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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
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)
GLP compliance:
yes (incl. QA statement)
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source (i.e. manufacturer or supplier) and lot/batch number of test material:
Hangzhou Grascent Co., Ltd.
BS18B03221
- Purity, including information on contaminants, isomers, etc.:
~80%

STABILITY AND STORAGE CONDITIONS OF TEST MATERIAL
- Storage condition of test material:
-20℃
- Stability and homogeneity of the test material in the vehicle/solvent under test conditions (e.g. in the exposure medium) and during storage:
Stable
- Stability in the medium, i.e. sensitivity of the test material to hydrolysis and/or photolysis:
Stable
- Solubility and stability of the test material in the solvent/vehicle and the exposure medium:
6mg/L @23℃
Radiolabelling:
yes
Remarks:
14C-labeled
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Details on source and properties of surface water:
- Details on collection (e.g. location, sampling depth, contamination history, procedure):
Origin: Great Ouse River, Huntingdon, Cambridgeshire, UK (52º19’ - 0º10’)
Date of sampling: 31 March 2020
Sampling depth: 187cm

- Storage conditions:
at 2 - 8°C with aeration
- Storage length:
- Temperature (°C) at time of collection:
7.6℃
- pH at time of collection:
9.31
- Biomass:
3.75 * 10E4 unit/g
- Oxygen concentration (mg/l) initial/final:
105.0
- Hardness (CaCO3):
370mg/L
- Dissolved organic carbon (%):
6.6mg/L
- Water filtered:
yes
- Type and size of filter used, if any:
nylon filter of mesh size ca 100 μm.
Duration of test (contact time):
61 d
Initial conc.:
10 µg/L
Based on:
test mat.
Initial conc.:
100 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Details on study design:
Preparation and Incubation of the Test System
Portions of filtered surface water (100 mL) were added to cylindrical 500 mL glass bottles.
For each concentration of methyl cedryl ketone, the following vessels were established:
Symbol Details Total vessels
- Preliminary experiment 1 (high concentration only) 3
- Preliminary experiment 2 (high concentration only) 3
FT Duplicate flasks at 7 sampling times plus two spare flasks 16
FS Duplicate sterile controls at 61 days, sterilized by autoclaving 2
(121ºC, 15 minutes), prior to addition of methyl cedryl ketone.

The following additional vessels were prepared:
Symbol Details Total vessels
FC Reference control containing [14C]-benzoic acid at 2
10 μg/L (to confirm minimum microbial activity)
FSolvent Reference control containing [14C]-benzoic acid at 2
10 μg/L and solvent used for the test item application
(to determine possible adverse effects of solvent)
In addition, five vessels of surface water were set up for microbiological analysis and two vessels were set up for measurements of pH and oxygen content. These vessels were not treated with methyl cedryl ketone.
Samples established for treatment with the methyl cedryl ketone and reference control [14C]-benzoic acid were incorporated into individual flow-through systems.

SAMPLING
- Sampling frequency in main experiment:
For each concentration of methyl cedryl ketone, duplicate samples of surface water were taken for analysis immediately after application and after 2, 7, 14, 30, 44 and 61 days of incubation. Duplicate sterile controls were taken for analysis after 61 days of incubation.
Trapping media were taken for analysis with the associated samples at sampling.
Reference substance:
other: [ring-14C]-Benzoic acid
Compartment:
natural water: freshwater
% Recovery:
82.1
Remarks on result:
other: Recoveries of Radioactivity from Incubated Surface Water Treated with [14C]-Methyl Cedryl Ketone (Nominal 10 μg/L)
Compartment:
natural water: freshwater
% Recovery:
74.4
Remarks on result:
other: Recoveries of Radioactivity from Incubated Surface Water Treated with [14C]-Methyl Cedryl Ketone (Nominal 100 μg/L)
Key result
Compartment:
natural water: freshwater
DT50:
34.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: at a concentration of 10 μg/L
Key result
Compartment:
natural water: freshwater
DT50:
39.3 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: at a concentration of 100 μg/L
Mineralization rate (in CO2):
0.7 other: Low levels of mineralization were observed, accounting for a maximum of 0.7% AR as carbon dioxide.
Transformation products:
yes
No.:
#1
No.:
#2
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes

For the low concentration water, the total recoveries declined from 98.4 – 98.6% applied radioactivity (AR) at time zero to 80.4 – 83.8% AR by Day 61. The level of radioactivity in the water/solvent mixture declined from 97.8 – 97.9% AR at time zero to 54.8–55.8% AR by Day 61. Low levels (<1.5% AR) of radioactivity were recovered from the test vessel rinses up to Day 61. The test vessel adapter heads rinsed with methanol recovered significant levels of radioactivity, reaching a maximum of 31.5% AR at Day 44 then declining to 19.0-24.4% AR by Day 61. Low levels of radioactivity were extracted from the plastic tubing between the test vessel and the first trapping vessel at Day 61 (2.1–4.9% AR). No significant radioactivity (<0.7% AR) was recovered from the trapping solutions.

For the high concentration water, the total recoveries declined from 97.0 - 100.0% AR at time zero to 73.0 – 75.8% AR by Day 61. The level of radioactivity in the water/solvent mixture declined from 96.5 - 99.5% AR at time zero to 51.5 – 57.6% AR by Day 61. Low levels (<1.1% AR) of radioactivity were recovered from the test vessel rinses up to Day 61.
Significant levels of radioactivity were recovered from the adapter head rinses, reaching a maximum of 24.2% AR at Day 44 then declining to 11.4 - 14.1% AR by Day 61. Low levels of radioactivity were extracted from the plastic tubing between the test vessel and the first trapping vessel at Day 61 (5.3 – 6.2% AR). No significant radioactivity (<0.4% AR) was recovered from the trapping solutions.

For the low concentration sterile waters at Day 61, the total recoveries were 77.8 – 85.2% AR. The level of radioactivity in the water/acetonitrile mixture was 46.5–54.3% AR. No significant radioactivity (<0.8% AR) was recovered in the test vessel methanol rinse. The test vessel adapter heads rinsed with methanol recovered significant levels of radioactivity (21.5 - 37.9% AR). No significant radioactivity (<1.5% AR) was recovered from the extraction of the plastic tubing between the test vessel and the first trapping vessel. No radioactivity was detected in the trapping media.

For the high concentration sterile waters at Day 61, the total recoveries were 91.7 – 95.5% AR. The level of radioactivity in the water/acetonitrile mixture was 65.1–67.2% AR. No significant radioactivity (<1.2% AR) was recovered from the test vessel methanol rinses. The test vessel adapter heads rinsed with methanol recovered significant levels of radioactivity (17.2 – 29.2% AR). The extraction of the plastic tubing between the FSH-1 test vessel and its first trapping vessel recovered 6.5% AR. No radioactivity was detected in the trapping media.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study:
Only a small amount of mineralization was observed, accounting for a maximum of 0.7% AR as carbon dioxide.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study:
Volatile radioactivity, confirmed as methyl cedryl ketone, adhered to the test vessel adapter heads and to the plastic tubing of the trap lines between the test vessel and the first trapping vessel.

STERILE TREATMENTS (if used)
- Transformation of the parent compound: no
Results with reference substance:
Recoveries of Radioactivity from Incubated Surface Water Treated with Reference Control [14C]-Benzoic Acid (10 mg/L)
FC samples:
Time after application (days) Sample identity Surface water Volatiles Total recovery
14 FC-1 22.6 71.7 94.3
FC-2 26.7 67.2 93.9
FSolvent samples:
Time after application (days) Sample identity Surface water Volatiles Total recovery
14 FSolvent-1 26.7 62.2 88.9
FSolvent-2 21.0 61.0 82.0
Results expressed as % applied radioactivity
Validity criteria fulfilled:
yes
Conclusions:
Natural surface water was treated with [14C]-methyl cedryl ketone at nominal application rates of 10 μg/L and 100 μg/L. Treated surface water samples were kept in test vessels sealed with 2-way taps and incubated with continuous stirring to maintain aerobic conditions at 12 ± 2℃ in darkness for periods of up to 61 days.

DT50 and DT90 values for the decline of methyl cedryl ketone from the surface water are shown below.
Compartment Nominal 10 μg/L Nominal 100 μg/L
DT50 (days) DT90 (days) DT50 (days) DT90 (days)
Water 34.4 233 39.3 130

Methyl cedryl ketone in surface water treated at 10 μg/L and 100 μg/L degraded to two major unknown degradation products; unknown B with retention time of 19.7 minutes (up to 15.4% AR; tentatively identified as a di-oxygenated and hydrated form of methyl cedryl ketone with a molecular formula of C17H28O3) and unknown C with retention time of 21.3 minutes (up to 12.9% AR; tentatively identified as a di-oxygenated form of methyl cedryl ketone with a molecular formula of C17H26O3).
Low levels of mineralization were observed, accounting for a maximum of 0.7% AR as carbon dioxide. Volatile radioactivity, confirmed as methyl cedryl ketone, adhered to the test vessel adapter heads and to the plastic tubing of the trap lines between the test vessel and the first trapping vessel.

Description of key information

Natural surface water was treated with [14C]-methyl cedryl ketone at nominal application rates of 10 μg/L and 100 μg/L. Treated surface water samples were kept in test vessels sealed with 2-way taps and incubated with continuous stirring to maintain aerobic conditions at 12 ± 2℃ in darkness for periods of up to 61 days.

DT50 and DT90 values for the decline of methyl cedryl ketone from the surface water are shown below.

Compartment                                            Nominal 10 μg/L                                      Nominal 100 μg/L

                                                           DT50 (days)      DT90 (days)                 DT50 (days)      DT90 (days)

Water                                                    34.4                    233                               39.3                    130

Methyl cedryl ketone in surface water treated at 10 μg/L and 100 μg/L degraded to two major unknown degradation products; unknown B with retention time of 19.7 minutes (up to 15.4% AR; tentatively identified as a di-oxygenated and hydrated form of methyl cedryl ketone with a molecular formula of C17H28O3) and unknown C with retention time of 21.3 minutes (up to 12.9% AR; tentatively identified as a di-oxygenated form of methyl cedryl ketone with a molecular formula of C17H26O3).

Low levels of mineralization were observed, accounting for a maximum of 0.7% AR as carbon dioxide. Volatile radioactivity, confirmed as methyl cedryl ketone, adhered to the test vessel adapter heads and to the plastic tubing of the trap lines between the test vessel and the first trapping vessel.

Key value for chemical safety assessment

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

Additional information