Purine-2(3H),6(1H)-dione

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)

GLP compliance:

yes

Specific details on test material used for the study:

Purity: 99.9%

Inoculum or test system:

activated sludge, adapted

Details on study design:

TEST CONDITIONS
- Composition of medium: modified biochemical oxygen demand (BOD) test dilution water
- Test temperature: 22 ± 2ºC

TEST SYSTEM
- Culturing apparatus: test chambers were amber 4-liter bottles.
- Number of culture flasks/concentration: test contained blank control group, reference group, a treatment group and a single toxicity control; each group contained three replicate test chambers; treatment group test chambers used to evaluate test substance at nominal concentration of approximately 10 mg C/L; toxicity control was used to evaluate inhibition of test substance to inoculum and was dosed with both reference (10 mg C/L) and test substances (10 mg C/L).

TEST INOCULUM
- Activated sludge: Easton Wastewater Treatment Facility, Easton, Maryland
- Details: Sludge sieved using a 2-mm screen, adjusted to approximately 1000 mg total suspended solids (TSS)/L with mineral media then aerated at test temperature until use; total suspended solids measurement and standard agar plate count performed on inoculum on day of test chamber preparation.
- Plates: incubated at 22 ± 3ºC for approximately 48 hours.

CONTROL AND BLANK SYSTEM
- Inoculum blank: used to measure background CO2 production of inoculum and not dosed with a carbon source.
- Toxicity control: Sodium benzoate (10 mg C/L)

SAMPLING
- Sampling frequency: On days 3, 5, 8, 13, 18, 25, and 29, CO2 trap nearest test chamber was removed and analyzed for inorganic carbon. Except for Day 29, two remaining traps placed one position closer to test chamber and new trap placed on end of series.

Key result

Parameter:

% degradation (CO2 evolution)

Value:

>= 60

Sampling time:

28 d

Details on results:

Evidence of ready biodegradability in Carbon Dioxide Evolution Test was > 60% TCO2 within 28-day test period. In addition, pass level was reached within 10 days of achieving 10% TCO2. Final mean percent biodegradation was 101.6%. Test substance was considered readily biodegradable since more than 60% TCO2 was achieved within 10 days. The toxicity control achieved > 25% degradation by Day 14 and was considered non-inhibitory at the concentration tested in this study.

Results with reference substance:

The toxicity control achieved > 25% degradation by Day 14 and is considered non-inhibitory at the concentration tested in this study.

Validity criteria fulfilled:

yes

Interpretation of results:

readily biodegradable

Conclusions:

The test substance is readily biodegradable.

Executive summary:

The biodegradability of the test material was determined by the Carbon Dioxide Evolution Test Method (OECD Guideline 301B).  In the CO2 test, inoculated mineral medium was dosed with a known amount of test substance as the nominal sole source of organic carbon and aerated with CO2-free air.  The CO2 produced from the mineralization of organic carbon within the test chambers was displaced by the flow of CO2-free air and trapped as K2CO3 in KOH trapping solution.  The amount of CO2 produced by the test substance (corrected for that evolved by the blank inoculum) is expressed as a percentage of the theoretical amount of CO2 (TCO2) that could have been produced if complete biodegradation of the test substance occurred.  The test contained a blank control group, a reference group, a treatment group and a single toxicity control.  Each group contained three replicate test chambers.  The blank control was used to measure the background CO2 production of the inoculum and was not dosed with a carbon source.  The reference chambers were dosed with sodium benzoate, a substance known to be biodegradable, at a nominal concentration of 10 mg C/L.  The treatment group test chambers were used to evaluate the test substance at a nominal concentration of approximately 10 mg C/L.  The toxicity control was used to evaluate the inhibition of the test substance to the inoculum and was dosed with both the reference (10 mg C/L) and test substances (10 mg C/L). The results indicate that the activated sludge inoculum was active, degrading the reference substance an average of 103.8% by the end of the test and that the test substance was not inhibitory to the inoculum at the concentration tested, as the toxicity control exceeded 25% degradation by Day 14 of the study.  The average cumulative percent degradation for the test substance was 101.6% by end of the test. The test material met or exceeded the OECD criteria for ready biodegradability 60% of TCO2 within a 10-day window of reaching 10% TCO2).

Description of key information

Readily biodegradable since more than 60% TCO2 was achieved within 10 days.

Key value for chemical safety assessment

Biodegradation in water:

readily biodegradable

Type of water:

freshwater