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Environmental fate & pathways

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
Study period:
8 October 1999 to 17 November 1999
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 306 (Biodegradability in Seawater)
Deviations:
not specified
Principles of method if other than guideline:
Not applicable
GLP compliance:
yes (incl. certificate)
Radiolabelling:
no
Oxygen conditions:
not specified
Inoculum or test system:
natural water
Details on source and properties of surface water:
- Details on collection: seawater was collected from the Burham-on-Crouch estuary at high water. The Crouch estuary has no industrial and no river inputs.
- Storage conditions: dark, laboratory ambient temperature
- Storage length: up to six days
- Water filtered: yes
- Type and size of filter used, if any: suspended solids were removed from the raw seawater using a hydro-cyclone and settlement.
- All other template details: Not reported
Details on source and properties of sediment:
Not applicable
Details on inoculum:
Not applicable
Duration of test (contact time):
28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
other: ratio of biochemical oxygen demand to theoretical or chemical oxygen demand
Details on study design:
TEST CONDITIONS
- Test temperature: 20 +/- 1 degree C
- Continuous darkness: yes
- All other template details: Not reported

TEST SYSTEM
- Culturing apparatus: standard BOD bottles
- Number of culture flasks/concentration: not reported
- All other template details: Not reported

SAMPLING
- Sampling frequency: every 7 days
- Sampling method: dissolved oxygen meter

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Abiotic sterile control: no
- Toxicity control: not applicable
- Other: not applicable

STATISTICAL METHODS: not reported
Reference substance:
acetic acid, sodium salt
Remarks:
at 5 mg/L
Test performance:
Trisodium HEDTA dihydrate failed to meet the requirements for a pass in the test (>60% degradation relative to the ThOD value).
% Degr.:
< 0
Parameter:
O2 consumption
Sampling time:
28 d
Transformation products:
not specified
Details on transformation products:
Not reported
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): the incubator temperature recorded on day 14 was 21.4 degrees C, marginally above the 15 to 20 +/- 1 degree C range quoted in the protocol. This was not considered to be a significant deviation.
- All other template details: Not reported
Results with reference substance:
The percent degradation values for the reference substance was: day 7 = 75%, day 14 = 76%, day 21 = 79%, day 28 = 89%

Table 1. Calculated percent degradation values for test substance and reference material.

   Day 7  Day 14  Day 21  Day 28
 Test Substance  -8  -6  0  -8
 Reference material  75  76  79  89

Note: the theoretical oxygen demand (ThOD) of the reference material, sodium acetate, is 780 mg O2/L

Validity criteria fulfilled:
no
Remarks:
test material was not >60% degradation relative to the ThOD value, a maximum of 0% was recorded
Conclusions:
The substance is not necessarily not biodegradable under environmental conditions, but indicates more work would be necessary to establish biodegradability.
Executive summary:

Trisodium HEDTA dihydrate failed to meet the requirements for a pass in this test (>60% degradation relative to the ThOD value - a maximum of 0% was recorded). However, because of the stringency of the test, this does not necessarily mean that the test substance is not biodegradable under environmental conditions, but indicates that more work would be necessary to establish biodegradability.

The guideline requires that the reference material degrades by at least 60% of its ThOD, and that the blank dissolved oxygen loss should not exceed 30% of the initial oxygen concentration. Both of these criteria were satisfied for this test; a maximum value of 89% degradation of the sodium acetate was achieved, and the blank DO loss was 21.1%.

Endpoint:
biodegradation in water: sewage treatment simulation testing
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study
Justification for type of information:
The study with the read across substance is considered sufficient to fulfil the information requirements.
Reason / purpose:
read-across source
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 303 A (Simulation Test - Aerobic Sewage Treatment. A: Activated Sludge Units)
Principles of method if other than guideline:
The study was conducted according to the EEC Directive 79-831 Annex V, Part C: Methods for the Determination of Ecotoxicity, 5.2 Degradation - Biotic degradation: C.5 Activated Sludge Simulation Test, Bruessel, 1983 which corresponds to the OECD 303.
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Inoculation with activated sludge from a laboratory waste water plant, fed with domestic sevage. Regular removal of about 0.15 L/d of activated sludge to keep suspended solids at 2 g/L. Calculated sludge age about 20 d. Shock aeration in the separator for 30 sec every 2 h and discontinuous pumping of return sludge to improve settleability of the activated sludge. No observed loss of sludge in the effluent.
Duration of test (contact time):
93 d
Initial conc.:
10 mg/L
Based on:
DOC
Details on study design:
Modified OECD confirmatory plants (Husmann apparatus) were used.
Test and blank units were run in parallel (Uncoupled mode).
The volume of mixed liquor in the aeration basin equaled 3 L.

Feeding of OECD medium (synthetic sevage).
Continuous dosing of tap water: 0.5 L/h
Mean hydrolic retention time: 6 h
Separate and discontinuous dosing of concentrated synthetic sevage for 5 min every 2.4 h and stock solution of the test compound.
Mean DOC concentration of synthetic sevage: 106 mg/L

Mean volume load of the blank unit: 0.60 g DOC/Lxd
Mean sludge load of the blank unit: 0.23 g DOC/gSSxd
Compartment:
other: water / sediment, material (mass) balance
Remarks on result:
other: no data
Key result
% Degr.:
>= 0 - <= 10
Parameter:
DOC removal
Sampling time:
70 d
Transformation products:
not specified
Details on results:
Elimination in phase I (day 35-77) : 2 % DOC
Elimination in phase II (day 78-93) : 31 % DOC

Elimination in the blank unit 92 % DOC

The test compound was not eliminated up to a test duration of 77 days.
After that time an elimination took place, presumably by biodegradation.
Conclusions:
Under test conditions no biodegradation observed.
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
read-across based on grouping of substances (category approach)
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Justification for type of information:
The study with the read across substance is considered sufficient to fulfil the information requirements.
Reason / purpose:
read-across source
Principles of method if other than guideline:
No information on guideline.
GLP compliance:
no
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Key result
% Degr.:
ca. 3.2 - ca. 5.6
Parameter:
test mat. analysis
Sampling time:
4 wk
Key result
% Degr.:
ca. 9.1 - ca. 15.2
Parameter:
test mat. analysis
Sampling time:
10 wk
Key result
Compartment:
natural water: freshwater
DT50:
ca. 200 - ca. 300 d
Type:
not specified
Temp.:
20 °C
Transformation products:
no

The degradative abilities of aerobically incubated sediments were investigated by Tiedje (1975) and the results were similar to soil. The following rates of EDTA degradation per 4 weeks and total degradation after 10 weeks were found: Wintergreen lake, 3.6% and 11.3%, Clear Lake, 5.6% and 15.2%; and Mill Pond 3.2% and 9.1%. A half-life for aerobic sediment between 200 and 300 days related to mineralisation is assumed.

For the anaerobic degradation in sediment only a qualitative investigation indicates no degradation after 7 weeks (Tiedje, 1975; 1977). Therefore, no biodegradation for the anaerobic parts of the sediments is assumed.

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