Hydrocarbons, C5-C7, n-alkanes, isoalkanes, < 5% n-hexane

Biodegradation in water: screening tests

Description of key information

Readily biodegradable: 98% (O2 consumption) in 28 days (OECD 301F) (read-across with hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, <5% n-hexane)
Readily biodegradable: 87% (O2 consumption) in 28 days (OECD 301F) (pentane)
Readily biodegradable: 71.43% (O2 consumption) in 28 days (OECD 301F) (isopentane)
Based on a read-across approach with structural analogue substances, Hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% n-hexane, can be considered readily biodegradable.

Additional information

There are no data available on the biodegradation of hydrocarbons, C5-C6, n-alkanes, isoalkanes, <5% n-hexane. However, there are reliable data available considered suitable for read-across using the analogue approach.

The target substance is a hydrocarbon solvent with carbon numbers in the range of C5 to C6. The main constituents of the mixed solvent consist of about 43% of C6 species and about 57% of C5 species. n-Hexane is only present in concentrations < 5% of the total volume.

Taking into account all available data, animal and human toxicity data as well as environmental fate and effects data show that source substances have a similar (eco-)toxicological and environmental fate properties as the target substance.

Therefore, read-across is performed based on an analogue approach (for details please refer to the analogue justification which is attached in section 13 of the technical dossier).

Three studies conducted with analogue substances provide experimental data:

A OECD 301F manometric respirometry test conducted with hydrocarbons, C6-C7, n-alkanes, isoalkanes, cyclics, < 5% n-hexane by Battersby (1997) is available. The test substance was degraded by 98% after 28 days, and degraded by 83% at the end of the 10-day window. The reference substance was degraded by 104%, therefore the test is valid. The test substance is readily biodegradable and does not inhibit degradation.

A further study is available for pentane. ExxonMobil Chemical (1997) conducted a GLP-compliant study which followed guidelines equivalent to OECD 301F manometric respirometry test. There were some minor deviations in test concentrations from the protocol but these were not considered to influence the integrity of the study, so the study was considered reliable and suitable for use as a key study for this endpoint. The study indicates that n-pentane is readily biodegradable, with 65.5% degradation reached after 13 days, thus fulfilling the 10-day criterion, and 87% degradation reached after 28 days. The test was considered valid as 97% degradation of sodium benzoate occured by Day 14.

In another non-GLP study by ExxonMobil Chemical (1996) with isopentane, which followed guidelines equivalent to OECD guideline 301F manometric respirometry test,71.43% degradation occurredand the isopentane was considered to be readily biodegradable.

Furthermore a QSAR calculation by Howard (2005) is available which predicts that hexane is readily biodegradable.