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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Data are not available to demonstrate that 1,3-butadiene is readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

As 1,3-butadiene is a gas 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. An OECD TG 301D closed bottle test (MITI, 2001) reported 0 - 4% biodegradation over 28 days. We have been unable to obtain a copy of the original report in order to assess its reliability.

In the absence of a standard study the use of a QSAR model to predict the biodegradability of 1,3-butadiene is an appropriate technique to use as part of a weight of evidence approach to fulfil this endpoint requirement. The use of Biowin is appropriate for 1,3-butadiene as this compound falls within the applicability domains of this model. Results from QSAR models are generally used to confirm persistence, rather than to indicate ready biodegradation. The results from the Biowin model do not indicate that 1,3-butadiene would be expected to be persistent.

In addition, various researchers have isolated microorganisms that are capable of metabolising 1,3-butadiene. One group (Houet al., 1983) demonstrated that microorganisms can biodegrade 1,3-butadiene under aerobic conditions, however, the study did not follow a standard test guideline for ready biodegradability. This results add to the weight of evidence that 1,3-butadiene has the potential to biodegrade if released to the environment.

Ready biodegradation of 1,3-butadiene has not been demonstrated and for the purposes of the risk assessment ready biodegradability will not be assumed. This was also the approach followed in the EU RAR for 1,3-butadiene (2002), which concluded that there were insufficient data to determine whether or not 1,3-butadiene would be classed as readily biodegradable. The EU RAR thus assumed that no biodegradation of 1,3-butadiene would occur (a biodegradation rate of 0).