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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The ready biodegradability of OTNE (Iso E Super) was determined in a 28-day oxygen consumption test (OECD 301 F), following GLP, using activated sludge from a domestic wastewater treatment plant as the source of the microbial inoculum. The initial concentration of the test substance in the test vessels was 18.8 mg/L (ThOD: 56.4 mg O2/L). The microbial inoculum concentration (mixed liquor suspended solids) SS was 30.0 mg/L. During the test, the temperature was kept at 21.3-22.7°C. The pH value of the content in the test container was maintained between 7.14 and 7.67. The average total oxygen uptake in the inoculum blank was 21.1 mg O2/L at the end of the study, within the normal range of 20-30 mg O2/L. Biodegradation of the reference substance, sodium benzoate, reached 94.9% at 14 days (> 60%). The maximum difference of parallel degradation rate of test substance was 6.40% (< 20%) during the study. Biodegradation of inhibition control was 71.2% at 14 days (> 25%), and the oxygen consumption by test substance was greater than 60% of inoculum blank during the test period indicating that there was no inhibition effect to inoculum. Thus, the test was considered valid. Under the valid conditions, biodegradation of the test substance was 96.3% at the end of the 28-day study, biodegradation was greater than 60% within the 10-day window.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Besides this key study, another ready biodegradability test according to OECD TG 301F is available. The concentration tested was 100 mg/L OTNE (ThOD: 300 mg O2/L), with an activated sludge concentration of 30 mg/l. Under the conditions of the test, OTNE undergoes no biodegradation, even after 42 days. Thus, OTNE should be regarded as not readily biodegradable according to this test (Rudio, 1995a).

Also, the biodegradability of OTNE was tested in a Modified MITI test (OECD TG 301C). The validity criteria for the test were met. The concentration of the test substance added was 100 mg/l, with an activated sludge concentration of 30 mg/l suspended solids. The mean percentage biodegradation found was 0% based on BOD and 11% based on analysed test material concentration. In conclusion, OTNE was not readily biodegradable under the conditions of this test.

Finally, inherent biodegradability of OTNE was determined by the Modified MITI Test (II) according to the OECD Guidelines for Testing of Chemicals, Method No. 302 C. The concentration tested was 30 mg/L OTNE, with an activated sludge concentration of 100 mg/L. OTNE undergoes no biodegradation and should be regarded as not inherently biodegradable according to this test (Rudio, 1995b).