Buta-1,3-diene

Endpoint summary

Description of key 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.

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 show that it is expected that 1,3 -butadiene is rapidly and potentially readily biodegradable. The results from the Biowin and BioHCwin model do not indicate that 1,3-butadiene would be expected to be persistent.

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, though we have been unable to obtain a copy of the original report in order to assess its reliability. In addition, various researchers have isolated microorganisms that are capable of metabolising 1,3 -butadiene. One group (Hou et 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.

One of the screening criteria for persistence in the PBT assessment is that if a substance is considered to be readily biodegradable the substance is screened as being not P and not vP. EPIWIN predicts rapid volatilisation from water (half life of 45 minutes in a river, 2.9 days in a lake) and degradation of 1,3-butadiene is expected to be rapid once in the atmosphere. According to Atkinson (1985), the atmospheric photodegradation half-life for buta-1,3-diene was estimated as 0.24 days. This value was based on a rate constant derived from a range of experimental results assessed to be valid and the concentration of hydroxyl radicals recommended in the Technical Guidance Document (2003). Taken together these data suggest that 1,3-butadiene will not persist in the environment.

Although measured data are not available, the modelled data indicate that the half life of 1,3-butadiene in water is expected to be much lower than the Annex XIII P criterion of 40 days. Therefore, based on the criteria for persistence stipulated in REACH Annex XIII 1,3-butadiene is not considered to be persistent (P) or very persistent (vP). However we must stress that this is on the basis of a modelled data due to lack of experimental data to fulfil this endpoint requirement.