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Environmental fate & pathways

Biodegradation in soil

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Description of key information

The available data indicate that chloroform in soil is degraded only under specific conditions by methane-utilising bacteria. It is therefore assumed that chloroform is not bio-degraded in soils.

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Additional information

The following text is copied from the draft EU Risk Assessment Report for chloroform prepared by the French authorities (France 2007), section 3.1.1.5.1.4 (page 50):

"No results from standardised biodegradation systems for soil and sediment are available. In a study performed on a sandy soil (Strand and Shippert, 1986), it was found that acclimation to an air-natural gas mixture stimulated the biological oxidation of chloroform to carbon dioxide. Acclimation of the soil was carried out for 3-8 weeks in an atmosphere of 1 % natural gas in air and around 200 ml of dechlorinated tap water/day constantly applied to the soil during this period. Degradation experiments were carried out using around 5 g of the acclimated soil and a chloroform concentration of 31 μg/kg wet soil. Incubations were performed at 22-25°C for 5 days. Chloroform oxidation continued up to 31 days but was inhibited by acetylene and high concentrations of methane, indicating that methane oxidising bacteria may catalyse chloroform oxidation. There was some chloroform oxidation observed in soils that were exposed only to ambient air (which may have included some hydrocarbons) but the rate in the natural gas enriched soils was four times greater. In conclusion, these results demonstrate that degradation of chloroform occurs only under certain aerobic conditions by methane-utilising bacteria. However, they cannot be used in the generic assessment. The first order rate constant for aerobic biodegradation in soil and sediment is 0 d-1."