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Biodegradation in water: screening tests

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Biodegradation in water:
under test conditions no biodegradation observed

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The biodegradability of Folenox was investigated in 2 studies. One study evaluated the ready biodegradability of Folenox according to OECD Guideline 301 F (study No. 98-E139). The second study evaluated the inherent biodegradability of Folenox according to a method similar to OECD guideline 302 C (study No. 99-E31).

Ready biodegradability: The readily biodegradability of FOLENOX under the conditions of the Manometric Respirometry Test was investigated according to OECD guideline 301 F and GLP principles. The test substance was tested in duplicate at 100 mg/L. No biodegradation of FOLENOX was observed after 28 days. It was concluded that FOLENOX was not readily biodegradable under the conditions of the Manometric Respirometry Test. The study is deemed acceptable without restrictions.

Inherent biodegradability: The inherent biodegradability of FOLENOX was investigated according to OECD guideline 302 C and GLP principles. The test substance was tested in duplicate at 30 mg/L. No biodegradation of FOLENOX was observed after 33 days. It was concluded that FOLENOX was not inherently biodegradable under the conditions of the Modified MITI Test (II). The study design was a combination of OECD 302 C (i.e. higher sludge/test substance ratio) and OECD 301 F (i.e. sludge collect from 1 site only and test medium). This is acceptable as it corresponds to a worst case scenario to determine the biodegradability of the test substance. Based on the above, the conclusion of the study is deemed acceptable with restrictions.

In both studies, apparent negative biodegradation was observed indicating that the test item might have had an inhibitory effect on the micro-organism despite the fact that the optional toxicity test in the 301F study indicated no toxicity to the micro-organisms. However, a toxicity test which is based on the effect of a test substance on the degradation of a readily biodegradable reference item may be less sensitive than assessing the intrinsic respiration of the inoculum to the test substance alone. Two key issues in using the former method to evaluate the toxicity of a substance to be assessed for biodegradability are described by Reynolds et al (1987). The first is that for easily degradable substrates the initial number of active micro-organisms in the inoculum will not be critical. Even if a large proportion of the inoculum is killed, the remaining organisms will proliferate and degrade the substance, still giving a high degradadation rate with no indication of the toxic effect of the test substance added. The second is that the effect of the test substance on the degradation of a reference substance may not reflect the effects of the test substance on those microorganism species responsible for degrading it.

 

LITERATURE REFERENCE:

Reynolds L., Blok J., de Morsier A., Gerike P., Wellens H., Bontinck, W.J. (1987). Evaluation of the toxicity of substances to be assessed for biodegradability. Chemosphere, 16, 2259.