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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:
27 Feb - 27 Mar 2013
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: GLP guideline study with acceptable deviations.
Qualifier:
according to
Guideline:
other: Circular on the test method of new chemical substances (Japan) for biodegradability test by microorganism
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
mixture of sewage, soil and natural water
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Activate sludge was obtained by Chemicals Evaluation and Research Institute, Japan on January 11, 2013.
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
DOC removal
Parameter followed for biodegradation estimation:
test mat. analysis
Remarks:
(oxalate and ammonium ions, as well as element of Nb)
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Test temperature: 25 °C
- pH: measured at the end of the study

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

SAMPLING
- Sampling frequency: continuously for 28 days

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes

Reference substance:
aniline
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Parameter:
% degradation (DOC removal)
Value:
104
Sampling time:
28 d
Parameter:
% degradation (test mat. analysis)
Value:
100
Sampling time:
28 d
Remarks on result:
other: oxalate ion
Parameter:
% degradation (test mat. analysis)
Value:
ca. 2
Sampling time:
28 d
Remarks on result:
other: Ammonium ion (NH4)+
Details on results:
Residual rate of oxalate ion was 0% (mean) in test substance with sludge and 98% in test water with water.
Residual rate of ammonium ion was 96% (mean) in test substance with sludge and 98% in test water with water.
Residual rate of niobium ion was 0% (mean) in test substance with sludge and 101% in test substance with water.
Production rate of niobium hydroxide (V) was 103% (mean) in test substance with sludge.
Mass balance of niobium ion and niobium hydroxide (V) was 103% (mean) in test substance with sludge.
Results with reference substance:
The oxygen consumption for aniline in the above used test system reached 68.2% degradation after 14 days.

No (0%) oxygen consumption was observed after 28 days. The test substance is water soluble and dissociates into oxalic acid, ammonium ion and niobium ion. The residue amount of oxalic acid, ammonium ion and niobium (element) at the end of study was determined using liquid chromatography (LC) and ion chromatography (IC) and ICP in the test solutions and water controls respectively. The primary degradations of each component were as below:

Oxalic acid (oxalate ions): The residual amount of oxalic acid was 0 in test solutions containing inoculum and 98% in test substance with water, degradation rate is > 99%.

Ammonium ions: Residual rate of ammonium ion was 96% in the test solutions and 98% in water control; degradation rate is below than 2%.

Niobium (element): Residual rate of niobium ion according to ICP was 0 in the aqueous phase of test solutions and 101% in water control. As inorganic element, niobium undergo transformation and forms insoluble niobium(V) hydroxide based on the result of a preliminary test, filtered residue of solutions after exposure was determined analyzed by IR and compared with IR spectrum of standard substance of niobium(V) hydroxide.

DOC residual rate was 0% in average in test substance with sludge and 95% in test substance in water. Biodegradability was 104% in average. Residual amount of inorganic carbon in test substance with sludge was 0.8 mg in average.

According to the result, the organic component of oxalic acid that was derived from the test substance was degraded by microorganism and carbon dioxide generated by degradation remained in the test water as inorganic carbon.

The real mineralization ratio was calculated as 'mineralization ratio = degradation rate by oxygen consumption (%) + residual rate of inorganic carbon (percentage of residual inorganic carbon against theoretical DOC) (%)'. The mineralization ratio was 18% in average.

Since theoretical oxygen consumption of ANO was 2.8 mg and theoretical DOC was 4.3 mg and the values are very small, large variations in measured values resulted in lower mineralization than expected. This is the reason why mineralization ratio (18% in average) didn't reach to 60% which is the criterion as easy degradability. However, under this test condition, test substance was readily degraded into organic component and inorganic moiety, where the organic component was completely mineralized, inorganic moiety transformed into insoluble niobium(V) hydroxide. Ammonium ion remained unchanged in the test system.

 

Furthermore, the presence of niobium ion and ammonium ion didn't affect the biodegradability of oxalic acid ion which is an organic component.

Interpretation of results:
readily biodegradable

Description of key information

Organic moiety: > 99% in 28 days based on test material analysis and DOC removal

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The test substance is water soluble and dissociates into oxalic acid, ammonium ion and niobium ion. The residue amount of oxalic acid, ammonium ion and niobium (element) at the end of study was determined using liquid chromatography (LC) and ion chromatography (IC) and ICP in the test solutions and water controls respectively.

No oxygen consumption was observed after 28 days. > 99% of organic component oxalate is removed based on test material analysis and DOC removal. The inorganic moiety (niobium species) undergoes hydrolysis and forms insoluble niobium hydroxide. Removal of ammonium ion is less than 2%. Presence of niobium did not inhibit the activity microorganism and biodegradation rate of oxalate ions.