Propane-1,3-diol

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

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)

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

other: secondary activated sludge from a publicly owned treatment works (POTW)

Duration of test (contact time):

28 d

Initial conc.:

42.2 mg/L

Based on:

other: 42.2 mg/L of test substance is added to an inorganic medium providing 20 mg C per liter.

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: mineral media was prepared from stock solutions of appropriate concentrations of mineral components, potassium and sodium sulfates plus ammonium chloride, calcium chloride, magnesium sulfate, and iron (III) chloride.
- Test temperature: Room temperature
- pH: 7.52-7.81
- pH adjusted: no
- Continuous darkness: no. Diffused overhead lighting conditions (or in the dark when the lab was not in use)
- Other: Solutions were stirred continuously using stir bars and plates.

No test vehicle was used. The test and control substances were added directly to the test solutions. Control substance used was sodium benzoate. An inoculum control blank was also prepared as well as a toxicity control. The toxicity control was mineral medium with inoculum and an equal number of test substance and control substance used in the test substance and control substance treatments, respectively. Initial amount of test substance was 42.2 mg/L. Initial amount of control substance was 34.3 mg/L.

TEST SYSTEM
- Culturing apparatus: Four liter experimental glass vials were used as the test vessels
- Method used to create aerobic conditions: Deionized water, mineral media solution and inoculum mixture was aerated with CO2-free air for 3 days to purge the system of carbon dioxide.
- Details of trap for CO2 and volatile organics if used: After the aeration period, three CO2 gas diffusion bottles were filled with Ba(OH)2 solution and connected in series to the exit line of each 4 L flask. The CO2 produced in each test vessel reacted with the barium hydroxide in the diffusion bottles, where it precipitated as barium carbonate. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with HCl. On the day of CO2 measurement, the CO2 absorption bottle closest to the 4L experimental flask was removed for titration. The volume of Ba(OH)2 solution in the CO2 adsorption bottle was measured and transferred to a 250 mL flask. The BA(OH)2 was then titrated with HCl using phenolphthalein as an indicator using a stir bar and magnetic stirrer. The titration was complete when the solution became colorless. On the 28th day, the pH of each test vessel was measured and recorded. Then 1 mL of concentrated HCl was added to each of the test vessels, which were aerated overnight to remove the CO2 present in the test suspensions. On day 29, the last analysis of evolved carbon dioxide was made.

Parameters Observed: The amount of CO2 produced by the test substance during the test was measured and expressed as percent of the theoretical CO2 it should have produced (ThCO2) calculated from the carbon content of the test compound. Biodegradability was therefore expressed as % ThCO2.

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

71

Sampling time:

28 d

Remarks on result:

other: Tested at 42.2 mg/L

Details on results:

ThCO2 was calculated to be 1.73 for 1,3-propanediol mg CO2/mg substance and 2.14 mg CO2/mg substance for sodium benzoate.

1,3-propanediol reached a peak of 71% biodegradability by day 28. Since biodegradability was greater than 60% within 10 days after reaching 10% biodegradation, this chemical is “Readily Biodegradable”. Sodium benzoate (control substance) was greater than 60%, biodegradability within 4 days confirming that the inoculum was viable; therefore the test was valid. In the toxicity control, which includes both the test substance and control substance in the same flask, the substances yielded > 25% biodegradation within 2 days. Therefore, 1,3-propanediol was not inhibitory to microorganisms in the inoculum.

The lag phase of the test substance lasted from day 0 to days 2-3 when an average of 10% biodegradation was attained. The degradation phase of the test substance occurred from about days 2-3 until biodegradation began to reach a plateau on about day 10. The pH of the test solutions of the test and control substances and the inoculum blank at the end of the testing varied by less than 0.5 pH units from the pH of the test solution at day 0.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test substance was readily biodegradable (71% after 28 days).

Executive summary:

The results of the CO2 evolution test indicated that 1,3-propanediol was "readily biodegradable". 1,3-Propanediol reached 10% of the ThCO2 by approximately day 2-3 of testing and surpassed the 60% pass criteria by day 10. The pass level for ready biodegradability is 60% of the ThCO2 production. This pass level was reached in a 10-day window by day 10. The 10-day window began by day 2-3 when the degree of biodegradation had reached 10% ThCO2. Degradation was 71% after 28 days. 1,3-Propanediol was not inhibitory to microorganisms in the inoculum.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Additional information

The test substance was shown to be ready degradable in an OECD 301B study. The amount of carbon dioxide evolution was 71% after 28 days, indicating that the test substance is completely mineralized without any significant metabolites or degradation products. Persistence of the test substance in the environment is therefore not expected.