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Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
Data is from experimental study report
Qualifier:
according to guideline
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Version / remarks:
stock solution prepared in water by passive dosing (no solvent).
GLP compliance:
no
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
natural water
Remarks:
Stream of good ecological quality and without known point sources close to sampling point
Details on source and properties of surface water:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): Natural water sampled from Gudenåen (DK) 15th of June 2020. WGS84: 56°6'23.2"N 9°43'17.4"E
- Other details of sample (eg: colour and turbidity): The water was quite clear with a slight light brown hint. Total suspended solids was 2.0 mg/L, total dissolved solids was 210 mg/L.
- Sampling depth: 5-20 cm below surface. No pre-treatment of the natural water.
- Storage conditions: Water kept at 20 ± 1,5°C during transport to lab (4 hours), then stored at 12°C until test setup within 30 hours of sampling.
- Storage length: 30 hrs
- Temperature (°C) at time of collection: 20.0°C.
- pH at time of collection: 6.5
- Biomass (e.g. in mg microbial C/100 mg, CFU or other):
Plate count (24 hours incubation): 36 CFU/mL
Plate count (72 hours incubation): 1300 CFU/mL
- Water filtered: no
- Other: Dissolved non-volatile organic carbon (NVOC) was measured instead of DOC/TOC and was 4.4 mg/L.
Duration of test (contact time):
> 2 - < 30 d
Initial conc.:
0.3 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 14.5 mL surface water used in each test system, spiked with 0.5 mL stock solution prepared in water by passive dosing.
- Composition of medium: Natural water used as medium
- Test temperature: 12°C
- pH: 6.5
- pH adjusted: no
- Aeration of dilution water: No aeration during test
- Suspended solids concentration: 2.0 mg/l
- Continuous darkness: yes
- Other: Conductivity: 334 µS/cm
- Non volatile dissolved organic carbon in natural water: 4.4 mg/L

TEST SYSTEM
- Culturing apparatus: 20 mL amber headspace vials
- Number of replicates: 15-18 replicate biotic and 15-18 replicate abiotic test systems were used.
- Method used to create aerobic conditions: Aerobic conditions created by using aerobic natural water (initial oxygen content 9.0 mg/L at 20 °C) and incubating using a headspace of 5 mL with a low test substance concentration of 0.3 mg/l.
- Test performed in closed vessels due to significant volatility of test substance: yes, test performed in closed vials.

SAMPLING
- Sampling frequency: At five time-points, three biotic and three abiotic test systems were sacrificed for analysis (day 2, 6, 14, 21, 27 and 30).
- Sampling method used per analysis type: Tests systems were put directly on the autosampler of the GCMS without storage.

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION
CONTROL AND BLANK SYSTEM
Blank test systems were prepared and incubated with biotic and abiotic test systsems and analyzed at each time-point (signal well below the 3% dilution of initial test concentration).
Carryover was < 1.0% and since test systems were analyzed alternating biotic and abiotic test systems this constitutes the detection limit in this test.

STATISTICAL METHODS: Triplicate ratios of biotic/abiotic test system peak areas were calculated for each time point and used in Graph-pad Prism 8.4.3 to fit the first order degradation model with lag phase: Y=IF(x0, Y0=1, K>0
Key result
% Degr.:
89
Parameter:
test mat. analysis
Sampling time:
30 d
Remarks on result:
other: primary degradation
Key result
Compartment:
natural water
DT50:
26 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other: Tlag =24 days
Other kinetic parameters:
first order rate constant
Transformation products:
not measured
Evaporation of parent compound:
no
Volatile metabolites:
not specified
Residues:
not specified
Validity criteria fulfilled:
not specified
Conclusions:
Primary biodegradation in surface water from a Danish stream was determined by compound specified analysis and was performed following the modified OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test). The DT50 of the test chemical was evaluated to be 26 days at 12°C. Primary percentage degradation of the test chemical was determined to be 89% at 30 days. Hence, test chemical was considered to be not persistent in surface water.
Executive summary:

Primary biodegradation in surface water from a Danish stream was determined by compound specified analysis. The study was performed following the modified OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test) under aerobic conditions. Natural water (stream of good ecological quality and without known point sources close to sampling point) sampled from Gudenåen (DK) 16th of June 2020. WGS84: 56°6'23.2"N 9°43'17.4"E at a dept of 5 -20 cm below surface was used as a surface water. The water was quite clear with a slight light brown hint. Total suspended solids was 2.0 mg/L, total dissolved solids was 210 mg/L. No pre-treatment was done of the natural water. Water kept at 20 ± 1.5°C during transport to lab (4 hours), then stored at 12°C until test setup within 30 hours of sampling. The temperature and pH at the time of collection of the sample was 20.0°C and 6.5 pH. Biomass i.e., plate count at 24 and 72 hr was 36 CFU/ml and 1281 CFU/ml, respectively. Water was not filtered. Dissolved non-volatile organic carbon (NVOC) was measured instead of DOC/TOC and was 4.4 mg/L. Study was performed using 20 mL amber headspace closed vials. A large no. of biotic test systems (15 -18 replicates) consisting of 14.5 ml surface water and 0.5 ml stock solution was prepared test vials. Stock solution was prepared in water by equilibrium partioning from a pre-loaded silicone rod (passive dosing). This method for preparing stock solutions avoids the need for solvents for spiking. A similar number of abiotic control test systems were prepared using 14.5 ml MilliQ water and 0.5 ml stock solution. Blanks were prepared with 15 ml MilliQ water. Aerobic conditions created by using aerobic natural water (initial oxygen content 9.0 mg/L at 20 °C)  and incubating using a headspace of 5 mL with a low test substance concentration of 0.3 mg/l. Test was conducted at a temperature of 12°C and pH of 6.5 under continuous darkness with conductivity of 334 µS/cm while rolling. pH of the test medium (natural water) was not adjusted. No aeration was provided during the study. Suspended solid concentrations uded in the study was 2.0 mg/l. At 5 -6 time-points, 3 biotic and 3 abiotic test systems were sacrificed for analysis (day2, 6, 14, 21, 27 and 30). Tests systems were put directly on the autosampler of the GCMS without storage. Blank test systems were prepared and incubated with biotic and abiotic test systems and analyzed at each time-point (signal well below the 3% dilution of initial test concentration). Analysis was carried out using direct immersion solid phase microextraction coupled to GC-MS. Carryover was < 1.0% and since test systems were analyzed alternating biotic and abiotic test systems this constitutes the detection limit in this test. Biodegradation was then evaluated by the ratio between peak areas in the biotic and abiotic test systems. Triplicate ratios of biotic/abiotic test system peak areas were calculated for each time point and used in Graph-pad Prism 8.4.3 to fit the first order degradation model with lag phase. The DT50 of the test chemical was evaluated to be 26 days at 12°C. Primary percentage degradation of the test chemical was determined to be 89% at 30 days. Thus, on the basis of results, test chemical was considered to be not persistent in surface water.

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
calculation (if not (Q)SAR)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
accepted calculation method
Justification for type of information:
Data is from computational model developed by USEPA
Qualifier:
according to guideline
Guideline:
other: Modeling database
Principles of method if other than guideline:
Fugacity Model by EPI Suite estimation database
GLP compliance:
no
Radiolabelling:
no
Oxygen conditions:
other: estimation
Inoculum or test system:
not specified
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
Level III Fugacity model
EPI Suite contains a Level III fugacity model. In general, fugacity models predict the partitioning of an organic compound in an evaluative environment. A Level III model assumes steady-state but not equilibrium conditions. The Level III model in EPI Suite predicts partitioning between air, soil, sediment and water using a combination of default parameters and various input parameters that may be user defined or estimated by other programs within EPI Suite.

The model environment consists of 4 main compartments: air, water sediment and soil. There are also sub-compartments such as an aerosol phase, suspended solids, and biota phase, within specific main compartments. A fixed temperature of 25ᵒC is assumed. Mass transport between the compartments via volatilization, diffusion, deposition and runoff are modeled. level III models is a steady state, non-equilibrium model. Steady state conditions mean that the change in concentration of a chemical in each compartment (i) with respect to time eventually approaches zero. The model does not assume that a common equilibrium (fugacity) exists between the phases, so if a chemical is emitted into one compartment it can partition to the other compartments. Loss of chemical occurs through two processes: reaction and advection. Reaction is the biotic or abiotic degradation of the chemical that is calculated using the user specified or model calculated half-lives of the chemical in each of the 4 main compartments. Advection processes are considered for the air, water and sediment compartments. Advection is the removal of chemical from a compartment through losses other than degradation (reaction). The rate of advection in a given compartment is determined by a flow rate (m3/hour), calculated by dividing the volume of the compartment by an advection time.
Compartment:
sediment
% Recovery:
0.673
Remarks on result:
other: Other details not known
Key result
% Degr.:
50
Parameter:
other: Half-life in sediment
Sampling time:
135 d
Remarks on result:
other: Other details not known
Key result
Compartment:
sediment
DT50:
135 d
Type:
other: estimated data
Temp.:
25 °C
Remarks on result:
other: Other details not known
Transformation products:
not specified
Evaporation of parent compound:
not specified
Volatile metabolites:
not specified
Residues:
not specified

Mass Amount

(percent)

Half-Life (hr)

Emissions (kg/hr)

Sediment

0.673

3.24e+003

0

 

Fugacity (atm)

Reaction (kg/hr)

Advection (kg/hr)

Reaction (percent)

Advection (percent)

Sediment

1.58e-009

1.76

0.164

0.0585

0.00547

Validity criteria fulfilled:
not specified
Conclusions:
Estimated half life of test chemical in sediment estimated to be 135 days (3240 h).
Executive summary:

Estimation Programs Interface (2017) prediction model was run to predict the half-life in sediment for the test chemical. The half-life period of test chemical in sediment is estimated to be 135 days (3240 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.673%), indicates that test chemical is not persistent in sediment.

Description of key information

Primary biodegradation in surface water from a Danish stream was determined by compound specified analysis. The study was performed following the modified OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test) under aerobic conditions. Natural water (stream of good ecological quality and without known point sources close to sampling point) sampled from Gudenåen (DK) 16th of June 2020. WGS84: 56°6'23.2"N 9°43'17.4"E at a dept of 5 -20 cm below surface was used as a surface water. The water was quite clear with a slight light brown hint. Total suspended solids was 2.0 mg/L, total dissolved solids was 210 mg/L. No pre-treatment was done of the natural water. Water kept at 20 ± 1.5°C during transport to lab (4 hours), then stored at 12°C until test setup within 30 hours of sampling. The temperature and pH at the time of collection of the sample was 20.0°C and 6.5 pH. Biomass i.e., plate count at 24 and 72 hr was 36 CFU/ml and 1281 CFU/ml, respectively. Water was not filtered. Dissolved non-volatile organic carbon (NVOC) was measured instead of DOC/TOC and was 4.4 mg/L. Study was performed using 20 mL amber headspace closed vials. A large no. of biotic test systems (15 -18 replicates) consisting of 14.5 ml surface water and 0.5 ml stock solution was prepared test vials. Stock solution was prepared in water by equilibrium partioning from a pre-loaded silicone rod (passive dosing). This method for preparing stock solutions avoids the need for solvents for spiking. A similar number of abiotic control test systems were prepared using 14.5 ml MilliQ water and 0.5 ml stock solution. Blanks were prepared with 15 ml MilliQ water. Aerobic conditions created by using aerobic natural water (initial oxygen content 9.0 mg/L at 20 °C)  and incubating using a headspace of 5 mL with a low test substance concentration of 0.3 mg/l. Test was conducted at a temperature of 12°C and pH of 6.5 under continuous darkness with conductivity of 334 µS/cm while rolling. pH of the test medium (natural water) was not adjusted. No aeration was provided during the study. Suspended solid concentrations uded in the study was 2.0 mg/l. At 5 -6 time-points, 3 biotic and 3 abiotic test systems were sacrificed for analysis (day2, 6, 14, 21, 27 and 30). Tests systems were put directly on the autosampler of the GCMS without storage. Blank test systems were prepared and incubated with biotic and abiotic test systems and analyzed at each time-point (signal well below the 3% dilution of initial test concentration). Analysis was carried out using direct immersion solid phase microextraction coupled to GC-MS. Carryover was < 1.0% and since test systems were analyzed alternating biotic and abiotic test systems this constitutes the detection limit in this test. Biodegradation was then evaluated by the ratio between peak areas in the biotic and abiotic test systems. Triplicate ratios of biotic/abiotic test system peak areas were calculated for each time point and used in Graph-pad Prism 8.4.3 to fit the first order degradation model with lag phase. The DT50 of the test chemical was evaluated to be 26 days at 12°C. Primary percentage degradation of the test chemical was determined to be 89% at 30 days. Thus, on the basis of results, test chemical was considered to be not persistent in surface water.

Key value for chemical safety assessment

Half-life in freshwater:
26 d
at the temperature of:
12 °C
Half-life in freshwater sediment:
135 d
at the temperature of:
25 °C

Additional information

Studies of biodegradation were evaluated for determing the persistence of test chemical. The studies are reported below:

In an experimental study, primary biodegradation in surface water from a Danish stream was determined by compound specified analysis. The study was performed following the modified OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test) under aerobic conditions. Natural water (stream of good ecological quality and without known point sources close to sampling point) sampled from Gudenåen (DK) 16th of June 2020. WGS84: 56°6'23.2"N 9°43'17.4"E at a dept of 5 -20 cm below surface was used as a surface water. The water was quite clear with a slight light brown hint. Total suspended solids was 2.0 mg/L, total dissolved solids was 210 mg/L. No pre-treatment was done of the natural water. Water kept at 20 ± 1.5°C during transport to lab (4 hours), then stored at 12°C until test setup within 30 hours of sampling. The temperature and pH at the time of collection of the sample was 20.0°C and 6.5 pH. Biomass i.e., plate count at 24 and 72 hr was 36 CFU/ml and 1281 CFU/ml, respectively. Water was not filtered. Dissolved non-volatile organic carbon (NVOC) was measured instead of DOC/TOC and was 4.4 mg/L. Study was performed using 20 mL amber headspace closed vials. A large no. of biotic test systems (15 -18 replicates) consisting of 14.5 ml surface water and 0.5 ml stock solution was prepared test vials. Stock solution was prepared in water by equilibrium partioning from a pre-loaded silicone rod (passive dosing). This method for preparing stock solutions avoids the need for solvents for spiking. A similar number of abiotic control test systems were prepared using 14.5 ml MilliQ water and 0.5 ml stock solution. Blanks were prepared with 15 ml MilliQ water. Aerobic conditions created by using aerobic natural water (initial oxygen content 9.0 mg/L at 20 °C)  and incubating using a headspace of 5 mL with a low test substance concentration of 0.3 mg/l. Test was conducted at a temperature of 12°C and pH of 6.5 under continuous darkness with conductivity of 334 µS/cm while rolling. pH of the test medium (natural water) was not adjusted. No aeration was provided during the study. Suspended solid concentrations uded in the study was 2.0 mg/l. At 5 -6 time-points, 3 biotic and 3 abiotic test systems were sacrificed for analysis (day2, 6, 14, 21, 27 and 30). Tests systems were put directly on the autosampler of the GCMS without storage. Blank test systems were prepared and incubated with biotic and abiotic test systems and analyzed at each time-point (signal well below the 3% dilution of initial test concentration). Analysis was carried out using direct immersion solid phase microextraction coupled to GC-MS. Carryover was < 1.0% and since test systems were analyzed alternating biotic and abiotic test systems this constitutes the detection limit in this test. Biodegradation was then evaluated by the ratio between peak areas in the biotic and abiotic test systems. Triplicate ratios of biotic/abiotic test system peak areas were calculated for each time point and used in Graph-pad Prism 8.4.3 to fit the first order degradation model with lag phase. The DT50 of the test chemical was evaluated to be 26 days at 12°C. Primary percentage degradation of the test chemical was determined to be 89% at 30 days. Thus, on the basis of results, test chemical was considered to be not persistent in surface water.

For the test chemical, Estimation Programs Interface (2017) prediction model was run to predict the half-life in sediment for the test chemical. The half-life period of test chemical in sediment is estimated to be 135 days (3240 hrs). However, as the percentage release of test chemical into the sediment is less than 1% (i.e, reported as 0.673%), indicates that test chemical is not persistent in sediment.

Thus, test chemical was considered to be not persistent.