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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
11 April 2003 to 09 May 2003
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
ISO 14593:1999 (Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium - Method by analysis of inorganic carbon in sealed vessels (CO2 headspace test))
Deviations:
yes
Remarks:
temperature readings not taken on two days; no adverse effect on study
Qualifier:
according to
Guideline:
EPA OPPTS 835.3120 (Sealed Vessel Carbon Dioxide Production Test)
Deviations:
yes
Remarks:
temperature readings not taken on two days; no adverse effect on study
Qualifier:
according to
Guideline:
other: ASTM E 1720-95 Sealed Vessel
Deviations:
yes
Remarks:
temperature readings not taken on two days; no adverse effect on study
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: sewage, predominiently domestic
Details on inoculum:
ACTIVATED SLUDGE
- Activated sludge was obtained from the aeration basin of the Wareham Wastewater Treatment Plant, Wareham, Massachusetts and the New Bedford Wastewater Treatment Plant, New Bedford, Masachusetts.
- Both facilities received primarily domestic waste.
- Activated sludge was collected on 11 April 2003 and transported to the testing facility.
- Upon arrival, sludge was poured through a 2 mm sieve and then centrifuged at 1500 rpm for 10 minutes. The supernatant was decanted and discarded.
- Concentrated solids were then combined in one sterile beaker and moisture content was determined to be 93.76 % using an automated moisture analyser.
- An inoculum stock solution containing 10 mg suspended solids/L was produced by adding sludge (0.0615 g) to mineral media (400 mL).
- The inoculum solution was prepared on the day of initiation of the acclimation phase and was continuously stirred until used.
- The microbial population of the inoculum was typically in the range 10E04 to 10E06 colony forming units (cfu) when added to the test vessels.
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
TOC
Details on study design:
TEST SYSTEM
- The test system consisted of individual 20 mL glass serum bottles.
- Prior to test initiation, the test vessels were rinsed with purified reagent water.
- Test vessels were identified with the project number, date and treatment type.
- To minimise bias, replicates were prepared, placed in the incubation chamber and sampled randomly.
- The test system was housed in the dark, in a walk-in environmental chamber controlled to maintain a temperature of 22 ± 2 °C.

TEST INITIATION
- Test solutions were prepared in 400 mL volumes of mineral salts medium (see Table 1, attached) by adding activated sludge solids (4 mg dry weight), soil extract (0.5 mL) and the appropriate volume of test or reference substance to yield 10 mgC/L.
- Blank control medium received only activated sludge and soil extract.
- Serum vials (24) were prepared for the test substance, reference substance and blank control by adding medium (13.5 mL) to each vial. The vials were sufficient for 7 scheduled sampling intervals plus 1 additional sampling interval if it was necessary to extend the test.
- After all of the test vessels had been filled, the vessels were sealed with butyl rubber septa and aluminium crimp caps then covered in aluminium foil.
- Test vessels were placed in the environmental chamber and incubated in the dark for 28 days.
- On a weekly basis, all test vessels were mixed by gently swirling.

TEMPERATURE MONITORING
- The temperature of the environmental chamber was monitored continuously during the exposure period using a Fisher Scientific digital minimum-maximum thermometer.
Reference substance:
benzoic acid, sodium salt
Remarks:
Lot 42K0011; Total organic carbon calculated to be 58.35 % based on the empiurical formula C7H5NaO2
Test performance:
INORGANIC CARBON ANALYSIS OF THE HEADSPACE
- Inorganic carbon evolved from the test medium of each test substance, reference substance and control is shown in Table 2 (attached) for each sample day.
- The results were used to calculate the amount of carbon dioxide evolved for each test substance and control (see Table 3, attached).
- Ultimate biodegradation data are presented in Table 4 (attached) and summarised graphically in Figure 1 (attached).
- The test item was found to be readily biodegradable because it was mineralised to > 60 % CO2 within a 10-day window of reaching 10 % CO2 evolution.
Key result
Parameter:
% degradation (CO2 evolution)
Remarks:
mean value
Value:
60.55
St. dev.:
4.17
Sampling time:
28 d
Remarks on result:
other: > 60 % CO2 within a 10-day window of reaching 10 % CO2 evolution
Details on results:
TEST CONDITIONS
- The daily temperature recorded in the environmental chamber during the study ranged from 20.8 to 21.7 °C.
Results with reference substance:
- Biodegradation of sodium benzoate increased rapidly and steadily during the first week of the study.
- Ultimate biodegradation subsequently peaked in the range 96 to 111 % from day 7 to day 28.
- Sodium benzoate can be considered to be readily biodegradable under the OECD criterion since > 60 % was produced within a 10-day window after reaching 10 % CO2 production.
- In addition, the rapid and extensive biodegradation of sodium benzoate confirmed the presence of an active and viable microbial population.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test material was found to be readily biodegradable because it was mineralised to > 60 % CO2 within a 10 -day window of reaching 10 % CO2 evolution.
Executive summary:

A GLP study was performed to determine the potential for biodegradation of the test item in water over 28 days using the carbon dioxide evolution method based on the ASTM E 1720 -95 Sealed Vessel, ISO/DIS-14593 Headspace and the OPPTS 835.3120 CO2 Evolution Biodegradation Test guidelines. The test material was found to be readily biodegradable because it was mineralised to > 60 % CO2 within a 10 -day window of reaching 10 % CO2 evolution. Biodegradation of the reference substance, sodium benzoate, increased rapidly and steadily during the first week of the study. Ultimate biodegradation subsequently peaked in the 96 to 111 % CO2 range from day 7 to day 28. Since > 60 % CO2 was produced within a 10 -day window after reaching 10 % CO2 production, sodium benzoate can be considered readily biodegradable under the OECD criterion. In addition, the rapid and extensive biodegradation of sodium benzoate confirmed the presence of an active and viable microbial population.

Description of key information

The test material was found to be readily biodegradable because it was mineralised to > 60 % CO2 within a 10 -day window of reaching 10 % CO2 evolution (ASTM E 1720 -95, ISO/DIS-14593 and OPPTS 835.3120).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A GLP study was performed to determine the potential for biodegradation of the test item in water over 28 days using the carbon dioxide evolution method based on the ASTM E 1720 -95 Sealed Vessel, ISO/DIS-14593 Headspace and the CO2 Evolution Biodegradation Test guidelines. The test material was found to be readily biodegradable because it was mineralised to > 60 % CO2 within a 10 -day window of reaching 10 % CO2 evolution. Biodegradation of the reference substance, sodium benzoate, increased rapidly and steadily during the first week of the study. Ultimate biodegradation subsequently peaked in the 96 to 111 % CO2 range from day 7 to day 28. Since > 60 % CO2 was produced within a 10 -day window after reaching 10 % CO2 production, sodium benzoate can be considered readily biodegradable under the OECD criterion. In addition, the rapid and extensive biodegradation of sodium benzoate confirmed the presence of an active and viable microbial population.