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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:
10 March 1999 - 12 April 1999
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
(1992)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of activated sludge: a biological waste water treatment plant treating predominantly domestic sewage (City of Geneva, Aire, Switzerland)
- Preparation of inoculum for exposure: sludge was collected in the morning, washed three times in mineral medium (by centrifuging at 1000 g for 10 minutes, discarding the supernatant and resuspending in mineral medium); kept aerobic until being used on the same day
- Concentration of sludge (suspended solids): 3.386 g/L
Duration of test (contact time):
32 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: According to Guideline 301 F. Water used to prepare the medium contained less than 10 mg/L of dissolved organic carbon.
- Test temperature: 22°C
- pH: at t=0 d: 7.42, at test end (t=32 d): 7.42-8.08
- pH adjusted: no
- Suspended solids concentration: 30 mg/L (dry weight)
- Continuous darkness: not reported

TEST SYSTEM
- Culturing apparatus: Water bath of the SAPROMAT D 12 respirometer
- Number of culture flasks/concentration: 2
- Measuring equipment: SAPROMAT D 12 (J.M. VOITH GmbH, D-7920, Heidenheim, Germany)
- Test performed in closed vessels: yes
- Details of trap for CO2: Soda lime (approx. 2g) was placed in an attachment of the stopper

SAMPLING
- Sampling frequency: Oxygen consumption of each flask was measured daily
- pH was measured at test initiation (in mineral medium) and at test end (after 32 days, in each flask)

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: yes
Reference substance:
benzoic acid, sodium salt
Remarks:
purity: min. 99.0%
Parameter:
% degradation (O2 consumption)
Value:
18
Sampling time:
2 d
Parameter:
% degradation (O2 consumption)
Value:
29
Sampling time:
5 d
Parameter:
% degradation (O2 consumption)
Value:
38
Sampling time:
12 d
Parameter:
% degradation (O2 consumption)
Value:
49
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
71
Sampling time:
28 d
Remarks on result:
other: 76% degradation after 32 days (end of test period)
Details on results:
Based on the percent degradation of sodium benzoate when tested in combination with the test substance (toxicity control), it is concluded that the test substance is not toxic to microorganisms at a concentration of 100 mg/L (>25% degradation based on ThOD).

- Validity criteria:
1. Not more than 20% difference between replicates of the flasks containing the test substance was reported.
2. The percentage degradation of the reference substance was 85% after 14 days.
3. In the toxicity control, >25% degradation occurred within 14 days, thus the test substance was not toxic to microorganisms at a test concentration of 100 mg/L.
4. Oxygen consumption of the inoculum blank was not greater than 60 mg/L in 28 days (22.0 mg O2/L).
Results with reference substance:
- Sodium benzoate (ThOD is 1.67 mg O2/mg): 71% degradation after 7 days and 85% after 14 days was achieved. Therefore, validity criteria was met.

Biodegradation of the test substance appears to take place in phases; a first biodegradation steps starts immediately and reaches 43% on day 18. Then, a second step starts and reaches 76% at the end of the test (32 days). Similar behaviour is observed in the toxicity control flasks. See graphs under 'Attached background material'.

In view of the > 70 % biodegradation in a test with strictly controlled conditions it can be assumed that the substance is readily biodegradable despite failing the 10-day window. This conclusion is motivated by using the criterion in CLP (2011, http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2011:083:FULL:EN:PDF), section 4.1.9.2.5 b). Here it is presented that if a substance is a multi-constituent the 10-day window does not need to be considered for ready biodegradability.

Validity criteria fulfilled:
yes
Remarks:
85% biodegradation of reference substance after 14 days; oxygen uptake of incoulum blank is <60 mg/L in 28 days; not more than 20% difference between replicates of the flasks containing the test substance
Interpretation of results:
readily biodegradable
Conclusions:
The substance showed 71% biodegradation after 28-days and 76% biodegradation after 32 days in an OECD TG 301F test.
Executive summary:

The ready biodegradability of the substance was investigated in a study conducted in accordance with OECD TG 301 F (1992, Manometric Respirometry) and GLP. The concentration tested was 100 mg/l test substance, with an activated sludge concentration of 30 mg/L. The test substance biodegraded for 71% after 28 -days and 76% after 32 days and it was not toxic to the inoculum. In view of the pass level of > 70% after 28 -days and the substance is a multi-constituent the substance is considered to be readily biodegradable.

Description of key information

The ready biodegradability of the substance was investigated in a study conducted in accordance with OECD TG 301 F (1992, Manometric Respirometry) and GLP. The concentration tested was 100 mg/l test substance, with an activated sludge concentration of 30 mg/L. The test substance biodegraded for 71% after 28 -days and 76% after 32 days and it was not toxic to the inoculum. In view of the pass level of > 70% after 28 -days the substance is considered to be ready biodegradable. In addition, the substance is a multi-constituent and the 10 -day window does not need to be met for passing the ready biodegradability criterion.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

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