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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Category members with carbon number ranges from C6-24 are considered readily biodegradable. Category members with carbon numbers above C24 are not considered readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A large number of ready biodegradation studies following standard OECD guidelines are available for members of this category. Studies are available for category members with carbon number ranges from C6 to C28. When contradictory results are available from biodegradation screening studies the study which demonstrates the most biodegradation is used in the risk assessment. Therefore, studies demonstrating ready biodegradation have been assigned key study status, in preference to those showing lower rates of degradation. Data has been read across between category members and used to determine the carbon number above which ready biodegradation has not been demonstrated.

Hex-1-ene has been found to be readily biodegradable in a standard biodegradation screening study (MITI, 1989). The biodegradation of the test substance was determined by measuring the oxygen consumption, Total Organic Carbon and concentration of the test substance using GCMS over time. After 28 days >60% biodegradation was observed using each of these measures. The results based on BOD showed a greater than 20% difference between replicates. However, this variability was not observed with the other two measures. Overall, this test demonstrated that hex-1 -ene met the criteria for readily biodegradability. The biodegradation of hex-1 -ene was also investigated by Miller and Watkinson (1985) in a closed bottle test. A maximum of 45% biodegradation was observed, and so the criterion for ready biodegradability was not met in this study.

Decene has been found to be readily biodegradable in a biodegradation screening test (Cidaria, 1995). In this OECD 301F test >80% biodegradation was observed at day 28, and the 10 day window was met.

Olefins with a carbon number range of C10 - 13 have also been found to be readily biodegradable (Turner and Watkinson, 1985). After 28 days 60 -67% biodegradation was observed, indicating that the test substance is readily biodegradable. The same study reports results from a Modified Sturm test which showed 32 -43% biodegradation over 28 days.

Miller and Watkinson (1984) report results from both an OECD 301D and an OECD 301B test with Alkenes C10 - 14. In both cases they found the test item to be readily biodegradable, but failing the ten day window. However, OECD guidance states that the 10 day window is not applicable when testing a mixture of structurally similar chemicals, as here.

Alkenes with a carbon number range of C11 -12 have been found to be readily biodegradable in a biodegradation screening test (Cidaria, 1995). In this OECD 301F test >77% biodegradation was observed at day 28, and the 10 day window was met.

Turner and Watkinson (1985) investigated the biodegradability of tetradec-1 -ene in an OECD 301D closed bottle test. The validity criteria of the test were met, and tetradec-1 -ene was shown to meet the criteria for ready biodegradability.

Battersby (1995) investigated the biodegradability of hexadec-1 -ene in an OECD 301D closed bottle test. The validity criteria of the test were met, and hexadec-1-ene was shown to meet the criteria for ready biodegradability. MITI (1989) report the results of an OECD 301C test with hexadec-1-ene. Biodegradation after 28 days was reported based on BOD or analysed concentrations as 55-77% and 81 -95% respectively. Douglas and Halls (1993) also investigated the biodegradability of hexadec-1-ene in an OECD 301D test. Biodegradation reached a maximum of 31% after 28 days.

Battersby (1995) also reports that C14 -16 alpha olefins was found to be readily biodegradable in an OECD 301D test.

Miller and Watkinson (1984) tested alkenes C15 - 18 in an OECD 301D test. 53 - 66% biodegradation was observed over 28 days. Battersby (1995a) also tested alkenes C15 - 18 in an OECD 301D test and reported 55 - 61% biodegradation over 28 days. In both cases although >60% biodegradation was observed the criteria for ready biodegradability were not met. Miller and Watkinson (1984) also report the results from an OECD 301B study. 39 - 49% biodegradation was measured over 28 days. The study was extended to 41 days, but biodegradation only reached 42 - 52% after this extended period. Taken together, Miller and Watkinson (1984) and Battersby (1995a) indicate that alkenes C15-18 only narrowly miss being considered readily biodegradable.

Miller and Watkinson (1985) investigated the biodegradability of octadec-1 -ene in a test similar to an OECD 301B modified Sturm test and an OECD 301D closed bottle test. The highest level of biodegradation was observed in the modified Sturm test. Although >60% biodegradation was observed within 28 days the 10 -day window criterion was not met. Therefore, despite reaching a high degree of biodegradation octadec-1 -ene was not demonstrated to be readily biodegradable. A maximum of 48% biodegradation was observed in the closed bottle test.

Alkenes with a carbon number range of C20 -24 have been found to be readily biodegradable in a biodegradation screening test (Mead, 1998). After 28 days 92% biodegradation was observed in this modified sturm test. This is supported by another modified Sturm test (Clarke, 2008), where 92% biodegradation was again observed after 28 days. The 10 day window was met in this study therefore the substance is considered readily biodegradable.

These studies demonstrate that C6, C10, C10-13, C10-14, C11-12, C14, C14-16, C16 and C20-24 alkenes have been shown to be readily biodegradable. Alkenes with carbon numbers of C15-18 and C18 have been shown to have >60% degradation within 28 days, but did not meet all the criteria to be considered readily biodegradable. Based on these results any category members with carbon number ranges from C6-24 are considered readily biodegradable. Category members with carbon numbers above C24 are not considered readily biodegradable.

A number of studies are also available showing lower levels of biodegradation for alkenes in the same carbon number ranges, and at higher carbon number ranges. Due to the variability in results from ready biodegradation studies, when a study is available demonstrating ready biodegradation this is reported as the key study. All reliable results are included in the dossier and the table of results for completeness.