1,6-Hexanolide

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:

November to December 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

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

GLP compliance:

yes

Specific details on test material used for the study:

SOURCE OF TEST MATERIAL
- Source and lot/batch: Solvay S.A., Brussels, Belgium
- Lot/batch no: W A2809/0792
- Purity test date: No data

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Secondary (biological) activated sludge was obtained from an activated sludge plant in the Netherlands treating predominantly domestic waste water (> 85 %). The dry weight of the inoculum appeared to be 4.7 mg/ml.

Duration of test (contact time):

28 d

Initial conc.:

10 mg/L

Based on:

test mat.

Initial conc.:

20 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: FeCl3, MgSO4.7H2O, CaCl2, KH2PO4, K2HPO4, Na2HPO4.2H2O, NH4Cl, and (NH4)2SO4.
- Test temperature: 20 ± 1 °C
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus:
- Number of culture flasks/concentration: Fourteen two-litre glass bottles with a CO2 trap were used in these tests. Each of these bottles was about 0.7 L mineral salt medium and 6.38 ml inoculum. The contents of the flasks were made up to 1000 g (which is 1000 ml water) with mineral salt medium, so the concentration of the inoculum was 30 mg dry weight/I and the concentrations of the test compounds was 100 mg sodium acetate/I (group B), 100 mg sodium acetate and 20 mg e-caprolactone/L (group C), 10 mg e-caprolactone/L (group E) and 20 mg e-caprolactone/L (group F) - table 1.
- Method used to create anaerobic conditions: erated with CO2-free air during 24 hours in the dark at 20 ± 1 °C to purge the system of carbon dioxide
- Details of trap for CO2 and volatile organics if used: The CO2 absorption vials were replaced by fresh ones after 7, 14 and 21 days. The amount of CO2 absorbed was determined by titration with 0.5 M HCI. After 28 days of incubation 5 ml 0.5 M HCl was added to the test flasks for removing CO2 or carbonate dissolved in the medium and a fresh CO2 absorption vial was mounted.
After 24 hours of incubation the amount of CO2 absorbed was determined by titration.

SAMPLING
- Sampling frequency: the pH value of the medium was measured at the start and after 28 days of incubation.

CONTROL AND BLANK SYSTEM
See table 1 for details

STATISTICAL METHODS: The biodegradation was calculated as the ratio of the amount of CO2 produced to the theoretical CO2 content as shown in equation 1.
Equation 1: % biodegradation= (mg CO2 produced/mg ThCO2 added in the test) × 100 %, n which ThCO2 is the theoretical CO2 content.

Reference substance:

other: sodium acetate

Preliminary study:

No results reported.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

105

Sampling time:

28 d

Remarks on result:

other: 10 mg/l e-Caprolactone

Parameter:

% degradation (CO2 evolution)

Value:

76

Sampling time:

14 d

Remarks on result:

other: 10 mg/l e-Caprolactone

Parameter:

% degradation (CO2 evolution)

Value:

47

Sampling time:

14 d

Remarks on result:

other: 20 mg/l e-Caprolactone

Details on results:

- The test compound had no significant influence on the pH.
- The positive control vessel indicated the activity of the inoculum was sufficient, with sodium acetate being degraded at > 60 % within 28 days.
- The total CO2-evolution in the inoculum blank at the end of the test was 21 mg.
- 10 day window: At the concentration of 10 mg/L, the degree of biodegradation of the test material at 7 days was 43 %, and after 14 days 76 %. Due to the sampling schedule used it is difficult to conclude comprehensively whether the 10 day window criteria have been met. However, it is noted that the degree of biodegradation observed for the test material at a concentration of 10 mg/L actually exceeds that observed for the reference material (sodium acetate).

Results with reference substance:

Biodegradation of the reference substance at the concnetration of 100 mg/l was 76 % after 28 days (sodium acetate, 100 mg/l). At the same concentration, the reference substance showed 28 % biodegredation after 28 days with the addition of the test material (20 mg/l).

It is concluded that the test substance can be classified as readily biodegradable at a concentration of 10 mg/L. At a concentration of 20 mg/L, there is clear inhibition of the reference sample by the test substance. The degree of biodegradation of the test substance after 29 days was 56 %, indicating a potential of hexan-6-olide to inhibit microorganisms at higher concentrations.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test material at a concentration of 10 mg/L is readily biodegradable. At a concentration of 20 mg/L, the test material showed inhibitory effects on the inoculum.

Executive summary:

The biodegradation of the test material was determined following OECD test guideline 301B (ready biodegradability, modified Sturm test, 1982). The study is considered reliable (Klimisch 1) and was conducted according to GLP. The test substance can be classified as readily biodegradable at a concentration of 10 mg/L. It was not clear whether the 10 day window was passed due to the timing of the sampling regime. At a concentration of 20 mg/L the test substance was inhibitory to the incoulum.

Description of key information

Hexan-6-olide can be classified as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The biodegradation of the test material was determined following OECD test guideline 301B (ready biodegradability, modified Sturm test, 1982). The test substance can be classified as readily biodegradable at a concentration of 10 mg/L, although it was not clear whether the 10 day window was passed due to the sampling regime. At a concentration of 20 mg/L the test substance was inhibitory to the inoculum.