2-Methylpropene, trimers

Biodegradation in water: screening tests

Description of key information

A C12 member of this category was shown to be readily biodegradable as 93.9% was degraded after 28 days. Experimental data on C8 and C16 members of this category show these streams to be not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

GLP, guideline studies are available for 3 category members with different carbon numbers: hydrocarbons, C4, 1,3-butadiene-free, polymd., dibutylene fraction (C8), tributene (C12), and hydrocarbons, C4, 1,3-butadiene-free, polymd., tetraisobutylene fraction, hydrogenated (C16). The measured data are supported QSAR estimates for these carbon chain lengths. The butylene oligomers consist predominantly of C8 - C16 carbon chain lengths and so data for these structures are most reflective of the category.

In a GLP, guideline study with hydrocarbons, C4, 1,3-butadiene-free, polymd., dibutylene fraction (C8), 3% biodegradation after 28 days was observed based on the oxygen consumption and therefore hydrocarbons, C4, 1,3-butadiene-free, polymd., dibutylene fraction cannot be considered readily biodegradable.

A GLP compliant study (Evonik Oxeno 2009) according to OECD guideline 310 (CO2 in sealed vessels – headspace test) showed dodecene (C12) to be readily biodegradable as 93.9% was degraded after 28 days. Although additional data from a MITI (1986) study indicates that triisobutylene is not readily biodegradable, limited information is available on this study and it is not considered to be reliable.

Hydrocarbons, C4, 1,3-butadiene-free, polymd., tetraisobutylene fraction, hydrogenated (C16) was shown not to be inherently biodegradable in a GLP study according to CONCAWE and OCSPP 835.3215 Guidelines, as 1 % biodegradation based on CO2 production was observed after 56 days.

A screening assessment for the potential persistence of the butylene oligomers was conducted using QSAR estimates of biodegradability predicted by the model Biowin. Representative structures of C8, C12 and C16 olefins were used in the assessment. This carbon range is within the limits of the model and so use of these structures would provide a more reliable assessment for the category. The QSAR predictions indicate some C12 streams would be readily biodegradable but that representative C8 and C16 structures cannot be considered readily biodegradable.

Estimations of half life generated using the BioHCwin predictive model, which has been developed specifically for hydrocarbons, indicates that the half lives of the representative structures for the C8 to C16 olefins would range from 6.56 to 29.57 days respectively. Based on these predicted half lives the members of the category would not meet the criteria for persistent (P) or very persistent (vP). As the BioHCwin is specifically intended for hydrocarbons and considers a fragment based approach to estimate the biodegradation of larger hydrocarbons, this model will give a more appropriate predication for biodegradation for the butylene oligomers.

Although the hydrocarbon specific QSAR estimates that none of the buytlene oligomers would be persistent in the environment, as reliable measured data are available for three representative structures, the experimental data will be used in the risk assessment. Therefore, the C8 and C16 streams are considered to be not readily biodegradable, while the C12 streams are considered to be readily biodegradable.