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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

22% (28 days), 62% (70 days) (unacclimated)
51% (28 days), 64% (75 days) (acclimated)

Key value for chemical safety assessment

Additional information

No data are available on the biodegradation of isoheptane. Based on a category approach data are read-across to hydrocarbons, C7-C9, isoalkanes. A study is available using a standard OECD 301F manometric respirometry test procedure for this multi-constituent isoalkane substance (Exxon 1998). This study is sufficient to characterize other substances of this sub-category within the C7-C9 hydrocarbon solvents category. The data show that members are not readily biodegradable, but can demonstrate high extents of biodegradability when test durations are extended. Another chemical in this sub-category, 2,2,4-trimethylpentane (CAS 540-84-1), contains a quaternary structure that is known to impede microbial degradation. Therefore, this substance is also not expected to biodegrade readidly, but demonstrates results that are similar to those determined for the multi-constituent isoparaffin substance, which can contain trimethylpentane isomers among other C7 to C9 isomers. Hydrocarbons, C7-C9, isoalkanes composed predominantly of isooctane isomers demonstrated 22 and 62% biodegradation after 28 and 70 days, respectively. A second study was conducted with this substance that used the acclimated inoculum from the previous study, harvested on day 70 (Exxon 1998).The results showed 51 and 64% biodegradation after 28 and 75 days, respectively.