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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:
06/07/1998 - 14/09/1998
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I))
Version / remarks:
1992
Deviations:
yes
Remarks:
Samples for DOC analysis were prepared by centrifugation at 1000 g for 10 min instead of centrifugation at 4000 g for 15 min or filtration through a 0.45 µm filter as specified in the guideline
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: mixture of domestic sewage, river water, lake water and bay water (ratio 4:3:1:2) - non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Samples were collected from 10 different sites in Japan. Of these 10 samples, 4 were collected from sewage treatment plants (Fushiko River treatment plant (Sapporo, Hokkaido), Nakahama treatment plant (Osaka city, Osaka Prefecture), Kashima treatment plant (Kashima, Ibaraki Prefecture), Ochiai treatment plant (Shinjuku-ku, Tokyo)). Further, 3 river samples (Kitakami River (Ishinomaki City, Miyagi Prefecture), Yoshino River (Tokushima City, Tokushima Prefecture), Shinano River (Nishikanbara District, Niigata Prefecture)), 1 lake sample (Lake Biwa (Otsu City, Shiga Prefecture)) and 2 bay water samples (Hiroshima Bay (Hiroshima City, Hiroshima Prefecture) & Dokai Bay (Kitakyushu City, Fukuoka Prefecture)) were collected.
- Sampling method: City sewage: Return sludges from sewage plants were collected; Rivers, lake and sea: Surface water and surface soil which are in contact with the atmosphere were collected
- Method of cultivation: aerobic
- Preparation of inoculum for exposure: 10 L of sludge mixture, mixed from samples collected at the 10 sites described above, was filtered and aerated for about 23.5 h. 30 minutes after stopping aeration, about one third of the supernatant was discarded and an equal amount of a dechlorinated water solution containing 0.1 % each of glucose, peptone and potassium hydrogen phosphate was added (pH adjusted to 7 ± 1 with NaOH). Aeration was restarted and this procedure was repeated once a day for a culturing period of 3 months (Temperature: 25 ± 2 °C; pH 7 ± 1). Afterwards, 5 L of filtered supernatant of the activated sludge cultured for 3 months were mixed with 5 L of a fresh, filtered sludge mixture (prepared from samples collected at the sites described above). The 10 L mixture was aerated after the pH was adjusted to 7 ± 1. The biological phase of the activated sludge was observed microscopically. The absence of abnormalities was confirmed and activated sludge was used for the test.
- Concentration of suspended solids in activated sludge after acclimation with synthetic sewage: 4200 mg/L
- Final test concentration of sludge: 30 mg/L suspended solids
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Remarks:
recorded as BOD (biochemical oxygen demand)
Parameter followed for biodegradation estimation:
DOC removal
Remarks:
Sample preparation not guideline-conform (see additional information)
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
TEST CONDITIONS
- Composition of medium (basal culture medium): 3 ml of each solution A, B, C and D (as specified in JIS K 0102-1993-21) was added to purified water to a final volume of 1 L and the pH was adjusted to 7.0.
- Test temperature: 25 ± 1 °C
- pH: 7.0
- pH adjusted: yes, pH in test vessels was adjusted to pH 7 prior to inoculation
- Aeration of dilution water: yes
- Suspended solids concentration: 30 mg/L
- Continuous darkness: not reported
- Other: the test solution was stirred by magnetic stirrer

TEST SYSTEM
- Culturing apparatus: Closed system oxygen consumption measuring apparatus; 300 ml culture flasks
- Number of culture flasks/concentration: 3 flasks for test substance + activated sludge; 1 flask for each control (test substance + water; reference compound aniline + activated sludge; activated sludge only)
- Measuring equipment: Coulometer: Ohkura Electric Co., Ltd.; Data sampler: Asahi Techneion Co., Ltd.
- Details of trap for CO2: soda lime

SAMPLING
- Sampling frequency: at days 7, 14, 21 and 28
- Sampling method: 10 ml were sampled with a pipette

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: yes
- Reference substance control: yes
- Toxicity control: no
Reference substance:
aniline
Test performance:
No unusual observations. The degree of decomposition of aniline calculated from BOD was 70 % after 7 days and 75 % after 14 days, which is in accordance with the validity criteria in OECD 301C.
Parameter:
% degradation (O2 consumption)
Value:
92
St. dev.:
2
Sampling time:
28 d
Remarks on result:
other: Average of three test vessels
Parameter:
% degradation (DOC removal)
Value:
97
St. dev.:
0.5
Sampling time:
28 d
Remarks on result:
other: Average of three test vessels
Remarks:
As samples for DOC analysis were prepared by centrifugation at 1000 g for 10 min, rather than at 4000 g for 15 min as specified in OECD301, it is uncertain whether measured values correspond to dissolved organic carbon.
Parameter:
% degradation (test mat. analysis)
Value:
100
St. dev.:
0
Sampling time:
28 d
Remarks on result:
other: HPLC analysis; average of three test vessels
Details on results:
In the abiotic control, significant oxygen consumption, DOC removal or test material removal was not observed.
In the blank inoculum control, a BOD of 6.4 mg after 28 days was observed.
Measurements of pH at test end ranged from 7.7 to 8.3 in test vessels with test substance and activated sludge. pH in the abiotic control (test substance + water) was 3.9 at the end of the test.
Results with reference substance:
The degree of decomposition of aniline calculated from BOD was 70 % after 7 days and 75 % after 14 days.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
A ready biodegradability modified MITI test (I) according to OECD guideline 301C was conducted for m-toluic acid for a duration of 28 days with an initial test substance concentration of 100 mg/L. The mean biodegradation calculated from BOD after 28 d was 92 % (SD: 2.0). Thus, the test substance m-toluic acid is considered to be readily biodegradable by fulfilling the pass level of > 60 % degradation (oxygen consumption). The 10-d window concept does not apply to the MITI method.
Additionally, degradation was calculated from DOC removal and test material analysis, which resulted in 97 % (SD: 0.5) and 100 % (SD: 0.0) biodegradation of m-toluic acid, respectively. However, results based on DOC removal cannot be considered fully reliable as samples for DOC analysis were prepared by centrifugation at 1000 g for 10 min rather than at 4000 g for 15 min as specified in OECD 301. Therefore, it is uncertain whether measured values correspond to dissolved organic carbon as defined in the test guideline.

Description of key information

m-Toluic acid is readily biodegradable (92 % after 28 days) based on a Ready Biodegradability Modified MITI test according to OECD 301C.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information