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Environmental fate & pathways

Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: inherent biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Principles of method if other than guideline:
The ultimate degradation of the rubber chemicals to carbon dioxide was determined using the Monsanto shake flask procedure. The method is similar to ASTM draft method no. 2 ASTM Committee E35.24.
GLP compliance:
not specified
Oxygen conditions:
aerobic
Inoculum or test system:
other: raw sewage, soil, and activated sludge mixture, acclimated
Duration of test (contact time):
35 d
Initial conc.:
20 mg/L
Based on:
test mat.
Initial conc.:
30 mg/L
Based on:
test mat.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
ca. 0
Sampling time:
35 d

Method is similar in principle to Sturm test measuring ultimate biodegradation as CO2 evolved

Interpretation of results:
not inherently biodegradable
Conclusions:
No biodegradation of CBS was observed during 35 days of exposure to acclimated bacterial inoculum (Monsanto, 1979); and hence CBS can be concluded as not inherently biodegradable.
Executive summary:

The inherent biodegradability of the test substance N-cyclohexxylbenzothiazole-2-sulphenamide was assessed in a study according the internal Monsanto shake flask method, which is similar to that deescribed in Draft Method No.2 for the proposed standard for the determination of the ultimate biodegradability of organic chemicals of the ASTM Committee E35.24 (1979). The substance was added to an inoculum of acclimated bacteria, which were previously mixed with a minimal salts media in a fluted 2-liter Erlenmeyer flask, after aerating the mixture with 70% oxygen in nitrogen. The Erlenmeyer flask was connected to a reservoir containing a 0.15 N barium hydroxide solution to trap evolving CO2 following biodegradation. The formation of CO2 was examined by titrating the barium hydroxide solution regularly.


For the test substance no biodegradation was observed during 35 days of exposure to acclimated bacterial inoculum (Monsanto, 1979); and hence N-cyclohexylbenzothiazole-2-sulphenamide can be concluded as not inherently biodegradable.

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study without detailed documentation
Qualifier:
according to guideline
Guideline:
EU Method C.4-F (Determination of the "Ready" Biodegradability - MITI Test)
Version / remarks:
Cited as Directive 84/449/EEC, C.7
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Duration of test (contact time):
28 d
Initial conc.:
100 mg/L
Based on:
test mat.
Reference substance:
aniline
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d

71% aniline was biodegraded in 28 days according to oxygen consumption.

Validity criteria fulfilled:
yes
Remarks:
see 'Additional information'
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
For the test substance N-cyclohexylbenzothiazole-2-sulphenamide no biodegradation under test conditions was observed after 28 days in a guideline study according EU method C. 4.
Executive summary:

In a MITI test according to EU method C. 4 the ready biodegradation of CBS was investigated (Bayer, 1989). After 28 days 0 % degradation of the test substance was determined and hence CBS under test conditions is not biodegradable.

Description of key information

In a MITI test according to EU method C. 4 the ready biodegradation of CBS was investigated (Bayer, 1989). After 28 days 0 % degradation of the test substance was determined and hence CBS under test conditions is not biodegradable. Even with adapted bacterial inoculum CBS was observed to be 0% biodegradable during 35 days incubation (Monsanto, 1979). In the EU-risk assessment, information regarding the biodegardabilities of the main metabolites of CBS, such as MBT, MBTS, BT, BTon, MeSBT and MeBT, is also summarized and discussed. The described metabolites are also not readily biodegradable. Only when the inoculi were adapted under special conditions, certain level of degradation of MBT, BT, BTon, and MeSBT was observed. Such processes are expected in biological treatment plant, but not in the environment.

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

The concentrations (100 mg/l) used in the study of Bayer (1989) are much higher than the water solubility of CBS (i.e. 0.32 mg/l). Although CBS can be rather rapidly hydrolyzed with a half-life of 12.5 hours, the amount of CBS used was sufficient to maintain CBS at saturation level in aqueous phase. As the main hydrolysis product, benzothiazole (BT) has a toxicity to microorganisms (3h-EC50) of 650 mg/l (Yo-shioka et al., 1986). The original concentrations from CBS are not high enough to reach the critical level of BT's toxicity to microorganisms, and hence no inhibition due to hydrolysis products is expected.