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Biodegradation in water: screening tests

Description of key information

OECD Guideline 301D, EU Method C.4-E, US EPA OPPTS 835.3110, GLP, key study, validity 2:
43% degradation after 28 days.
Not readily biodegradable.

Additional information

One key study is available to assess the ready biodegradability of the substance in an aerobic aqueous medium. This study was performed according to OECD Guideline 301D, EU Method C.4 -E and US EPA OPPTS 835.3110.

The substance, at a concentration of 1.5 mg/l, was exposed to sewage treatment micro-organisms with culture medium in sealed culture vessels in the dark at 20 ± 1°C for 28 days.

The following test preparations were prepared and inoculated in 250-300 ml BOD bottles:

a) A control, in duplicate, consisting of inoculated culture medium.

b) The standard material (sodium benzoate), in duplicate, in inoculated culture medium to give a concentration of 3 mg/l.

c) The test material, in duplicate, in inoculated culture medium to give a concentration of 1.5 mg/l.

d) The test material (1.5 mg/l) plus the standard material (1.5 mg/l), in duplicate, in inoculated culture medium to act as a toxicity control.

The oxygen depletion of the inoculated control did not exceed 1.5 mg O2/l after 28 days, the residual oxygen concentration in the test bottles remained at 3.85 mg O2/l or greater in all test vessels and the difference between the extremes of replicate oxygen depletion values at the end of the test was less than 20% in all vessels thereby satisfying the validation criteria. Examination of the degradation curve for the toxicity control showed that the toxicity control attained in excess of 25% degradation by Day 14 of the study thereby confirming that the test material was not toxic to the sewage treatment micro-organisms used in the study. After 28 days the toxicity control had attained 52% degradation. The standard material, sodium benzoate, attained 86% degradation after 28 days thereby confirming the suitability of the test method and culture conditions.

The test material attained 43% degradation after 28 days and therefore cannot be considered to be readily biodegradable under the strict terms and conditions of OECD Guideline No 301D.