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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:
30 SEP 2011 - 28 NOV 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
A mixed population of sewage treatment micro-organisms was obtained 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 the filtrate maintained on continuous aeration in a temperature controlled room at approximately 21 °C prior to use.
Duration of test (contact time):
28 d
Initial conc.:
1.5 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Information indicated that the water solubility of the test item was negligible. Therefore pre-study solubility/dispersibility work was performed in order to determine the most suitable method of preparation. Following the results of the pre-study solubility work conducted and recommendations of the International Standards Organisation (ISO 1995), the test item was dissolved in an auxiliary solvent prior to being adsorbed onto a filter paper and subsequent dispersal in inoculated culture 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 following test preparations were prepared and inoculated in 250-300 mL Biological Oxygen Demand (BOD) bottles (darkened glass) with ground glass stoppers:
a) A control, consisting of inoculated culture medium plus a filter paper.
b) The reference item (sodium benzoate), in inoculated culture medium plus a filter paper to give a concentration of 3.0 mg/L.
c) The test item on a filter paper, in inoculated culture medium to give a concentration of 1.5 mg/L.
d) The test item on filter paper (1.5 mg/L) plus the reference item (1.0 mg/L), in inoculated culture medium to act as a toxicity control.

The reference item concentration was reduced to 1.0 mg/L in the toxicity control to prevent complete deoxygenation of the test media occurring.
Test media a-d were inoculated with sewage treatment micro-organisms at a rate of 1 drop of inoculum per litre. The test media were transferred by siphon to BOD bottles, which were firmly stoppered to exclude all air bubbles. Sufficient bottles were prepared to allow a single oxygen determination per bottle with duplicate bottles for each test medium at each sampling occasion. The BOD bottles were incubated in darkness in a temperature controlled water bath at approximately 21 °C. Dissolved oxygen concentrations in duplicate samples from the control, reference and test item series were determined, on Days 0, 3, 5, 7, 11, 14, 18, 21,24 and 28.
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
3
Sampling time:
28 d
Details on results:
The oxygen depletion of the inoculated control did not exceed 1.5 mg O2/L after 28 days, the residual oxygen concentration in the test bottles remained at 3.60 mg O2/L or greater in all test vessels and the difference between the extremes of replicate oxygen depletion values at the end of the test was less than 20 % in all vessels thereby satisfying the validation criteria. The test item attained 3 % degradation after 28 days and therefore cannot be considered as readily biodegradable under the strict terms and conditions of OECD Guideline 301D. The toxicity control attained 26 % degradation after 14 days therefore confirming that the test item was not toxic to the sewage treatment micro-organisms used in the test. The reference item, sodium benzoate, attained 88 % degradation after 14 days and 85 % degradation after 28 days thereby confirming the suitability of the test method and culture conditions. The decrease in degradation between Days 14 and 28 was considered to be due to normal biological variation.
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item attained 3 % degradation after 28 days and therefore cannot be considered as readily biodegradable under the strict terms and conditions of OECD Guideline No 301D.
Executive summary:

A study was performed to assess the ready biodegradability of p-diisopropyl benzene using the Closed Bottle Test (OECD 301D). The test item, at a concentration of 1.5 mg/L, was exposed to sewage treatment micro-organisms with culture medium in sealed culture vessels in the dark at approximately 21 for 28 days. Following the recommendations of the International Standards Organisation (ISO 1995), the test item was dissolved in an auxiliary solvent prior to being adsorbed onto a filter paper and subsequent dispersal in inoculated culture 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 degradation of the test item was assessed by the determination of the amount of oxygen consumed. Control solutions with inoculum and the reference item, sodium benzoate, together with a toxicity control were used for validation purposes. The test item attained 3 % degradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301 D.

Description of key information

An OECD 301D ready biodegradation study is available for p-diisopropylbenzene. The test item attained 3 % degradation after 28 days and therefore cannot be considered as readily biodegradable under the strict terms and conditions of OECD Guideline No 301D.

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

An OECD 301D ready biodegradation study was conducted on p-diisopropylbenze. The results of that study showed only 3 % degradation over 28 days. The substance exhibits a low potential for biodegradation. However, the lack of degradation exhibited in the ready biodegradation study may be affected by the low water solubility of the substance, 0.0405 mg/L.