Hexane-1,2,6-triol

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:

2017-01-31 to 2017-06-09

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Specific details on test material used for the study:

Theoretical Oxygen Demand ThOD NH4: 1.908 mg oxygen per mg test item

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): sewage treatment plant in Bensheim, Germany
- Method of cultivation: aerobic activated sludge was washed by centrifugation and the supernatant liquid phase was decanted. The solid material was resuspended in test water and centrifuged again. This procedure was done three times. An aliquot of the final sludge suspension was weighed, dried and the ratio of wet sludge to its dry weight was determined.
- Preparation of inoculum for exposure: Calculated aliquots of washed sludge suspension, corresponding to 3.5 g dry material/L were mixed with test water and aerated overnight. The suspension was used for the experiment.
- Test water: Pure water with analytical grade salts
- Concentration of sludge: 3.5 g dry material/L, final sludge concentration in test flask: 28.7 mg sludge/L

The oxygen demand of the inoculum control (medium and inoculum) was 35 mg O2/L and thus not greater than 60 mg O2/L within 28 days as required by the test guideline.

Duration of test (contact time):

28 d

Initial conc.:

195.1 mg/L

Based on:

ThOD

Initial conc.:

102.3 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

O2 consumption

Details on study design:

TEST CONDITIONS
- Composition of medium: reconstituted test water
- Test temperature: 22 °C +/-1 °C
- pH: 7.7 at test start, 7.3 to 7.6 at test end
- pH adjusted: no
- Aeration of dilution water: no
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: test flask with a volume of approx. 500 mL
- Number of culture flasks/concentration: 2
- Measuring equipment: BSB/BOD sensor system to measure changes of the pressure in the test flask

- Details of trap for CO2 : carbon dioxide is absorbed in an aqueous solution of potassium hydroxide (45%)


SAMPLING
- Sampling frequency: daily
- Sampling method: BSB/BOD sensor system

CONTROL AND BLANK SYSTEM
- Inoculum blank: 2
- Abiotic sterile control: 1
- Toxicity control: 1
- Other: procedure control with sodium benzoate

Reference substance:

benzoic acid, sodium salt

Key result

Parameter:

% degradation (O2 consumption)

Value:

68

Sampling time:

28 d

Details on results:

The 10-day windows began on day 8 after application, the mean value was calculated to be 12% biodegradation. Therefore, the end of the 10-day window was day on day 18. After correction for the mean biochemical oxygen demand of the inoculum controls the mean biodegradation percentage based on ThODNH4 at the end of the 10-day window was 62%; the criterion of the 10 day window was passed. The mean biodegradation percentage at the end of the 28-day exposure period was 68%.

In the toxicity control containing both, the test item and the reference item, 59% biodegradation was noted within 14 days and 66% bio-degradation after 28 days of incubation. According to the test guidelines, the test item can be assumed to be not inhibitory to the aerobic activated sludge microorganisms because degradation was >25% within 14 days.
The oxygen demand in the abiotic control was 0 mg/L during the test duration. There was no use to correct the degradation of the test item and toxicity control.

Results with reference substance:

The reference item was degraded to 81% after 14 days and to 81% after 28 days of incubation. The percentage biodegradation of the reference item confirms the suitability of the used aerobic activated sludge inoculum.

Summary of biodegradation results of the test item, the reference item and the toxicity control

	Biodegradation [%]
Time (days)	1,2,6-Hexanetriol	Sodium Benzoate	Toxicity control
8 (start of 10-day window)	12	78	34
14	48	81	59
18 (end of 10-day window)	62	84	65
28	68	81	66

Validity criteria fulfilled:

yes

Remarks:

-oxygen demand of inoculum control; pH value of test item flask at test end; degradation in reference item; degradation in toxicity control; difference of duplicate values for the degra-dation of the test item

Interpretation of results:

readily biodegradable

Conclusions:

The degradation rate of 1,2,6-Hexanetriol reached 60% within the 10-day window and after 28 days. Therefore, 1,2,6-Hexanetriol is considered to be readily biodegradable.

Description of key information

The test substance is readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

Biodegradation of the test substance has been tested in a GLP-compliant test according to the OECD technical guideline 301 F. The degradation rate of 1,2,6-Hexanetriol reached 60% within the 10-day window and after 28 days. Therefore, 1,2,6-Hexanetriol is considered to be readily biodegradable. Further publications demonstrated that the test substance can be oxidized by G. suboxydans.