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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Justification for type of information:
Data is from peer reviewed journal
Qualifier:
according to guideline
Guideline:
other: as mentioned below
Principles of method if other than guideline:
Biodegradation study was conducted for evaluating the percentage biodegradability of test chemical.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
other: Bacteria
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Test inoculum i.e., bacteria was isolated from groundwater.
Duration of test (contact time):
28 d
Initial conc.:
1.484 mg/L
Based on:
test mat.
Remarks:
(1484 µg/l)
Parameter followed for biodegradation estimation:
test mat. analysis
Remarks:
(% degradation)
Details on study design:
TEST CONDITIONS
- Test temperature: 15°C

TEST SYSTEM
- Culturing apparatus: Chemostat
- Number of culture flasks/concentration: 3 replicates

CONTROL AND BLANK SYSTEM
Controls were also run simultaneously during the study.
Key result
Parameter:
% degradation (test mat. analysis)
Value:
96.6
Sampling time:
28 d
Remarks on result:
other: Other details not known
Details on results:
Test chemical undergoes 96.6% degradation after a period of 28 days.

Biotransformation of test chemical by several different microorganisms was initiated out via N-oxidation of the compound.

Table: Degradation of alkylpyridines in groundwater after 4 weeks of incubation in a chemostat.

Compound

Influent

Effluent

Uninoculated

Inoculated*

Test chemical

1484 µg/l

1105 µg/l

49 µg/l

 

Dilution rate of 0.067/day

Where

* = 1000000 cells/ml of a mixed culture capable of metabolizing 14 alkylpyridines

Validity criteria fulfilled:
not specified
Interpretation of results:
readily biodegradable
Conclusions:
The percentage degradation of test chemical was determined to be 96.6% after a period of 28 days. Thus, test chemical was considered to be readily biodegradable in water.
Executive summary:

Biodegradation study was conducted under aerobic conditions for evaluating the percentage biodegradability of test chemical. Bacteria isolated from groundwater was used as a test inoculum. Test chemical concentration/influent used for the study was 1.484 mg/l (1484 µg/l). Chemostat was used as a test vessel. All test vessels were incubated at a temperature of 15°C for a period of 28 days. Controls were also run simultaneously during the study. All experiments were performed in triplicates. The percentage degradation of test chemical was determined to be 96.6% after a period of 28 days. Thus, test chemical was considered to be readily biodegradable in water.

Description of key information

Biodegradation study was conducted under aerobic conditions for evaluating the percentage biodegradability of test chemical. Bacteria isolated from groundwater was used as a test inoculum. Test chemical concentration/influent used for the study was 1.484 mg/l (1484 µg/l). Chemostat was used as a test vessel. All test vessels were incubated at a temperature of 15°C for a period of 28 days. Controls were also run simultaneously during the study. All experiments were performed in triplicates. The percentage degradation of test chemical was determined to be 96.6% after a period of 28 days. Thus, test chemical was considered to be readily biodegradable in water.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Various experimental studies of the test chemical and supporting studies for its read across substance were reviewed for the biodegradation end point which are summarized as below:

 

In an experimental study from peer reviewed journal (Z. Ronen et. al., 1995), biodegradation experiment was conducted under aerobic conditions for evaluating the percentage biodegradability of test chemical. Bacteria isolated from groundwater was used as a test inoculum. Test chemical concentration/influent used for the study was 1.484 mg/l (1484 µg/l). Chemostat was used as a test vessel. All test vessels were incubated at a temperature of 15°C for a period of 28 days. Controls were also run simultaneously during the study. All experiments were performed in triplicates. The percentage degradation of test chemical was determined to be 96.6% after a period of 28 days. Thus, test chemical was considered to be readily biodegradable in water.

 

Another biodegradation study was conducted for evaluating the biodegradation potential of test chemical (from peer reviewed journal and REAXY's database). Microbial culture was used as a test inoculum and isolated by enrichment method. Enrichment cultures for test chemical degrading bacteria were initiated by inoculating 100 ml of mineral salt medium with 5 g of contaminated sediment 7.6 m below the soil surface.  Enrichment was achieved by successive transfers of cultures into fresh medium containing the appropriate test chemical every 2 weeks.  Single colonies were selected from the plates and further purified by repetitive streaking on the agar plates. Cultures were maintained on agar slants with the appropriate substrate and stored at 4°C. Isolated strains were examined for morphological and biochemical proper ties by the API 20NE kit (BioM´erieux, Lyon France). During the isolation of cultures, High performance liquid chromatography, HPLC, was used for analysis of the various compounds. Ammonium in the culture medium was analyzed with Nessler reagent. Dissolved organic carbon (DOC) was determined using a Dohrmann DC190 TOC analyzer (Rosemount Analytical Inc., Santa Clara, CA). Test chemical conc. used for the study was 78.22 mg/l (0.73 mM/l). Test inoculum was incubated with test chemical for 8 days. For mineralization study, in all of the cultures the respective substrate was not detected by HPLC at the end of the incubation period. Residual compound, dissolved organic carbon, and ammonium were determined. Test chemical undergoes 84% degradation by DOC removal analysis after 8 days. Degradation product was evaluated to be carbon dioxide and ammonium. The percentage degradation of test chemical was determined to be 84% degradation by DOC removal analysis after 8 days. Degradation product was evaluated to be carbon dioxide and ammonium. Thus, test chemical was considered to be readily biodegradable in water.

 

For the test chemical from peer reviewed journal (R.A. Pandey et. al., 1997), biodegradation study was conducted under aerobic conditions for evaluating the percentage biodegradability of test chemical. Activated sludge mixed with acclimatized mixed culture of Nocardia sp. was used as a test inoculum. Test inoculum samples were collected from CMAS and evaluated for other biological entities by following standard procedure. Test chemical concentration used for the study was 10.4 mg/l. Basal medium, Tryptone yeast extract broth and solid medium were used as a test medium. Additionally phosphate was added to the test medium. Glass reactor (2.5 lit with inbuilt settlers) was used as a test vessel. A glass reactor was fitted with glass diffuser for the aeration purpose. Watson Marlow feeding pump model No. 502 ' S ' was used for feeding of the wastewater to completely mixed activated sludge (CMAS) at controlled rate. For the detection of test chemical, gas chromatograph (GC) with make Perkin Elmer Model F-I7 fitted with Stainless Steel FFAP column was used in the study. Beckman's Total Organic Carbon analyser model No. 915 'A' was used for estimation of bases in terms of TOC. The completely mixed activated sludge (CMAS) process was operated at different hydraulic retention times (HRT) ranging from 15 to 96 hrs. The CMAS was monitored for mixed liquor suspended solid (MLSS), bases concentration by chromatographic method, TOC, and other parameters were monitored as per standard methods. The percentage degradation of test chemical was determined to be 99% after a period of 2 days (48 hrs). Thus, test chemical was considered to be readily biodegradable in water.

 

In a supporting weight of evidence study from handbook and authoritative database, biodegradation experiment was conducted for 21 days for evaluating the percentage biodegradability of test chemical. The study was performed according to OECD Guideline 302 B (Inherent biodegradability: Zahn-Wellens/EMPA Test) under aerobic conditions. Activated sludge obtained from municipal wastewater sewage plant was used as a test inoculum. The percentage degradation of test chemical was determined to be 13.3, 10.3, 26.8, 85.7 and 98.7% by DOC removal after 15 mins, 1 day, 3 day, 7 day and 21 days, respectively. Thus, based on percentage degradation, test chemical was considered to be readily biodegradable in water.

 

Additional biodegradation study was conducted for 28 days for evaluating the percentage biodegradability of test chemical (Secondary source, 2019). The study was performed following the OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test) under aerobic conditions. Test inoculum activated sludge was originated from domestic wastewater treatment plant located in Beerse, Belgium. Fresh sample was collected on the day of test initiation and the sludge was washed twice with tap water and once with dilution water (nutrient medium) to remove residual wastewater and potential inhibitory materials. The sludge was diluted to 30 mg suspended solids/l in the test solutions. Initial test chemical conc. used for the study was 20 mg/l. 5-l brown Jars. It has a holding capacity of approximately 3 l of the test solutions was used as a test vessels. Each jar was filled with nutrient medium and activated sludge and attached to aeration tubes and aerated with CO2-free air and gently stirred using magnetic stirrers for 72 hours to reduce the blank respiration rate. Either test substance or reference compound was added to the appropriate jars and CO2 scrubbing bottles were filled with sodium hydroxide and attached in series to the air exit tubes from the jars. Inoculum blank (containing nutrient medium and activated sludge) and abiotic sterile control (containing only medium) were also run simultaneously. Reference substance system contains medium, activated sludge and aniline (at a conc. 20 mg/l), respectively. All test vessels were incubated for 28 days at a temperature of 19 to 23°C. All test experiments were run in duplicates. On days 0, 1, 2, 3, 7, 10, 14, 17, 21, 24 and 28 samples from the jars were removed, centrifuged and analyzed for dissolved organic carbon (DOC) using an organic carbon analyzer. At the same time, the first CO2 scrubbing bottle was removed and the total inorganic carbon was analyzed. A new scrubbing bottle was added at the end of the series. The percentage degradation of test chemical was determined to be 95 and 85% by DOC removal and CO2 evolution parameter within 10 and 28 days, respectively. Thus, based on percentage degradation, test chemical was considered to be readily biodegradable in water.

 

For the test chemical from secondary source (IUCLID dataset, 2000), biodegradation experiment was conducted for 21 days for evaluating the percentage biodegradability of test chemical. The study was performed following the principles of the OECD Guideline 301 C (Ready Biodegradability: Modified MITI Test (I)) under aerobic conditions. Activated sludge (at a conc. of 30 mg/l as suspended solid) was used as a test inoculum. Initial test chemical conc. used for the study was 100 mg/l. Test substance undergoes 58% degradation by oxygen consumption (BOD) parameter in 21 days, and was reported to go on the upward trend after 21 days. Thus, concluded the test chemical as readily biodegradable in water.

 

Thus, on the basis of above results, it can be concluded that the test chemical was considered to be readily biodegradable in water.