance has to be considered also as a PBT/vPvB substance.
To answer the CCH-D-2114527842-47-01/F about the persistency datagap of the Benzyltoluene dossier, the studies performed on the relevant impurity (Dibenzyltoluene: CAS 53585-53-8) were added in section 5.2.2.


 


An aerobic mineralization preliminary and definitive study (OECD 309) was conducted with [14C]DBT Test Substances using aerobic natural water with amended solids. The tests were performed at 12°C. Two relevant compounds of DBT substance were radiolabelled : o,m-DBT, o,o-DTPM and one relevant impurity.


The half-life of DBT during the study was determined as 56.9 days ([phenyl-U-14C] o,m-DBT), >10,000 days ([phenyl-U-14C] o,o-DTPM), and 32.8 days (relevant [14C] impurity) (SFO model).


Degradation products were observed throughout the study in two out of the three labels. Unknown metabolites were detected in o,m-DBT and the relevant impurity and were tentatively analyzed by LC-MS/MS.


Based on this study, o,m-DBT can be considered as persistent and o,o-DTPM can be considered as persistent /very persistent.

Key value for chemical safety assessment

Half-life in freshwater:
56.9 d
at the temperature of:
12 °C

Additional information