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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water and sediment: simulation testing, other
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
comparable to guideline study with acceptable restrictions
Remarks:
Minor limitations in experimental design (i.e. smaller scale than recommended) and reporting (e.g. test item concentration, number of replicates, experimental conditions).
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 308 (Aerobic and Anaerobic Transformation in Aquatic Sediment Systems)
Version / remarks:
2002
Deviations:
yes
Remarks:
Test item loading was ten times less than recommended in the guidelines
GLP compliance:
not specified
Remarks:
Study is published in a peer-reviewed journal.
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source of test material: J&K Scientific (Shanghai, China)
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment: freshwater
Details on source and properties of surface water:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): Natural water samples were collected from four main urban aqueous systems in the city of Nanjing, China, namely Yangtze River, Qinhuai River, Xuanwu Lake, and Mochou Lake. At each sampling point, water samples were collected at three different depths from the surface to the bottom, and then mixed together.
- Storage conditions: Filtered and kept cool (4 °C) until their use.
- Storage length: 3 days
- pH at time of collection: Yangtze River 7.61; Qinhuai River 7.63; Xuanwu Lake 7.81; Mochou Lake 7.48
- Electrical conductivity: Yangtze River 409 dS/cm; Qinhuai River 574 dS/cm; Xuanwu Lake 415 dS/cm; Mochou Lake 477 dS/cm
- Redox potential (mv) initial/final: Yangtze River 397 mV; Qinhuai River 358 mV; Xuanwu Lake 401 mV; Mochou Lake 329 mV
- Oxygen concentration (mg/l) initial/final: Yangtze River 5.95 mg/L; Qinhuai River 6.72 mg/L; Xuanwu Lake 5.07 mg/L; Mochou Lake 4.76 mg/L
- Water filtered: yes
- Type and size of filter used, if any: 0.45-μm glass fiber filters
Details on source and properties of sediment:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): Natural sediment samples were collected from four main urban aqueous systems in the city of Nanjing, China, namely Yangtze River, Qinhuai River, Xuanwu Lake, and Mochou Lake. Sediments were taken from the surface layer (≤20 cm in depth) by a Van Veen grab sampler (25 ×40× 30 cm).
- Storage conditions: All sediments were freeze-dried, gently ground to pass through a sieve (2 mm), and then stored at 4 °C.
- Textural classification (%sand/silt/clay): Yangtze River 81.79/13.17/5.04; Qinhuai River 59.31/23.70/16.98; Xuanwu Lake 37.48/48.99/13.52; Mochou Lake 34.13/57.01/8.86
- pH at time of collection: Yangtze River 7.83; Qinhuai River 7.47; Xuanwu Lake 7.52; Mochou Lake 7.30
- Electrical conductivity: Yangtze River 589 dS/cm; Qinhuai River 592 dS/cm; Xuanwu Lake 570 dS/cm; Mochou Lake 561 dS/cm
- Organic carbon (%): Yangtze River 0.53%; Qinhuai River 1.10%; Xuanwu Lake 1.74%; Mochou Lake 2.61%
- CEC (meq/100 g): Yangtze River 13.06; Qinhuai River 14.98; Xuanwu Lake 22.45; Mochou Lake 26.56
- Redox potential (mv) initial/final: Not determined
- Sediment samples sieved: yes
Details on inoculum:
No additional inoculum was added. Microorganisms were naturally present in the sediment samples.
Duration of test (contact time):
80 d
Based on:
not specified
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: Five grams of freeze-dried sediment without autoclavation was weighed and added into 30-mL amber glass tubes to form a 2.5-cm sediment layer. The associated water samples were filtered (0.45 μm) and added simultaneously to achieve a water/sediment ratio of 3/1 (w/w).
- Solubilising agent (type and concentration if used): The test item pre-dissolved in methanol was spiked into the water phase, and the percentage of the methanol spiked was 25 μL, which is below 0.1 % (v/v) of the water used.
- Test temperature: 21 ± 2 °C
- pH: Not reported
- Continuous darkness: yes
- Any indication of the test material adsorbing to the walls of the test apparatus: Not reported
- Other: The systems were preconditioned for approximately 2 weeks at a constant temperature, and the dissolved oxygen, pH and redox potential of the water were measured regularly in the test systems during the preconditioning period.

TEST SYSTEM
- Culturing apparatus: 30 mL amber glass tubes
- Number of culture flasks/concentration: Not reported
- Method used to create aerobic conditions: Test vessels have a frit in the inlet tube to bubble air into the water phase to achieve aerobic conditions.
- Details of trap for CO2 and volatile organics if used: None reported

SAMPLING
- Sampling frequency: Two tubes were sacrificed at each sampling time (not reported) for test item treatments. The control group was analysed at the end of the experiment.
- Sampling method used per analysis type: Sediment and water were separated and each was analysed for the test item.
- Sterility check if applicable: No
- Sample storage before analysis: Samples were extracted, concentration and stored at −20 °C for further analysis.

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION
CONTROL AND BLANK SYSTEM
- Inoculum blank: Two tubes that were not spiked with the test item were set as the blank group.
- Abiotic sterile control: Two tubes with autoclaved deionised water but no sediment were set as the control group.
- Toxicity control: No toxicity control.

STATISTICAL METHODS: The DT values for the test item in both the aqueous phase and the whole system have been mostly calculated from fitted concentration decay formulae, but some of them (Xuanwu Lake and Mochou Lake) were determined on the basis of evaluating graphical data when the fit by formulae was significantly different from the graphic (R2< 0.85).
Compartment:
natural water: freshwater
DT50:
13.4 d
St. dev.:
1.4
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Yangtze River
Compartment:
natural water: freshwater
DT50:
4.1 d
St. dev.:
0.6
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Qinhuai River
Compartment:
natural water: freshwater
DT50:
7.1 d
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Xuanwu Lake
Remarks:
graphically determined value
Compartment:
natural water: freshwater
DT50:
6.5 d
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Mochou Lake
Remarks:
graphically determined value
Compartment:
entire system
DT50:
29 d
St. dev.:
1.7
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Yangtze River
Compartment:
entire system
DT50:
30.8 d
St. dev.:
1.5
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Qinhuai River
Compartment:
entire system
DT50:
28.8 d
St. dev.:
2.4
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Xuanwu Lake
Compartment:
entire system
DT50:
25.6 d
St. dev.:
1.8
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Mochou Lake
Key result
Compartment:
entire system
DT50:
28.55 d
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other: Mean of the four sampling sites
Other kinetic parameters:
first order rate constant
other: DT90
Transformation products:
not measured
Evaporation of parent compound:
not measured
Volatile metabolites:
not measured
Residues:
yes
Details on results:
In the whole system, the disappearance rate was lower than that observed in the water phase. All the experiments in this study were performed in the absence of light, which ensured that photolysis was not a possible cause for the dissipation of target compounds in the total system. In addition, the result of the control experiment showed that the loss of test item in autoclaved deionised water was negligible (<10 %) within 80 days, indicating that degradation mechanisms such as hydrolysis or oxidation-reduction reactions could be eliminated. Thus, it appears that biotransformation is the most plausible cause for the disappearance of the test item.

Table 1. k, DT50, and DT90 values with standard deviation of the test item for the water phase and whole system during the degradation experiment

 Sample  Water           Total (water and sediment)         
   k  R2  DT50  DT90  k  R2  DT50  DT90
 Yangtze River  0.033±0.004  0.8989  13.4±1.4  39.7±2.1  0.024±0.005  0.9862  29.0±1.7  96.1±7.2
 Qinhuai River  0.035±0.006  0.9427  4.1±0.6  54.6±3.8  0.023±0.007  0.9837  30.8±1.5  100.8±8.6
 Xuanwu Lake  0.054±0.009  0.7965  7.1*  16.4*  0.025±0.003  0.9882  28.8±2.4  93.2±5.6
 Mochou Lake  0.052±0.006  0.8076  6.5*  18.4*  0.024±0.004  0.9329  25.6±1.8  92.6±7.3

* graphically determined value

Validity criteria fulfilled:
yes
Remarks:
Analytical sensitivities and recoveries were adequate. DT50 and DT90 values and confidence limits were calculated from fitted concentration decay formulae or determined graphically.
Conclusions:
The DT50 values were determined to be 13.4 ± 1.4, 4.1 ± 0.6, 7.1 and 6.5 days for water from the Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, respectively, and the DT50 values for the whole system (water + sediment) were 29.0 ± 1.7, 30.8 ± 1.5, 28.8 ± 2.4 and 25.6 ± 1.8 days, respectively.
Executive summary:

The combined sorption and degradation of the test material in a natural water-sediment system was determined according to OECD Guideline 308 under aerobic conditions. Water and sediment were collected from Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, in China. The experiments were conducted in 30-mL amber glass tubes, containing 5 grams (dry weight) of sediment (2.5 cm sediment layer) and overlying water to achieve a water/sediment ratio of 3/1 (w/w). The study included an abiotic control and an inoculum control. The combined sorption and degradation tests were conducted in duplicate for 80 days. Sediment and water samples were analysed by UPLC with MS-ESI and concentrations were corrected based on the recovery data. The DT50 values were determined to be 13.4 ± 1.4, 4.1 ± 0.6, 7.1 and 6.5 days for water from the Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, respectively, and the DT50 values for the whole system (water + sediment) were 29.0 ± 1.7, 30.8 ± 1.5, 28.8 ± 2.4 and 25.6 ± 1.8 days, respectively. In the whole system, the disappearance rate was lower than that observed in the water phase. All the experiments in this study were performed in the absence of light, which ensured that photolysis was not a possible cause for the dissipation of target compounds in the total system. In addition, the result of the control experiment showed that the loss of test item in autoclaved deionised water was negligible (<10 %) within 80 days, indicating that degradation mechanisms such as hydrolysis or oxidation-reduction reactions could be eliminated. Thus, it appears that biotransformation is the most plausible cause for the disappearance of the test item. This study is reliable with restrictions (Klimisch 2) as it was conducted according to guideline, however there were minor limitations in experimental design (i.e. smaller scale than recommended) and reporting (e.g. test item concentration, number of replicates, experimental conditions).

Description of key information

The DT50 values were determined to be 13.4 ± 1.4, 4.1 ± 0.6, 7.1 and 6.5 days for water from the Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, respectively, and the DT50 values for the whole system (water + sediment) were 29.0 ± 1.7, 30.8 ± 1.5, 28.8 ± 2.4 and 25.6 ± 1.8 days, respectively. The average of the four DT50 values (28.55 d) in the entire water-sediment system is reported as the key value for chemical safety assessment.

Key value for chemical safety assessment

Half-life in freshwater sediment:
28.55 d
at the temperature of:
21 °C

Additional information

The combined sorption and degradation of the test material in a natural water-sediment system was determined according to OECD Guideline 308 under aerobic conditions. Water and sediment were collected from Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, in China. The experiments were conducted in 30-mL amber glass tubes, containing 5 grams (dry weight) of sediment (2.5 cm sediment layer) and overlying water to achieve a water/sediment ratio of 3/1 (w/w). The study included an abiotic control and an inoculum control. The combined sorption and degradation tests were conducted in duplicate for 80 days. Sediment and water samples were analysed by UPLC with MS-ESI and concentrations were corrected based on the recovery data. The DT50 values were determined to be 13.4 ± 1.4, 4.1 ± 0.6, 7.1 and 6.5 days for water from the Yangtze River, Qinhuai River, Xuanwu Lake and Mochou Lake, respectively, and the DT50 values for the whole system (water + sediment) were 29.0 ± 1.7, 30.8 ± 1.5, 28.8 ± 2.4 and 25.6 ± 1.8 days, respectively. In the whole system, the disappearance rate was lower than that observed in the water phase. All the experiments in this study were performed in the absence of light, which ensured that photolysis was not a possible cause for the dissipation of target compounds in the total system. In addition, the result of the control experiment showed that the loss of test item in autoclaved deionised water was negligible (<10 %) within 80 days, indicating that degradation mechanisms such as hydrolysis or oxidation-reduction reactions could be eliminated. Thus, it appears that biotransformation is the most plausible cause for the disappearance of the test item. This study is reliable with restrictions (Klimisch 2) as it was conducted according to guideline, however there were minor limitations in experimental design (i.e. smaller scale than recommended) and reporting (e.g. test item concentration, number of replicates, experimental conditions).

In a supporting study. the degradation of 3-(4-methylbenzylidene) camphor under various redox conditions was tested using water and sediment collected from a groundwater aquifer in South Australia. Samples containing 5 g of aquifer materials (97.1% sand / 0.8% silt / 1.7% clay, 0.4% organic carbon) and 5 mL of groundwater, amended with 1 μg test item/g sediment, were prepared under aerobic, anaerobic-nitrate reducing, sulfate reducing and Fe(III) reducing conditions and degradation was monitored over 77 days. Triplicate samples were prepared for each treatment, alongside sterile controls. Samples were incubated at 20 °C under continuous darkness, and test item concentrations were analysed on Days 0, 7, 14, 21, 28, 35, 49, 63, and 77 using GC-MS. Under aerobic conditions the DT50 was 33 day, showing that the test item is not persistent under aerobic conditions in aquifers.

Degradation half-lives of the test item under different redox conditions had the following order: aerobic (33 d) > anaerobic control (75 d) > Fe(III) reducing (77 d) > nitrate reducing (80 d) > sulfate reducing (85 d). No hydrolysis of the test item was observed in the sterile control. This study is reliable with restrictions (Klimisch 2) as it was not conducted according to guideline, however the study design is scientifically acceptable, with minor limitations in experimental design (e.g. small test volume, mixture conditions).