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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The results of the QSAR predictions for the butenes category (but-1-ene (CAS 106-98-9), 2-butene (CAS 107-01-7) and 2-methylpropene (CAS 115-11-7)) indicate that they are expected to degrade rapidly, with estimated half lives of 2.8 days, 2 day and 2 days for each of the isomers respectively.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

The results of the QSAR predictions for the butenes category (but-1-ene (CAS 106-98-9), 2 -butene (CAS 107-01-7) and 2-methylpropene (CAS 115-11-7)) indicate that they are expected to degrade rapidly, with estimated half lives of 2 days to 2.8 days for the isomers. These results indicate that they would not meet the criteria for persistent in the PBT assessment and do not indicate the potential for long term effects in the environment for the classification and labelling assessment.

As the butenes are gases at standard temperature and pressure, conducting a standard ready biodegradability test is technically difficult and, based on exposure estimates, the test may not be relevant. Therefore, the use of a QSAR to predict the biodegradability of the butenes category members is an appropriate technique to use a part of a weight of evidence approach. The use of BioHCwin v 1.01 (Howard et al. 2005) and Biowin v 4.1 (Howard et al. 1992) is appropriate for the butenes as these compounds clearly fall within the applicability domains of these models as all substructures in butenes category are included in the models. The results from both QSAR models indicate that butenes are expected to biodegrade rapidly.

In addition, various researchers have isolated micro-organisms that are capable of metabolising but-1-ene (e.g. Hou et al. 1983). Although this study does not follow standard guidelines for ready biodegradability tests, it does demonstrate that micro-organisms can biodegrade butenes in aerobic conditions. This review adds to the weight of evidence that members of the butenes category can be expected to biodegrade if released to the environment.