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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:
key study
Study period:
11 July 2017 to 10 August 2017
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)
Deviations:
no
Qualifier:
according to
Guideline:
EPA OPPTS 835.3110 (Ready Biodegradability)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic (adaptation not specified)
Details on inoculum:
INOCULUM
- A mixed population of activated sewage sludge micro-organisms was obtained on 10 July 2017 from the aeration stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.

PREPARATION OF INOCULUM
- The activated sewage sludge sample was washed twice by settlement and re-suspension in mineral medium to remove any excessive amounts of dissolved organic carbon (DOC) that may have been present. The washed sample was then maintained on continuous aeration in the laboratory at a temperature of approximately 21 °C and used on the day of collection.
- Determination of the suspended solids level of the activated sewage sludge was carried out by filtering a sample (100 mL) of the washed activated sewage sludge by suction through pre-weighed 70 mm diameter Whatman GF/A filter paper (rinsed three times with 20 mL deionized reverse osmosis water prior to drying in an oven) using a Buchner funnel. Filtration was continued for a further 3 minutes after rinsing the filter three successive times with 10 mL of deionized reverse osmosis water. The filter paper was dried in an oven at approximately 105 °C for at least 1 hour and allowed to cool before weighing. The process was repeated until a constant weight was attained. The suspended solids concentration was equal to 2.8 g/L prior to use.
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
other: carbon
Parameter followed for biodegradation estimation:
CO2 evolution
Reference substance:
benzoic acid, sodium salt
Remarks:
Sigma Aldrich (Batch SLBT3039; Purity > 99.5 %; Expiry date 09 May 2022; Room temperature storage conditions over silica gel)
Key result
Parameter:
% degradation (CO2 evolution)
Value:
73
Sampling time:
28 d
Details on results:
DEFINITIVE TEST
- Inorganic carbon values for the test item, procedure control, toxicity control and inoculum control vessels at each analysis occasion are given in Table 1 (attached).
- Percentage biodegradation values of the test and reference items and the toxicity control are given in Table 2 (attached).
- The biodegradation curves are presented in Figure 1 (attached).
- Total and Inorganic Carbon values in the culture vessels on Day 0 are given in Table 3 (attached).
- The pH values of the test preparations on Days 0 and 28 are given in Table 4 (attached).
- Observations made on the contents of the test vessels are given in Table 5 (attached).

VALIDATION CRITERIA
- The total C02 evolution in the inoculum control vessels on Day 28 was 26.20 mg/L and therefore satisfied the validation criterion given in the OECD Test Guidelines.
- The IC content of the test item suspension in the mineral medium at the start of the test (see Table 3, attached) was below 5 % of the TC content and hence satisfied the validation criterion given in the OECD Test Guidelines.
- The difference between the values for C02 production at the end of the test for the replicate vessels was < 20 % and hence satisfied the validation criterion given in the OECD Test Guidelines.

BIODEGRADATION
- Acidification of the test vessels on Day 28 followed by the final analyses on Day 29 was conducted according to the methods specified in the Test Guidelines. This acidification effectively kills the micro-organisms present and drives off any dissolved CO2 present in the test vessels. Therefore any additional CO2 detected in the Day 29 samples originated from dissolved CO2 that was present in the test vessels on Day 28 and hence the biodegradation value calculated from the Day 29 analyses is taken as being the final biodegradation value for the test item.
- The results of the inorganic carbon analysis of samples from the first absorber vessels on Day 29 showed an increase in all replicate vessels.
- The test item attained 73 % biodegradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60% biodegradation must be attained within 10 days of the biodegradation exceeding 10 %. The test item can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No. 301B.
- The toxicity control attained 63 % biodegradation after 14 days and 81 % biodegradation after 28 days thereby confirming that the test item did not exhibit an inhibitory effect on the sewage treatment micro-organisms used in the test.
Results with reference substance:
- Sodium benzoate attained 71 % biodegradation after 14 days and 76 % biodegradation after 28 days thereby confirming the suitability of the inoculum and test conditions.
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test item attained 73 % biodegradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60 % biodegradation must be attained within 10 days of the biodegradation exceeding 10 %. The test item can therefore be considered to be readilybiodegradable under the strict terms and conditions of OECD Guideline No. 301B.
Executive summary:

GUIDELINE

A study was performed to assess the ready biodegradability of the test item in an aerobic aqueous medium. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (1992) No. 301B, "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4-C of Commission Regulation (EC) No. 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OCSPP 835.3110 (Paragraph (m)).

 

METHODS

The test item, at a concentration of 10 mg carbon/L, was exposed to activated sewage sludge micro-organisms with mineral medium in sealed culture vessels in the dark at temperatures of between 22 and 24 °C for 28 days. 

 

Following the recommendations of the International Standards Organisation (ISO 10634, (1995)), the test item was dissolved in an auxiliary solvent prior to being adsorbed onto a filter paper and subsequent dispersal in test media. Using this method, the test item is evenly distributed throughout the test medium and the surface area of test item exposed to the test organisms is increased thereby increasing the potential for biodegradation.

 

The biodegradation of the test item was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the reference item, sodium benzoate, together with a toxicity control were used for validation purposes.

 

RESULTS

The test item attained 73 % biodegradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60 % biodegradation must be attained within 10 days of the biodegradation exceeding 10 %. The test item can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No. 301B.

Description of key information

The test item attained 73 % biodegradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60 % biodegradation must be attained within 10 days of the biodegradation exceeding 10 %. The test item can therefore be considered to be readily biodegradable (OECD 301 B, EU Method C.4 -C and OCSPP 835.3110).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

GUIDELINE

A study was performed to assess the ready biodegradability of the test item in an aerobic aqueous medium. The method followed was designed to be compatible with the OECD Guidelines for Testing of Chemicals (1992) No. 301B, "Ready Biodegradability; CO2 Evolution Test" referenced as Method C.4-C of Commission Regulation (EC) No. 440/2008 and US EPA Fate, Transport, and Transformation Test Guidelines OCSPP 835.3110 (Paragraph (m)).

 

METHODS

The test item, at a concentration of 10 mg carbon/L, was exposed to activated sewage sludge micro-organisms with mineral medium in sealed culture vessels in the dark at temperatures of between 22 and 24 °C for 28 days. 

 

Following the recommendations of the International Standards Organisation (ISO 10634, (1995)), the test item was dissolved in an auxiliary solvent prior to being adsorbed onto a filter paper and subsequent dispersal in test media. Using this method, the test item is evenly distributed throughout the test medium and the surface area of test item exposed to the test organisms is increased thereby increasing the potential for biodegradation.

 

The biodegradation of the test item was assessed by the determination of carbon dioxide produced. Control solutions with inoculum and the reference item, sodium benzoate, together with a toxicity control were used for validation purposes.

 

RESULTS

The test item attained 73 % biodegradation after 28 days and satisfied the 10-Day window validation criterion, whereby 60 % biodegradation must be attained within 10 days of the biodegradation exceeding 10 %. The test item can therefore be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No. 301B.