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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Data waiving: ”Hydrocarbons C14-C20, aliphatics, ≤2% aromatics”, including the substance Octadecane, have been shown to be readily biodegradable. Therefore, simulation testing on ultimate degradation in soil does not need to be conducted.
Supporting information for demonstrating rapid biodegradation in soil:
- Test material Distillates (Fischer-Tropsch), C8-26 - branched and linear (OECD 307; GLP): Indicative half-life (both biodegradation and physicochemical removal mechanisms) DT50 in biotic system at 1000 mg/kg, of 22.4 days (at 20 ± 2°C) compared to predicted DT50 of 82.6 days in a sterile system (one soil type only).
- Test material Dodecane (OECD 307; GLP): Biodegradation half-life cannot be determined on the basis of this test because of significant losses of test substance during soil preparation; removal from test system dominated by volatilisation. DT50 considered to be < 1 day (at 20 ± 2°C).
- Test material Hexadecane (OECD 307; GLP): Indicative half-life at 32 mg/kg, of 1.5 days (at 20 ± 2°C) in biotic system compared to 32.9 days in a sterile system (in one soil type only). Removal from test system dominated by biodegradation.
- Test material Eicosane (OECD 307, GLP): Indicative half-life at 27 mg/kg, of 11.4 days (at 20 ± 2°C) in biotic system compared to a predicted value of 122 days in a sterile system (one soil type only). Removal from test system dominated by biodegradation.

Key value for chemical safety assessment

Additional information

”Hydrocarbons C14-C20, aliphatics, ≤2% aromatics”, including the substance Octadecane, have been shown to be readily biodegradable. According to Column 2 of Annex IX on the standard information requirements, simulation testing on ultimate degradation in soil does not need to be conducted if the substance is readily biodegradable.

The data waiving is supported by measured data from the closely related substance ‘Distillates (Fischer-Tropsch), C8-26 - branched and linear’ covering the relevant carbon number range of the Category “Hydrocarbons, C14-C20, aliphatics, <2% aromatics”. At this GLP study (OECD 307)three related alkanes (Hexadecane, Eicosane and Dodecane) were applied separately to monitor the rates of degradation of single compounds compared to the test item.

Results:

- Test material Distillates (Fischer-Tropsch), C8-26 - branched and linear: Indicative half-life (both biodegradation and physicochemical removal mechanisms) DT50 in biotic system at 1000 mg/kg, of 22.4 days (at 20 ± 2°C) compared to predicted DT50 of 82.6 days in a sterile system (one soil type only).

- Test material Dodecane: Biodegradation half-life cannot be determined on the basis of this test because of significant losses of test substance during soil preparation; removal from test system dominated by volatilisation. DT50 considered to be < 1 day (at 20 ± 2°C).

- Test material Hexadecane: Indicative half-life at 32 mg/kg, of 1.5 days (at 20 ± 2°C) in biotic system compared to 32.9 days in a sterile system (in one soil type only). Removal from test system dominated by biodegradation.

- Test material Eicosane: Indicative half-life at 27 mg/kg, of 11.4 days (at 20 ± 2°C) in biotic system compared to a predicted value of 122 days in a sterile system (one soil type only). Removal from test system dominated by biodegradation.

It can be concluded that a significant degree of removal, including biodegradation, will occur in soil.