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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

As the member streams within this Category 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 this Category is an appropriate technique for this endpoint.

As the category is made up of C4 hydrocarbons, representative hydrocarbon C4 substances butane (CAS no. 106-97-8), isobutane (CAS No. 75-28-5), isobutene (CAS No. 115 -11 -7) and but-1 -ene (CAS No. 106-98-9) have been used as read-across. Results from all predictions using BIOWIN showed the substances except isobutane to be readily biodegradable. Isobutane, although not readily biodegradable was shown to biodegrade. Therefore streams within this Category are expected to degrade rapidly.

Based on the available data, it is considered that this Category would be classed as readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

But-1-ene, Isobutene and Butane were all shown to be readily biodegradable. Isobutane was deemed not readily biodegradable due to having a Biowin 5 (MITI Linear model) of 0.4898 and Biowin 7 (anaerobic linear) of 0.4315. However Biowin 2 (non-linear model), Biowin 3 (ultimate biodegradation time) and Biowin 6 (MITI non-linear model) were all above the screening criteria for Persistence in the PBTAssessment. In addition, asecond model (BioHCWin v1.01) predicts that isobutene, but-1-ene, isobutane and butane will biodegrade rapidly with a half life of between 1.9 and 3.5 days.