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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
Study period:
Jan 21 to Jun 26, 2015
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
other: HJ/f 153-2004, The guidelines for the testing of chemicals [S]. Beijing: SEPA, 2004
Qualifier:
equivalent or similar to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Version / remarks:
1992
Deviations:
no
Qualifier:
equivalent or similar to
Guideline:
EU Method C.4-E (Determination of the "Ready" Biodegradability - Closed Bottle Test)
Qualifier:
equivalent or similar to
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
GLP compliance:
yes
Remarks:
According to the guidelines of chemical testing good laboratory practices in China
Specific details on test material used for the study:
Test substance H6362
Lot No: 6F11027000
Purity 96%
Expiry: 2 years
Appearance: Clear high boiling odorless liquid
Storage conditions: Keep container tightly closed. Store away from heat and light.
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, domestic, non-adapted
Details on inoculum:
Samples of secondary effluent were obtained as the test inoculum from a sewage plant treating predominantly domestic sewage (Nanjing Chengdong Sewage Treatment Plant).

On the day of the test, the test inoculum was prepared by filtering the sample of sewage effluent through a coarse filter, (discarding the first 200 mL) and collecting the remaining filtrates. This inoculum was maintained under aerobic conditions in hte test area unitl use. The inoculum was not pre-conditioned at test temperature and was not pre-adapted to the test item. The test solutions were prepared in an inorganic mineral medium, inoculated with a small number of micro-organisms from a mixed population.
Duration of test (contact time):
ca. 28 d
Initial conc.:
ca. 2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of test medium: inorganic mineral medium
- Test temperature: 20°C
- pH: 6.68-7.03
- pH adjusted: no
- Aeration of dilution water: Dilution medium prepared by adding 1 mL each of the 4 stock solutions, prepared in pre-aerated deionized water to each litre of deionised water
- Suspended solids concentration: Not specified
- Continuous darkness: yes
- Other:

TEST SYSTEM
- Culturing apparatus: BOD-bottle
- Number of culture flasks/concentration: 4 groups (inoculum control, test group, procedure control, toxicity control): 4 bottles for toxicity control; 20 bottles for each of inoculum control, test group, and reference control
- Method used to create aerobic conditions: Laboratory supply of oil-free compressed air. BOD bottles aerated with hose which reached down to the bottom of the bottle
- Measuring equipment: Analytical balance, dissolved oxygen (DO) meter, pH meter
- Test performed in closed system: Yes, the BOD bottles were fully filled (total volume: 300 mL)
- Other: Test inoculum prepared by fiiltering sample of sewage effluent through coarse filter (first 200 mL discarded) and collecting remaining filtrates

SAMPLING
- Sampling frequency: DO measured made at 0, 2, 5, 7, 11, 14, 18, 21, 25 and 28 days (except for toxicity control - DO, pH, and temp taken at the start and after 14 days)
- Sampling method: DO meter
- Sample storage before analysis: Not specified

CONTROL AND BLANK SYSTEM
- Inoculum blank: contained inoculum only; O2 consumption reached 1.02 mg O2/L after 14d of incubation. Met the test criteria of <1.5 mg O2/L
- Procedure control: contained reference substance and inoculum; biodegradation of reference substance reached 91.6% w/in 14d. Met the test criteria of achieving 60% w/in 14d
- Toxicity control: contained test substance, reference substance, and inoculum. Degradation was 70.3% after 14d. Met the test criteria of no less than 25% in 14d.


STATISTICAL METHODS: Theoretical oxygen demand, oxygen consumption, and % biodegradability calculated
Reference substance:
benzoic acid, sodium salt
Remarks:
sodium benzoate
Key result
Parameter:
% degradation (O2 consumption)
Value:
ca. 73.3
Sampling time:
28 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
69.65
Sampling time:
25 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
68.6
Sampling time:
21 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
66
Sampling time:
18 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
64.6
Sampling time:
14 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
60.7
Sampling time:
11 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
56.2
Sampling time:
7 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
47.2
Sampling time:
5 d
Remarks on result:
other: average value
Parameter:
% degradation (O2 consumption)
Value:
5.32
Sampling time:
2 d
Remarks on result:
other: average value
Details on results:
The results showed that the average biodegradation rate of H6362 was 73.3% after 28-days and about 64% at 10-d window, based on the calculation of ThOD(NO3).
Results with reference substance:
The biodegradation of the reference substance achieved 91.6 % within 14 days.

The test is valid because the biodegradation of the reference substance achieved 91.6 % within 14 days, meeting the test criteria of achieving 60% within 14 days. Oxygen consumption in inoculated blanks was 1.02 mg O2/L after 14 days of incubation, meeting the test criteria of less than 1.5 mg O2/L. Degradation in the toxicity control was 70.3% after 14 days, meeting the test criteria of no less than 25% in 14 days. The result indicated that the test substance was not toxic to the inoculum. Additionally, the lowest level of dissolved oxygen in test substance group was 2.99 mg O2/L, which did not fall below 0.5 mg O2/L and the difference of biodegradation of the test item in the two replicates was less than 20%. Thus, all validity criteria listed in Section 4.4 were met. Therefore the test is considered valid.

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The study results showed that under the valid conditions, the average biodegradation rate of the test item was 73.3% after 28-days and about 64 % at the 10-d window. It would therefore be considered readily biodegradable, as it achieved the 10-d pass level (60% ThOD) stated in the OECD 301 Method.
Executive summary:

The study results showed that under the valid conditions, the average biodegradation rate of the test item was 73.3% after 28-days and about 64% at the 10-d window. It would therefore be considered readily biodegradable, as it achieved the 10-day pass level (60% ThOD) stated in the OECD 301 Method.

Description of key information

The results showed that the average biodegradation rate of H6362 (test substance) was 73.3% after 28-days and about 64% at 10-day window, based on the calculation of ThOD(NO3).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

The REACH Guidance on Information Requirements Chapter R.7b indicates that a pass level of 60% theoretical oxygen demand (ThOD; TG 301 C, TG 301 D and TG 301 F) obtained within 28 days, may be regarded as evidence of ready biodegradability. Therefore, the substance can be considered as readily biodegradable.