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Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: conducted according to accepted guidelines in a GLP-certified facility

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2006

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)

Test material

Reference
Name:
Unnamed
Type:
Constituent

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
sewage, domestic (adaptation not specified)
Details on inoculum:
A mixed population of sewage sludge micro-organisms was obtained on 22 July 2005 from the final effluent stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.
The sample of effluent was filtered through coarse filter paper (first approximate 200 ml discarded) and maintained on aeration in a temperature controlled room at 21±1°C prior to use.
The culture medium used in this study (see Appendix 2) was that recommended in the OECD Guidelines
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
100 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
For the purpose of the test the test material was dispersed directly in culture medium. An amount of test material (50 mg) was dispersed in culture medium (495 ml) prior to the addition of inoculum (5 ml) to give the test concentration of 100 mg/l. This method of preparation was chosen based on the results of preliminary solubility/dispersibility trials. A test concentration of 100 mg/l was selected for use in the test following the recommendations of the Test Guideline.
Data from the control vessels was shared with similar concurrent studies.
Analysis of the concentration, homogeneity and stability of the test material in the test preparations were not appropriate to the Test Guideline.

For the purposes of the test a standard material, aniline (C6HsNH2) (Sigma Lot No 033K01651), was used. An initial stock solution of 1000 mg/l was prepared by dissolving the standard material directly in culture medium with the aid of ultrasonication for approximately 5 minutes. An aliquot (50 ml) of this stock solution was diluted with culture medium (445 ml) and inoculum (5 ml), to give the test concentration of 100 mg/l. The volumetric flask containing the stock solution was inverted several times to ensure homogeneity.

For the purposes of the test a toxicity control, containing the test material and aniline, was prepared in order to assess any toxic effect of the test material on the sewage treatment microorganisms used in the test. An amount of test material (50 mg) was dispersed in culture medium (445 ml) prior to the addition of an aliquot (50 ml) of the aniline stock solution and inoculum (5 ml) to give the test concentrations of 100 mg/1.

The following test preparations were prepared and inoculated in 500 ml bottles:
a) Four replicate bottles containing inoculated culture medium to act as the control.
b) Three replicate bottles containing inoculated culture medium and the standard material, aniline, at a concentration of 100 mg/l.
c) Three replicate bottles containing inoculated culture medium and the test material at a concentration of 100 mg/l.
d) Two replicate bottles containing inoculated culture medium, the standard material, aniline, at a concentration of 100 mgll and the test material at a concentration of 100 mg/l to act as toxicity control vessels.
All vessels were inoculated with the prepared inoculum at a rate of 1 % vlv.
On Day 0, DOC analyses were carried out on one control and one standard material vessel.
DOC analysis of the test material preparations was not conducted as the preliminary work conducted indicated that, when using the method of preparation employed in the test, the test material would not completely dissolve. It was therefore considered that DOC analysis of the test material preparations would give misleading results.
On Day 28, DOC analyses were carried out on two control and one standard material vessels.
Reference substance
Reference substance:
aniline
Remarks:
100mg/l

Results and discussion

Test performance:
The BOD of the inoculated culture medium (control) was 16.72 mg 02/1 after 28 days and therefore satisfied the validation criterion given in the OECD Test Guidelines.
The pH of the inoculated test vessels on Day 28 ranged from 7.8 to 8.5 and hence satisfied the validation criterion given in the OECD Test Guidelines.
The difference between extremes of replicate BOD values at the end of the test was <20% and therefore satisfied the validation criterion given in the OECD Test Guidelines.
Aniline attained 70% degradation after 14 days and 75% degradation after 28 days thereby confirming the suitability of the inoculum and test conditions.
Aniline attained 102% degradation after 28 days, calculated from the results of the DOC analyses performed on Days 0 and 28. The extent of aniline degradation calculated from DOC analyses was higher than that calculated from biological oxygen demand (BOD). Whereas the DOC analyses can indicate the combined extent of both biotic and abiotic degradation processes, the measured BOD value can be attributed solely to biological degradation (mineralisation). Therefore, the difference between these metrics may be attributed to abiotic removal processes such as adsorption or covalent binding to biosolids, which could reduce the amount of aniline available for biological degradation.
% Degradation
Parameter:
% degradation (O2 consumption)
Value:
23
Sampling time:
28 d
Details on results:
The test material attained 23% degradation after 28 days (replicate values 22% and 24%), calculated from the oxygen consumption values, and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301F.
The toxicity control attained 33% degradation after 14 days and 64% degradation after 28 days thereby indicating that under the strict terms and conditions of the OECD Guidelines the test material was not toxic to the sewage treatment micro-organisms used in the study.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
inherently biodegradable, not fulfilling specific criteria
Conclusions:
The test material attained 23% degradation after 28 days (replicate values 22% and 24%), calculated from the oxygen consumption values, and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301F.