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Biodegradation in water: screening tests

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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:
Please refer to the Category Approach Justification provided in Section 13.
Reason / purpose:
read-across source
Related information:
Composition 1
Test material information:
Composition 1
Key result
Parameter:
% degradation (O2 consumption)
Value:
-5.5
Sampling time:
5 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
2.7
Sampling time:
15 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
14
Sampling time:
28 d
Details on results:
The test article displayed an inhibitory effect under these conditions.
Results with reference substance:
Ready biodegradability of the reference substance:
after 5 days = 54%
after 15 days = 57%
after 28 days = 75%
Validity criteria fulfilled:
no
Remarks:
: Inhibition test showed an inhibitory effect under the test conditions.
Interpretation of results:
other: can not be regarded as readily biodegradable.
Conclusions:
The reported results for the biodegradation of the sodium benzoate reference substance fell short of the OECD 301 D validation criterion of at least 60% in 14 days. A review of the calculation of these results from the O2 values provided in the appendix tables, according to the formula from the guideline cited in the report, showed that the value of m0 used for all the calculations was the mean day 0 value from the un-inoculated controls (10.0 mg/L). In comparison, the mean day 0 values for the inoculated blank, the reference substance and the test substance were 9.2, 9.8 and 8.8 mg/L, respectively. OECD 301 D directs that the day 0 value used should be that of the inoculated blank, except where this is different from the day 0 values of the test substance, when each calculation should use its own day 0 value. Recalculation of the biodegradation values in this way makes a marked difference to the results as follows:
Isopropyl chloride Sodium benzoate
Reported Recalculated Reported Recalculated
5 days -5.5% -16% 54% 72%
15 days 2.7% -8.2% 57% 75%
28 days 14% 2.7% 75% 93%
The recalculated reference substance biodegradation meets the validation criterion of at least 60% in 14 days. The overall outcome remains unchanged that, under the conditions of the test, the substance was not readily biodegradable and exerted an inhibitory effect on the inoculum.
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13 Sep - 12 Oct 1990
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Justification for type of information:
Please refer to the read-across justification document attached to section 13 in IUCLID.
Reference:
Composition 1
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
reliability scoring based on 1992 guideline
Deviations:
yes
Remarks:
test temperature was 20±1 ºC not 22±2 ºC; fails validity - inhibition test showed an inhibitory effect under the test conditions.
Qualifier:
according to
Guideline:
other: ECC Directive 79/831
GLP compliance:
yes
Test material information:
Composition 1
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated: domestic sewage treatment plant, Kläranlage Gümmerwald, Hannover, Germany
- Storage length: collected freshly on Day 0 of the test period
- Preparation of inoculum for exposure: Filtered through a paper filter. The first 200 mL were discarded and the rest of the filtrate was used for the test.
- Initial cell/biomass concentration: 5 x 10E5 CFU/mL (colony forming units)
Duration of test (contact time):
28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: Prepared according to the guideline OECD 301D.
- Test temperature: 20 ± 1 ºC
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 1000 mL volumetric flask
- Number of culture flasks/concentration: 3
- Measuring equipment: Oxi-meter (Oxi 96, WTW)

SAMPLING
- Sampling frequency: Oxygen content was measured on Day 0, 5, 15, and 28.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 3 replicates
- Abiotic sterile control: 3 replicates
- Toxicity control: 3 replicates
Reference substance:
benzoic acid, sodium salt
Remarks:
reported as sodium benzoate
Key result
Parameter:
% degradation (O2 consumption)
Value:
-5.5
Sampling time:
5 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
2.7
Sampling time:
15 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
14
Sampling time:
28 d
Details on results:
The test article displayed an inhibitory effect under these conditions.
Results with reference substance:
Ready biodegradability of the reference substance:
after 5 days = 54%
after 15 days = 57%
after 28 days = 75%
Validity criteria fulfilled:
no
Remarks:
: Inhibition test showed an inhibitory effect under the test conditions.
Interpretation of results:
other: can not be regarded as readily biodegradable.
Conclusions:
The reported results for the biodegradation of the sodium benzoate reference substance fell short of the OECD 301 D validation criterion of at least 60% in 14 days. A review of the calculation of these results from the O2 values provided in the appendix tables, according to the formula from the guideline cited in the report, showed that the value of m0 used for all the calculations was the mean day 0 value from the un-inoculated controls (10.0 mg/L). In comparison, the mean day 0 values for the inoculated blank, the reference substance and the test substance were 9.2, 9.8 and 8.8 mg/L, respectively. OECD 301 D directs that the day 0 value used should be that of the inoculated blank, except where this is different from the day 0 values of the test substance, when each calculation should use its own day 0 value. Recalculation of the biodegradation values in this way makes a marked difference to the results as follows:
Isopropyl chloride Sodium benzoate
Reported Recalculated Reported Recalculated
5 days -5.5% -16% 54% 72%
15 days 2.7% -8.2% 57% 75%
28 days 14% 2.7% 75% 93%
The recalculated reference substance biodegradation meets the validation criterion of at least 60% in 14 days. The overall outcome remains unchanged that, under the conditions of the test, the substance was not readily biodegradable and exerted an inhibitory effect on the inoculum.

Description of key information

Not readily biodegradable (activated sludge, OECD 301 D)

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

As no ready biodegradability study is available for assessing the biodegradation in water, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances, a read-across to the structurally related 2 -Chloropropane (CAS 75-29-6) was applied. The read across is justified due to the structural similarity of the analogue substances and similar physico-chemical properties resulting in a similar environmental fate and ecotoxicity profile. Further justification is given in the analogue justification attached to section 13 in IUCLID.

There is one GLP study available investigating the biodegradation of a structural analogue of the test substance in water according to the OECD guideline 301 D for the closed bottle test, suitable for insoluble and volatile substances.

In aerobic conditions, activated sludge from a local, domestic sewage treatment plant was inoculated with a nominal concentration of 2 mg/L of the test substance for 28 d in the dark. The degradation of the test substance was determined by measuring the actual O2concentration in the test bottles in regular intervals during the test. An inoculum blank, toxicity control and reference item were run in parallel. The calculation of the % biodegradation of the test/reference substance was based on the theoretical oxygen demand (ThOD).

Results indicated that the test substance displayed an inhibitory effect on the activated sludge under these conditions. The biodegradability of the reference item was 57 % after 15 d and 75% after 28 d. Hence, the reference compound did not reach the defined pass level by Day 14 (60% of ThOD). The biodegradability of the test substance was -5.5% after 5 d, 2.7% after 15 d and 14% after 28 d. From this it was concluded that the test substance cannot be regarded as readily biodegradable. 

However, a recalculation of the biodegradation using the respective Day 0 values of oxygen concentration for the test substance, reference substance and inoculum blank (instead of the Day 0 values of the un-inoculated control only), yielded markedly different results, which fulfilled the validity criterion of at least 60% after 14 d. Nonetheless, the overall outcome remained unchanged and the test substance was not readily biodegradable under the test conditions (2.7% after 28 d).