Oxazolidine, 3-butyl-2-(1-ethylpentyl)-

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

from 1997-03-18 to 1997-06-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

comparable to guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Version / remarks:

adopted 17.07.1992

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Version / remarks:

adopted 31.07.1992

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

A sample of activated sludge was collected from one of the return lines at Burley Menston sewage treatment works (Yorkshire Water), a treatment works whose waste-water catchment is predominantly domestic.
On arrival in the laboratory, the sample was aerated by means of a compressed air supply delivered through a diffuser block.
The suspended solids concentration was determined by filtering a 25 mL subsample through a pre-dried and pre-weighed glass microfibre filter (Whatman GF/C). The filter and retained solids were then dried by microwave oven, re-weighed and the contribution made by the sludge solids determined by difference.
The activated sludge inoculum was not acclimatised or adapted to the test item before exposure in this study.

Duration of test (contact time):

28 d

Initial conc.:

>= 20.3 - <= 20.4 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium:
The test was conducted in a synthetic mineral salts medium based on reverse-osmosis water. A medium concentrate was prepared which contained 10 mL/L solution (a) and 1 mL/L of each of solutions (b), (c) and (d) which were composed as follows:
(a) 8.5002 g potassium dihydrogen phosphate (BDH); 21.7515 g dipotassium hydrogen phosphate (Aldrich); 33.4007 g disodium hydrogen phosphate dihydrate (BDH); 0.4997 g ammonium chloride (Sigma), all dissolved in and made up to 1 L in reverse-osmosis water;
(b) 36.4001 g calcium chloride dihydrate (Fisons), dissolved in and made up to 1 L in reverse-osmosis water;
(c) 22.4996 g magnesium sulphate heptahydrate (BDH), dissolved in and made up to 1 L in reverse-osmosis water;
(d) 0.2504 g ferric chloride hexahydrate (Sigma) plus one drop concentrated hydrochloric acid (BDH), dissolved in and made up to 1 L in reverse-osmosis water.

- Test temperature:
The incubation and test measurements were conducted in a facility where the temperature was set at a nominal 21 °C. Temperatures recorded during the study were in the range 21.1 to 23.7 °C, and were therefore compliant with the test Guideline requirement that the temperature be maintained in the range 22 ± 2 °C.

- pH:
Measurements of pH were made at the start of incubation in the blank and reference vessels only. The reason for omitting the vessels which contained the test item was the risk that the pH electrode would become coated with the undissolved test substance to the extent that considerable amounts of the test item might be removed when the electrode was withdrawn to verify the eventual yield of CO2. Final pH readings were made in all vessels on Day 28, immediately before their contents were acidified to release any residual CO2 remaining in solution. The pH measurements recorded at the start and end of the incubation showed that in the blank and reference vessels the pH remained within the range of tolerance of microorganisms likely to be present in the inoculum. Although no initial measurements were made in the vessels containing the test item, the final measurements suggested that the pH remained within the range of tolerance of microorganisms likely to be present in the inoculum. It was therefore unlikely that the course of degradation of the test substance was influenced by adverse pH conditions.

- Aeration of dilution water:
The air flow in this study was regulated in two stages. Initial coarse control was provided by air taps and the air flow to each vessel regulated by individual needle valves. Measurements were made with a bubble flow meter and stop-watch, at intervals not exceeding three days, of the flow rate exiting each test vessel through its train of scrubbers. Adjustments were made as necessary to maintain a flow rate in the range of 50 to 100 mL per minute.
The air used in this study was nominally CO2-free 'control air' (Air Products), fed from cylinders. As an added precaution, the flow passed through a column packed with 'Carbosorb AS' (Merck), a self-indicating, artificial silicate CO2 absorber.

- Suspended solids concentration:
On the basis of the suspended solids determination described above, the medium concentrate was inoculated with activated sludge to provide a nominal solids concentration of 90 mg/L. One litre of medium was added to each test vessel and made up to 3 L by addition of reverse-osmosis water. The final suspended solids concentration in all vessels was thus nominally 30 mg/L.

- Continuous darkness: yes

TEST SYSTEM
- Number of culture flasks/concentration: 2 (duplicates)

SAMPLING
At intervals during incubation, CO2-scrubbers were detached and their contents titrated with acid to determine the quantity of CO2 purged from the respective test vessels. At the end of incubation, the test vessel contents were acidified to release any residual CO2 which remained in solution. After correcting yields for the CO2 generated from a pair of blank vessels containing only inoculated medium, the extent of biodegradation was determined by expressing the cumulative recovered yield as a percentage of the theoretical, calculated from the carbon content of the test substance.


CONTROL AND BLANK SYSTEM
- Toxicity control: 1
- Other: Reference substance: sodium benzoate, dosed in duplicate vessels

Key result

Parameter:

% degradation (CO2 evolution)

Value:

63

Sampling time:

28 d

Details on results:

An initial two day lag was followed by a phase of rapid CO2 generation that continued until Day 8. CO2 generation then slowed to a more gradual rate and continued to the end of the incubation. The final CO2 yields for the test substance, expressed as a percentage of theoretical, were 60 % in one replicate and 66 % in the other. The extent of degradation exceeds the 60 % 'pass' level that conventionally corresponds to complete mineralisation. In relation to the ten day window, for both replicates degradation marginally failed to reach 60 % within ten days counting from the point at which C02 production crossed the 10 % threshold. Divergence between the replicates did not exceed 6 %.

Results with reference substance:

Rapid CO2 generation commenced immediately and declined to a more gradual rate at around Day 8. Final degradation values of 90 and 93 % were recorded in the two replicates, and at no time did degradation in either replicate diverge from that recorded in the other by more than 3 %. Both sodium benzoate replicates reached the 60 % 'pass' level within the ten day window.

Validity criteria fulfilled:

yes

Interpretation of results:

inherently biodegradable, fulfilling specific criteria

Conclusions:

The results obtained in this ready biodegradability assessment showed that the carbon dioxide evolution from the test item reached a mean of 63 % over the course of the 28 day incubation. The CO2 production failed to meet the ten day window requirement and, therefore, the test item cannot be classified as readily biodegradable. Nevertheless, the results of this study show that the test item is inherently biodegradable.

Executive summary:

The ready biodegradability of the test item was assessed by measurement of carbon dioxide (CO2) evolution according to OECD guideline 301 B and EU method C.4-C. Carbon dioxide evolution from the test item reached a mean of 63 % (66 % maximum) at the applied concentration over the course of the 28 day incubation. This exceeds the 60 % level that conventionally represents complete mineralisation. However, CO2 production failed to meet the ten day window requirement and, therefore, the test item cannot be classified as readily biodegradable. Nevertheless, the results of this study show that the test item is inherently biodegradable. The ready biodegradability methods were devised, not as simulations of real aquatic environments, but as stringent fail-safe tests to screen for and to classify substances that would degrade rapidly and completely in natural water bodies. Although the test item has failed to qualify for classification as readily biodegradable under the conditions employed in this study, the extent of mineralisation achieved in 28 days suggests that the substance is unlikely to persist or accumulate in the aerobic environment.

Description of key information

The results obtained in this ready biodegradability assessment showed that the carbon dioxide evolution from the test item reached a mean of 63 % over the course of the 28 day incubation. The CO2 production failed to meet the ten day window requirement and, therefore, the test item cannot be classified as readily biodegradable. Nevertheless, the results of this study show that the test item is inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

inherently biodegradable, fulfilling specific criteria

Type of water:

freshwater

Additional information

The ready biodegradability of the test item was assessed by measurement of carbon dioxide (CO2) evolution according to OECD guideline 301 B and EU method C.4-C. Carbon dioxide evolution from the test item reached a mean of 63 % (66 % maximum) at the applied concentration over the course of the 28 day incubation. This exceeds the 60 % level that conventionally represents complete mineralisation. However, CO2 production failed to meet the ten day window requirement and, therefore, the test item cannot be classified as readily biodegradable. Nevertheless, the results of this study show that the test item is inherently biodegradable. The ready biodegradability methods were devised, not as simulations of real aquatic environments, but as stringent fail-safe tests to screen for and to classify substances that would degrade rapidly and completely in natural water bodies. Although the test item has failed to qualify for classification as readily biodegradable under the conditions employed in this study, the extent of mineralisation achieved in 28 days suggests that the substance is unlikely to persist or accumulate in the aerobic environment.