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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The registered substance is expected to not be biodegradable based on a weight of evidence provided on four structural analogues.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The biodegradation of the registered substance, 2,2'-methylenebis(6-nonyl-p-cresol), has been addressed using a weight of evidence approach using data on several structural analogues. Read across to the three substances listed below is considered appropriate based on their structural similarities to the registered substance.

 

2,6-di-tert-butyl-p-cresol (CAS No. 128-37-0)

Inui (1979) determined the ready biodegradability of the test material in a study conducted broadly in accordance with the CO2 evolution test outlined as OECD guideline 301 B. The study was performed to sound scientific principles with a sufficient level of detail; accordingly the study was assigned a reliability score of 2 in line with the principles for assessing data quality as defined by Klimisch (1997). Two radiolabelled compounds were utilised and the test material was assessed at several concentrations, together with different concentrations of activated sludge, both with and without ethanol. The test material was biodegraded by activated sludge with evolution of radioactive CO2, evidencing a half life of 3 - 7 days (26 - 50 % of the applied radiocarbon over 35 - 112 days). The degree of decomposition was dependent upon the test material load, concentrations of the applied test material, concentrations of the applied inoculated activated sludge and the duration of incubation. Under the conditions of this study, the test material was shown to be biodegradable.

Anon. (1978) determined the potential of the test material to undergo biodegradation in accordance with the “Biodegradation Test of Chemical Substances” specified in the “Test Method Relating to New Chemical Substances (Kanpogyo No.5, Yakuhatsu No.615, 49 Kikyoku No.392, July 13, 1974)” and broadly in accordance with the principles of OECD 301 C. The study was conducted in accordance with sound scientific principles with limited reporting, and was thus assigned a reliability score of 2 in accordance with Klimisch (1997). Measurement of O2 consumption showed 4.5 % degradation, whereas the results of quantification by gas chromatography showed degradation of 0.8%. Under the conditions of this study, the test material was shown to not be readily biodegradable.

The two available studies for this read-across substance give conflicting information regarding the biodegradability of the substance. Since both studies were performed to a good standard in accordance with sound scientific principles it is not possible to determine whether the substance is biodegradable or not.

 

6,6'-di-tert-butyl-4,4'-butylidenedi-m-cresol (CAS No. 85-60-9)

Saeger (1980) determined the biodegradation of the test material, assessed as part of a screening study performed on eleven rubber chemical products, using the shake flask carbon dioxide evolution procedure. The study was based upon the ASTM Proposed Standard Practice for the Determination of the Ultimate Biodegradability of Organic Chemicals, Draft No. 3, ASTM E35.24 Subcommittee, Aquatic Biotransformation Task Group, 2/80. The study was conducted to sound scientific principles with limited reporting, and was assigned a reliability score of 2 in line with Klimisch (1997). The test was carried out over 35 days using a medium derived from soil, raw sewage and activated sludge mixed liquor. The inoculum was exposed to the test material in triplicate at 20.7 mg/L under aerobic conditions. At the end of the test, 1 % biodegradation was seen (variability range 0 - 5 %).

Under the conditions of the study, the test material was determined to not be biodegradable.

 

6,6'-di-tert-butyl-4,4'-thiodi-m-cresol (CAS No. 96-69-5)

Saeger (1978) determined the inherent biodegradability of the test material by investigating primary and ultimate degradation. The primary biodegradation of the test material was determined in a semi-continuous activated sludge test (SCAS), whereas the ultimate biodegradation was investigated in a Thompson-Duthie-Sturm procedure. The study was conducted in accordance with generally accepted scientific principles, with incomplete reporting or methodological deficiencies, which do not affect the quality of the relevant results. Accordingly the study was assigned a reliability score of 2 in line with Klimisch (1997). In the SCAS test, a mean biodegradation rate of 11 ± 7 % was obtained at the 3 mg/L feed level during a 13 week test, indicating this material to be resistant to biodegradation. In the Thompson-Duthie-Sturm procedure, no CO2 was evolved indicating that no biodegradation took place.

Under the conditions of this study, the test material was determined to not be inherently biodegradable.

 

Conclusion

The overall consensus of the available data is that the registered substance is expected not to biodegrade in the environment.