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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

In conclusion, chloroform biodegradation is observed in anaerobic sediment. The corresponding half-life of 14 days will be considered here. The TGD proposes that 90 % of the sediment is anaerobic and suggests when only data is available for the anaerobic part correcting the half-life value in order to take into consideration the aerobic fraction of the sediment compartment. Therefore, taking into account the aerobic part of the sediment, only 45 % of the chloroform is biodegraded in 14 days and the actual half-life in the entire sediment is approximately 15 days. This value of 15 days will be used in the assessment for the sediment.

Key value for chemical safety assessment

Half-life in freshwater sediment:
14 d
at the temperature of:
283 K

Additional information

The anaerobic primary degradation of chloroform was studied by Gosset (1985) in batch studies with an inoculum based on municipal digested sludge at 35 °C. At a concentration of 5.1 mg/L, chloroform disappeared within 9 days. The main metabolite was dichloromethane (31%), which remained near constant for 21 days and then disappeared slowly over the remaining 60 days. The quantity of CH4 produced was negligible. Even at 1.7 mg/L, the gas production by the inoculum was inhibited by more than 60%, and by more than 80% at 17 mg/L. Bouwer et al. (1981) carried out a study on the degradation of chloroform with methanogenic bacteria over 112 days. At an initial concentration of 16 μg/L, 81 % of chloroform was degraded within two weeks. Degradation also occurred with initial concentrations of 34 μg/L (> 70% after 28 days) and 157 μg/L (43 % after 84 days). Degradation at the high concentration of 157 μg/L was less conclusive, but there appears to have been a gradual reduction in chloroform concentration. Removal percentages vary in an important way, as they are based on variable CHCl3 measurements in controls. Bouwer and McCarty (1983) found that in seeded cultures under methanogenic conditions, chloroform was almost completely oxidised to CO2. At initial concentrations of 15 and 40 μg/L a lag period of 40 and 20 days was observed respectively. 14C-measurements confirmed the removal by bio-oxidation. Rhee and Speece (1992) carried out a study with methanogenic bacteria under optimised conditions in a continuous fed anaerobic reactor. The feed contained a primary substrate (either formate, acetate or propionate) so as to maintain a concentration of 2000 mg/L of substrate in the reactor. The concentration of CHCl3 in the influent feed solution were 304, 1230 and 1960 mg/L in formate, acetate and proprionate enrichment cultures, respectively. The feed concentrations were chosen to produce a 50 % reduction in gas production. A degradation of 90, 89 and 93 % after 30 days of continuous operation was observed. The concentrations were monitored in the liquid and gas effluent. The removal by volatilisation was 6.2 - 10 % whereas the removal with the liquid effluent was < 0.08 %, corresponding to concentrations of <0.24, <0.98, <1.57 mg/L. Fathepure and Vogel (1991) determined a total decomposition of 83 % after two days in a sequential decomposition process in an anaerobic and aerobic column. A pre-adaptation of 4-6 weeks took place; the aerobic column was working for one year.

Mineralisation of chloroform mainly to CO2 was observed in a test carried out under anaerobic conditions and using muddy, methanogenic sediments (van Beelen and van Vlaardingen 1993). Half-lives between 2 and 37 days were observed at 20 °C. Mineralisation was also found at lower temperatures (10 °C). No mineralisation occurred in sandy sediment samples, which contained similar amounts of bacteria as the muddy sediments. The presence of organic matter in the muddy sediments seemed to be one important factor driving the mineralisation of chloroform. Another study testing the mineralisation of chloroform with methanogenic sediment samples at 10 °C or 20 °C (van Beelen and van Keulen 1990) came to the same conclusion, that chloroform is mineralised under anaerobic conditions resulting in the production of mainly CO2. The half-lives found in these tests were 10 -14 days at 10 °C and 2.6 days at 20 °C.

In conclusion, mineralisation of chloroform is likely to take place under environmental conditions in the anaerobic part of sediments with half-lives in the range of approximately 15 days. The most important degradation product is CO2. However, because no mineralisation occurred in the sandy sediment samples, it can be expected that chloroform may pass the sandy sediments of infiltrating rivers, thus polluting the groundwater.