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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

A number of valid studies on the toxicity of chloroform to microorganisms are available investigating either the inhibition of respiration, ammonium consumption, gas production, or cell multiplication and using activating sludge. The most reliable study found the lowest EC50 value of 0.48 mg/L for the inhibition of ammonium consumption of Nitrosomas bacteria.

Key value for chemical safety assessment

EC50 for microorganisms:
0.48 mg/L

Additional information

In their studies, Bringmann and Kühn (1976 -1980) used the cell multiplication inhibition test to investigate the toxicity of chloroform to the bacteria Pseudomonas putida, the protozoa Entosiphon sulcatum and the flagellate Chilomonas paramaecium. The lowest EC0 value (16 hours) was found for P. putida with 125 mg/L. The EC50 values determined in the experiments of Elnabarawy et al. (1988) applying the respiration inhibition test to activated sludge exposed to chloroform for 30 minutes or three hours ranged from 840 to 1010 mg/L.

A well documented study using activated sludge has been performed by Blum and Speece (1991). Three different species were considered applying different criteria for the characterisation of adverse effects. The respiration inhibition test was applied to aerobic heterotrophs and the EC50 value (15 hours) was 640 mg/L. A second test on the inhibition of gas production was carried out with methanogens and the EC50 value determined after 48 hours was considerably lower: 0.9 mg/L. A third test with Nitrosomas bacteria, which convert ammonium nitrogen to nitrite as the first step of oxidation, investigated the inhibition of ammonium consumption and the EC50 value determined after 24 hours was lowest: 0.48 mg/L.

The available studies indicate that chloroform has the most adverse effect on ammonium converting bacteria and also on methanogenic bacteria. In contrast, aerobic bacteria seem to be more resistant with regard to exposure to chloroform. The lowest EC50 value of 0.48 mg/L is considered in the risk assessment to represent the toxicity of chloroform to microorganisms.