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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
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I))
GLP compliance:
no
Specific details on test material used for the study:
cyclohexanol
Oxygen conditions:
aerobic
Inoculum or test system:
mixture of sewage, soil and natural water
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): In March, June, September, and December, sludge was sampled at the following 10 places in Japan: 1. Fukogawa city sewage plant, 2. Fukashiba industry sewage plant, 3. Nakahama city sewage plant, 4. Ochiai city sewage plant, 5. Kitakami river, 6. Shinano river, 7. Yoshino river, 8. Lake Biwa, 9. Hiroshima bay, 10. Dookai bay; Sampling: 1. City sewage: Returned sludge from sewage plants was taken. 2. Rivers, lake and sea: Surface water and surface soil which were in contact with atmosphere were collected.- Method of cultivation: About 30 minutes after ceasing aeration to the sludge mixture, supernatant corresponding to about 1/3 of the whole volume was removed. Then the equal volume of dechlorinated water was added to the remaining portion and aerated again, followed by addition of synthetic sewage at a concentration of 0.1% (w/v). Synthetic sewage: Glucose, peptone and monopotassium phopsphate were dissolved in dechlorination water respectively. Each concentration was 5(W/V)% and the solution was adjusted to pH 7.0 +/- 1.0 with NaOH. This procedure was repeated once every day. The culturing was carried out at 25 ± 2 °C. 5 L of the filtrate of the supernatant of old activated sludge was mixed with 500 mL of the filtrate of the supernatant of new sludge and cultured at pH 7.0 ± 1.0 under sufficient aeration using prefiltered open air. During the cultivation, appearance of the supernatant, precipitability, formation of flock, pH, dissolved oxygen concentration in the solution and temperature were checked and necessary adjustments were made, Microflora in the activated sludge was microscopically observed and sludge with no abnormal symptom was used for the test. - Concentration of sludge: 30 mg/L
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS- Composition of medium: 3 mL each of four stock solutions, as described in JIS K 0102-1986-21, are diluted to 1000 mL with purified water; pH: 7.0Test solutions: a) (water + test substance): vessel containing 300 mL purified water into which 30 mg or 9 mg test substance was added. b) (sludge + test substance): vessel containing 300 mL basal culture medium into which 30 mg or 9 mg test substance was added; c) (sludge + aniline): vessel containing 300 mL basal culture medium into which 30 mg aniline test substance was added; d) (control blank): vessel containing 300 mL basal culture medium no further addition. The activated sludge was added to vessels b), c), D), that the concentration of suspended solid reached 30 mg/L or 100 mg/L.- pH adjusted: yes- Suspended solids concentration: determined according to Method Japanese Industrial Standards (JIS) K 0102-1986-14.1TEST SYSTEM- Culturing apparatus: Closed system oxygen consumption measuring apparatus (Coulometer: Ohkura Electric Co., Ltd.); 300 mL vessel, absorbent for evolving carbon dioxide Soda lime No .l (extra pure reagent, Wako Pure Chemical Industries, Ltd.).- Number of culture flasks/concentration: 1- Measuring equipment: Coulometer, Okhura Electric Co., Ltd.- Test performed in open system: no- Details of trap for CO2 and volatile organics if used: soda lime, extra pure, Wako Pure Chemical Industries, Ltd.)CONTROL AND BLANK SYSTEM- Inoculum blank: yes- Abiotic sterile control: yes- Toxicity control: no
Reference substance:
aniline
Preliminary study:
no information given
Test performance:
Preparation of test solutions:
A) Water plus Test substance: a vessel containing 300 mL of purified water into which 9 mg test substance was added
B) Sludge plus test substance: each vessel containing 300 mL basal culture medium into which 9 mg test substance was added
C) Sludge plus aniline: a test vessel containing 300 mL basal culture medium into which 30 mg of aniline was added.
D) Control Blank: a test vessel containing 300 mL basal culture medium.
Inoculation of activated sludge: the activated sludge cultivated as described above was so added to each test vessel B); c) and D), that the cocentration of suspended solid reached 30 mg/L in them. After termination of cultivation total organic carbon and the tset substance of samples (water + test substance) and (sludge + test substance) were measured.
Key result
Parameter:
% degradation (O2 consumption)
Value:
> 94 - < 99
Sampling time:
28 d
Details on results:
BOD was calculated via the following equation:Percentage of Biodegradation (%) = (BOD-B)*100/TOBwhere:BOD = Biological oxygen demand in sample (sludge + test substance)B = Biological oxygen demand in control blankTOD = Theoretical Oxygen demand required when the test substance was completely oxydized.
Results with reference substance:
No detailed information given:When percentage of aniline biodegradation calculated by BOD value was beyond 40% and 60% at the 7th and 14 th day, respectively, it was concluded that the test conditions were valid.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Cyclohexanol is readily biodegradable under these aerobic conditions according to guideline 301C: Modified MITI Test.
Executive summary:

The study was conducted according to OECD 301C; Modified MITI Test(I).

Sludge sampling was made at 4 different sewage treatment plants, 3 rivers, 1 lake and 2 bays in Japan at 4 different times in year.

The cultivation was done under aerated conditions at 25 ± 2 °C and pH was adjusted to 7.0 +/- 1.0 with NaOH.

Culturing apparatus: Closed system oxygen consumption measuring apparatus (Coulometer: Ohkura Electric Co., Ltd.)

Concentration of sludge: 30 mg/L and the concentration of cyclohexanol was100 mg/L. The cultivating duration was 28 days. The reference substance was Aniline.

BOD result for the test substance: 94 to 99% degree of degradation.

Description of key information

The substance is readily biodegradable according to OECD criteria, MITI (1992)

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Cyclohexanol was shown to be readily biodegradable in an OECD 301C test (MITI 1992) with degradation rates of 94 - 99% within 28 days. Although there is no statement whether the 10 day window criterion was fulfilled, the data are peer reviewed and published by Japanese authorities (Japan Chemical Industry Ecology-Toxicology & Information Center, JETOC) and are therefore considered as reliable for assessing the biodegradability of cyclohexanol. Furthermore, this result is supported by another test on ready biodegradability (OECD 301F) conducted with the structurally related substance cyclohexanone, in which more than 90% of cyclohexanone was degraded within 28 days (BASF AG 1998). In addition, a test on the inherent biodegradation (OECD 302B) is also available for cyclohexanol, showing 97% degradation within 7 days.

Under anaerobic test conditions, using an anaerobic methanogenic sludge adapted for degrading phenol and benzoate, cyclohexanol and cyclohexanone were not biodegradable at a temperature of 37 °C, over a test period of 23 days (Kobayashi 1989).