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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

At the end of the 35-day test period, the activated sludge inoculum was active, degrading the reference substance 94.1 % and, as a UVCB, the test item may be considered rapidly biodegradable since the pass level of 60% of ThIC was achieved within 28 days (OECD 310).

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Key study

Test Guideline

OECD Guideline 310

Method and materials

In the Headspace Test, inoculated test medium was dosed with a known amount of test substance as the nominal sole source of organic carbon and sealed. CO2 evolution from the ultimate aerobic biodegradation of the test substance is determined by measuring the inorganic carbon (IC) produced in the test bottles over that produced in the blank control bottles. The amount of IC produced by the test substance (corrected for that evolved by the controls and the amount added by basification, where applicable) is expressed as a percentage of the theoretical amount of IC (ThIC) that could have been produced if complete biodegradation of the test substance occurred. The test contained a control group, a reference group and a treatment group. Each group contained twenty-seven replicate test chambers. The control chambers were used to measure the background IC production of the inoculum medium and were not dosed with a carbon source. The reference chambers were dosed with 1-octanol, a substance known to be biodegradable, at a nominal concentration of 20 mg C/L. The treatment group test chambers were used to evaluate the test item at a nominal concentration of approximately 20 mg C/L.

Results

The results at the end of the 35-day test period indicated that the activated sludge inoculum was active, degrading the reference substance 94.1%.

The average cumulative percent biodegradation for the test item was 73.1%.

Biodegradation ≥ 60% ThIC within a 10-day window of reaching 10% ThIC in this test demonstrates that a test substance is readily biodegradable under aerobic conditions. The average cumulative percent biodegradation for the test item was 73.1%. The test item may not be considered readily biodegradable under aerobic conditions since biodegradation ≥ 60% ThIC was not achieved within a 10-day window of reaching 10% ThIC. However, as a UVCB, the test item may be considered rapidly biodegradable since the pass level of 60% of ThIC was achieved within 28 days.

Conclusion

The test substance is rapidly biodegradable under the conditions of the study.

Supporting study

Test Guidance

This study was conducted by Wildlife International Ltd.

Method and Materials

The study was conducted according to the procedures outlined in the protocol "Ready biodegradability by the carbon dioxide evolution test method". The protocol was based on the procedures specified in the OECD guideline for testing of chemicals, Methods 301B, and EEC Method C.4 -C.

Results

The viability of the inoculum and validity of the test were supported by the results of the reference substance, sodium benzoate, from which 99.3% of theretical CO2 was evolved. An average percent biodegradation of greater than 60% was achieved within 7 days, thereby fulfilling the criteria for a valid test by reaching the pass level by day 14. The average cumulative percent of theoretical carbon dioxide produced by the test substance at 10 mg C/L was 57.0%.

Conclusions

Evidence of ready biodegradability in a carbon dioxide evolution test is 60% TCO2 within the 28 -d test period. In addition, the pass value must be reached within 10 days of achieving 10% TCO2. The test item may not be considered readily biodegradable under the conditions tested since the pass level of 60% TCO2 was not achieved. However since tests of ready biodegradability provide limited opportunity for biodegradation to occur, a negative result does not mean that the test substance will not be biodegraded under relevant environmental conditions.