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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
22 Oct - 19 Nov 1991
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: see 'Remark'
Remarks:
GLP-Guideline study with acceptable restrictions (The degradation in one replicate was below the pass level and differed by > 20%. However, the mean biodegradation based on BOD was > 70% (replicate 1: 88.5%; replicate 2: 51.56%; replicate 3: 84.79%). Moreover, the primary degradation measured by HPLC was 83, 74 and 100% in the three test vessels supports the assumption that the substance is readily biodegradable according to the OECD criteria. Therefore, the study is considered to be valid.
Qualifier:
according to
Guideline:
OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I))
Deviations:
yes
Remarks:
pH was not measured at the end of the study
Qualifier:
according to
Guideline:
other: Circular on Test Methods of New Chemical Substances (Japan), Biodegradation test
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: mixture of activated sludge from STP with freshwater from rivers and lakes, marine water and marine sediment
Details on inoculum:
- Source of inoculum/activated sludge: location: 10 sites (4 sewage plants, 3 rivers, 1 lake and 2 bays) around Japan; Sampling depth: return sludge in sewage plants, surface water and surface soil of foreshore.
- Laboratory culture: Thirty minutes after stopping of aeration, discard about one third of the whole volume of supernatant and add an equal volume of a solution (pH adapted to 7.0 with NaOH) containing 0.1% each of glucose, peptone and pottasium orthophosphate, to the settled material and re-commence aeration. This procedure was repeated once per day.
- Temperature: 25 ± 2 °C
- Storage conditions: observed appearance and general condition of sludge, determined sediments, pH, temperature and dissolved oxygen and observed with a light microscope, if it is normal.
- Storage length: started to use: 15 Oct 1991
- Concentration of sludge: 3900 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
Parameter followed for biodegradation estimation:
DOC removal
Parameter followed for biodegradation estimation:
test mat. analysis
Details on study design:
TEST CONDITIONS
- Composition of medium: recommended medium in the guideline
- Test temperature: 25 ± 1 °C
- Suspended solids concentration: 30 mg/L

TEST SYSTEM
- Culturing apparatus: closed oxygen consumption measuring machine with 300 mL culture bottle
- Number of culture flasks/concentration: 1 (water + test substance), 3 (sludge + test sub.), 1 (sludge + reference sub.), 1 (sludge)
- Measuring equipment: Coulometer
- Details of trap for CO2 and volatile organics if used: soda lime

SAMPLING
- Sampling frequency: Continuously
- Sterility check if applicable: no

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, 1 bottle
- Abiotic sterile control: no
- Toxicity control: no
Reference substance:
aniline
Parameter:
% degradation (O2 consumption)
Value:
75.3
Sampling time:
28 d
Parameter:
% degradation (test mat. analysis)
Value:
86
Sampling time:
28 d
Details on results:
No 10-day window required. Substance was readily biodegradable.
Results with reference substance:
The oxygen consumption for aniline in the above used test system reached 60% and 72% degradation after 7 days and 14 days.

The degradation in one replicate was below the pass level (51.56%). However, the mean biodegradation based on BOD was > 70%. Moreover, the primary degradation measured by HPLC was 83, 74 and 100% in the three test vessels supports the assumption that the substance is readily biodegradable according to the OECD criteria.

Table 1. Result of BOD, DOC and HPLC after 28 days

 

water + test sub.

sludge + test sub.

Theoretical Amount

sample No. 6

sample No. 3

sample No. 4

sample No. 5

BOD (*1)

mg

0.0

85.0

49.5

81.4

96.0

DOC

mg

0.0

1.1

0.5

1.0

24.4

HPLC

mg

30.2

5.0

7.7

0.0

30

% (*2)

101

17

26

0

-

(*1) (sludge + test sub.) was calculated by subtracting blank values.

(*2) Residue percentage was calculated as followed.

Residue percentage = Residue amount (mg) / Theoretical amount (mg) x 100

Validity criteria fulfilled:
no
Remarks:
Biodegradation in one replicate differed by more then 20%.
Interpretation of results:
readily biodegradable
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
key study
Justification for type of information:
Refer to analogue approach justification in section 13.
Reason / purpose:
read-across source
Parameter:
% degradation (O2 consumption)
Value:
75.3
Sampling time:
28 d
Parameter:
% degradation (test mat. analysis)
Value:
86
Sampling time:
28 d
Details on results:
No 10-day window required. Substance was readily biodegradable.
Validity criteria fulfilled:
no
Remarks:
Biodegradation in one replicate differed by more then 20%.
Interpretation of results:
readily biodegradable
Conclusions:
The substance is readily biodegradable: 75.3% BOD after 28 d (301 C).

Description of key information

Readily biodegradable: 75.3% (BOD) within 28 d (OECD 301 C); read-across

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

There is no study available investigating the ready biodegradability ofFatty acids, C16 and C18-22 - unsatd., C16-18 and C18 unsatd. alkyl ester (CAS 90990-29-7). Therefore, read-across to the structurally related source substance docosyl docosanoate (CAS 17671-27-1) was conducted in accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5. The source substance is characterized by a similar fatty acid chain length (C18 - 20) as well as a similar alcohol component (C20 - 22) and is therefore considered a suitable representative for the assessment of the ready biodegradability of the target substance.A detailed analogue approach justification is provided in IUCLID section 13 of the technical dossier.

 

The study with the source substance docosyl docosanoate (CAS 17671-27-1) was conducted according to the OECD guideline 301 C and GLP under aerobic conditions, using a mixture of 3900 mg/L activated sludge from a STP, with freshwater from rivers, lakes, marine water and marine sediment as inoculum, with a nominal test item concentration of 100 mg/L. A biodegradation of 75.3% (BOD) was observed after 28 d. Since the substance reached the pass level for OECD 301 C (> 60% after 28 d, no 10-d window required) the source substance docosyl docosanoate (CAS 17671-27-1) is readily biodegradable according to the OECD criteria.

Based on the high degree of similarity between the structural and physico-chemical properties of the source and target substance, the target substance is expected to have a similar ecotoxicological profile as the source substance. Hence, it can be concluded that the target substanceFatty acids, C16 and C18-22 - unsatd., C16-18 and C18 unsatd. alkyl ester (CAS 90990-29-7)is readily biodegradable according to guideline criteria.