11-oxahexadecan-16-olide

Biodegradation in water: screening tests

Administrative data

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

The study was conducted between 25 September 1992 and 23 October 1992.

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Data source

Reference

Reference Type:

study report

Title:

Unnamed

Year:

1993

Report date:

1993

Materials and methods

Test guideline

Qualifier:

according to guideline

Guideline:

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

Deviations:

no

GLP compliance:

yes

Test material

Test material information

Constituent 1

Reference substance name:

11-oxahexadecan-16-olide

EC Number:

222-225-5

EC Name:

11-oxahexadecan-16-olide

Cas Number:

3391-83-1

Molecular formula:

C15H28O3

IUPAC Name:

1,7-dioxacycloheptadecan-8-one

Test material form:

liquid

Study design

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge (adaptation not specified)

Details on inoculum:

Secondary effluent from an unacclimatised activated sludge plant at URL North.

Duration of test (contact time):

28 d

Details on study design:

The test used was based on the sealed vessel test which is suitable for determining the ready and ultimate biodegradability of organic substances. The test is conducted in 160 mL vessels (hypovials) containing 100 mL mineral salts medium inoculated with secondary effluent and the respective test or reference substance. Multiple vessels are prepared per substance, sealed with a butyl rubber septum and an aluminium crimp seal. The headspace in each vessel has a volume of 60 mL and, when filled with air, contains approximately 6 times the mass of oxygen required for the complete oxidation of the substance.

The sealed vessels are incubated at 20 °C on a rotary shaker. At intervals during the 28 day test period a vessel is removed and concentration of carbon dioxide in the headspace gas is determined. The seal is then broken and the concentration of inorganic carbon in the test medium is also determined. The total inorganic carbon in the vessel is calculated and corrected by subtracting the total inorganic carbon produced in a control. The control vessels are identical to the test vessels except for the omission of the test substance. From a knowledge of the initial organic carbon concentration added as test substance, the extent of mineralisation can be determined.

The test substances were added directly to the appropriate vessels with a high quality liquid delivery syringe. The volume added (1 – 2 µL) is negligible compared to the total volume of 100 mL in each vessel and is not taken into consideration when determining the results. Analysis of both the headspace gas and the liquid medium for CO2 / DIC was performed after 3, 7, 11, 14, 17, 24 and 28 days using an Ionics 555 Inorganic Carbon Analyser.

Determination of percentage biodegradation
In determining the percentage biodegradation of a test (or reference) substance it is necessary to account for any biodegradation of material in the control. Therefore the percentage biodegradation is given by:
(TICt – TICc) / TC x 100
WhereL
TICt = µg Total Inorganic Carbon in test bottle.
TICc = µg Total Inorganic Carbon in control bottle.
UC = µg organic carbon added to test vessel as test compound.

The Total Inorganic Carbon is the summation of the results of the analysis of the liquid and gas phases of each bottle after reference to the appropriate inorganic carbon standard curve.

On the final day of the study more than one vessel is analysed for both the test compound and the control. In this case, TICc is the arithmetic mean mass of inorganic carbon in the control vessels. The percentage biodegradation is calculated for each individual test vessel and the mean percentage biodegradation and standard deviation are determined and the results expressed as:
Mean % biodegradation ± S.t / √n
Where:
S is the standard deviation
t is the “t” value (two tailed test) at n-1 degrees of freedom at the 0.05 significance level
n is the number of results used to obtain the standard deviation.

Results and discussion

% Degradation

Parameter:

% degradation (CO2 evolution)

Value:

79.6

Sampling time:

28 d

Details on results:

The air temperature during the 28 day test period was in the range of 19 – 21.5 °C. The percentage biodegradation (nominal) of the test substance was 79.6 %.

It should be noted that the percentage biodegration figures are based on nominal carbon concentrations. Consequently for these substances the actual percentage biodegration values will be slightly different depending on the respective purity of the test substance and the identity and organic carbon content of any impurities. However from an examination of the results and given the stated impurties the classification of the test substances according to the test criteria should not be affected.

Benzyl alcohol was selected as the reference substance because it has previously been shown to be readily biodegradable in the Sealed Vessel Test system. Benzyl alcohol achieved 96.3% biodegration after 28 days and the 60% "pass" level was reached within 10 days of exceeding the 10% level. Consequently benzyl alcohol can be classified as readily biodegradable thereby confirming the suitability of the inoculum and the culture conditions of this study.

Applicant's summary and conclusion

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test substance exceeded the 60% pass level and met the 10 day window criterium and hence may be classified as readily biodegradable.

Executive summary:

The test substance exceeded the 60% pass level and met the 10 day window criterium and hence may be classified as readily biodegradable.