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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:
12 December 1996 - 25 November 1998
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study with acceptable restrictions.
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): aliquot of fresh activated sludge from a domestic wastewater treatment plant in New Jersey, USA

- other: 10^6 CFU/mL

- sludge was obtained on day 1 of test
- total suspended solids of the sludge was determined to be 3.02 g/L.
- sludge was homogenized, the homogenated sample was allowed to settle for 30 min, and the supernatant was decanted and used for final preparation. The supernantant was added at a 1% loading volume of sludge to test medium.
Duration of test (contact time):
70 d
Initial conc.:
49 - 57 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS

- Test temperature: 22 ± 1°C
- Composition of medium: Activated sludge and test medium were combined prior to test material addition. Test medium consited of glass distilled water and mineral salts (Phosphate buffer, Ferric chloride, Magnesium sulfate, Calcium chloride)

TEST SYSTEM
- Culturing apparatus: test vessels were 1L glass flasks placed in a waterbath and electronically monitored for oxygen consumption
- Other: Triplicate test system for test material. Duplicate test system for positive control at approx. concentrations of 51 mg/L through day 28

SAMPLING
- Sampling frequency: continuously monitored by an automated respirometer during a 70 day testing period
Reference substance:
benzoic acid, sodium salt
Test performance:
Sodium benzoate achieved 80.31% biodegradation with a standard deviation of 0.95% by day 14. Therefore the test is considered valid.
Parameter:
% degradation (O2 consumption)
Value:
10.5
St. dev.:
1.66
Sampling time:
15 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Parameter:
% degradation (O2 consumption)
Value:
49
St. dev.:
1.81
Sampling time:
43 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Parameter:
% degradation (O2 consumption)
Value:
60.2
St. dev.:
0.82
Sampling time:
60 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Parameter:
% degradation (O2 consumption)
Value:
61.81
St. dev.:
1.34
Sampling time:
70 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Details on results:
The biodegradation half-life was < 7 weeks. 10% biodegradation of the test material was achieved on approx. day 15, 50% on approx. day 46.
Test material biodegradability mean at day 28 was 22.4% (21.8, 23,5, 21.8 %).
Test material biodegradability mean at day 70 was 61.81% (60.4, 63.0, 62.1 %).
Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
Hydrocarbons, C7-C9, isoalkanes, is inherently biodegradable under the conditions of the study and is not expected to persist in the environment under aerobic conditions.
Executive summary:

Hydrocarbons, C7-C9, isoalkanes, is inherently biodegradable under the conditions of the study and is not expected to persist in the environment under aerobic conditions.

Endpoint:
biodegradation in water: screening tests
Type of information:
experimental study
Adequacy of study:
key study
Study period:
20 February 1997 - 25 November 1998
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study with acceptable restrictions.
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Principles of method if other than guideline:
Based on OECD guideline 301F the test phase was prolonged for inherent testing.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): aliquot of fresh activated sludge from a domestic wastewater treatment plant in New Jersey, USA

-other: microbial activity of of inoculum: 10^5 CFU/mL

- Inoculum preparation for Inherent biodegradability testing: On day 70 of the ready biodegradability test, all systems were disassembled. The contents of MRD-96-587 test systems were centrifuged at 10,000 rpm for 20 min. The supernatant was poured off and filtered through a Whatman #4 filter. The solids were combined and then resuspended with a minimal volume of filtered supernatant.The final volume was ~ 150mL. The remaining supernatant was then filtered through 0.45 µm microfiber filters. The biomass solids remaining on the filter were gently scraped into the previous collected biomass. The harvested biomass was blended for approx. 2 min. Exactly 100 mL of the harvested biomass was added to 10mL of test medium. Each new blank, sodium benzoate and MRD-96-587 test system contained one liter of the inoculated test medium. The microbial activity of the inoculum was determined to be 100000 CFU/mL. The phase 2 inherent biodegradability test was the conducted for 75 days.
Duration of test (contact time):
75 d
Initial conc.:
ca. 49 - ca. 57 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS

- Test temperature: 22 ± 1°C
- Composition of medium: Activated sludge and test medium were combined prior to test material addition. Test medium consited of glass distilled water and mineral salts (Phosphate buffer, Ferric chloride, Magnesium sulfate, Calcium chloride)

TEST SYSTEM
- Culturing apparatus: test vessels were 1L glass flasks placed in a waterbath and electronically monitored for oxygen consumption
- Other: Triplicate test system for test material. Duplicate test system for positive control at approx. concentrations of 51 mg/L through day 28

SAMPLING
- Sampling frequency: continuously monitored by an automated respirometer during a 70 day testing period
Reference substance:
benzoic acid, sodium salt
Test performance:
In the inherent test sodium benzoate achieved 97.76% with a SD of 1.13% by day 14. Therefore the test is considered valid.
Parameter:
% degradation (O2 consumption)
Value:
64.06
St. dev.:
10.53
Sampling time:
75 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Parameter:
% degradation (O2 consumption)
Value:
60.3
St. dev.:
9.59
Sampling time:
42 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Parameter:
% degradation (O2 consumption)
Value:
51.3
St. dev.:
11.91
Sampling time:
28 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Parameter:
% degradation (O2 consumption)
Value:
26.83
St. dev.:
8.59
Sampling time:
11 d
Remarks on result:
other: MRD-96-587, Isopar C (U.S.); values based on ThOD of test material.
Results with reference substance:
>60% biodegradation by day 14
Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable
Conclusions:
Hydrocarbons, C7-C9, isoalkanes, is inherently biodegradable under the conditions of the study and is not expected to persist in the environment under aerobic conditions.
Executive summary:

Hydrocarbons, C7-C9, isoalkanes, is inherently biodegradable under the conditions of the study and is not expected to persist in the environment under aerobic conditions.

Description of key information

22% (28 days), 62% (70 days) (unacclimated)
51% (28 days), 64% (75 days) (acclimated)

Key value for chemical safety assessment

Additional information

A study is available using a standard OECD 301F manometric respirometry test procedure for one multi-constituent isoalkane substance (Exxon 1998). The results show that the substance is not readily biodegradable, but can demonstrate high extents of biodegradability when test durations are extended. The substance composed predominantly of isooctane isomers demonstrated 22 and 62% biodegradation after 28 and 70 days, respectively. A second study was conducted with this substance that used the acclimated inoculum from the previous study, harvested on day 70 (Exxon 1998). The results showed 51 and 64% biodegradation after 28 and 75 days, respectively.