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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

There are two key studies in this section addressing different aspects relating to biological degradation of trichloroethane. The first study conducted by Wood et al 1980 was part of the much larger study initiated by the EPA to ascertain levels of trichloroethane in natural aquifers used for production of drinking water. The results of the study show that the incidence of trichloroethane contamination is restricted to sites where the risk of contamination is high (in this case close to a chemical plant producing chlorinated aliphatic compounds).  The paper also contains results of mini mesocosm studies conducted with natural bacterial populations present in muck soils taken from the Florida  Everglades. The results of this study show that under anaerobic conditions the DT50 for trichloroethane is 15.6 days.
In a second study conducted by Blum and Speece 1980 the toxicity of trichloroethane to aerobic and anaerobic cultures was addressed. The results of this study showed that the IC50 for Nitrosomonas, anaerobic methanogens and aerobic hetyrotrophs were 8.5, 0.52 and 450 mg/L respectively.

Key value for chemical safety assessment

Additional information

The literature does not contain any studies addressing the simple biodegradation as per OECD guidelines. The two studies included in this section consist of a Tier III mini microcosm study and a Tier II study conducted on natural populations present in waste water treatment plants. Both studies were conducted in sealed vessels thereby eliminating losses through volatilisation. In the case of the first study (Woods et al 1980) following a literature review the authors conclude that degradation was most likely to occur under anaerobic conditions. To test this hypothesis an anaerobic muck soil was obtained from the Florida Everglades. Tests showed that naturally occurring bacterial populations were capable of utilising 1,1,1-trichloroethane resulting in a DT50 value of 15.6 days which justified the author's conclusion that trichloroethane was inherently biodegradable. However, it should be pointed out that the primary degradation products was 1,1 -dichloroethane which is comparatively persistent under anaerobic conditions and could therefore persist in the environment. Results from aerobic studies show that 1,1 -dichloroethane is readily degraded by aerobic bacteria. It can therefore be concluded that in order to remove trichloroethane from contaminated waste a period of anaerobic fermentation is necessarily followed by aerobic fermentation to complete breakdown of the parent material.

Blum and Speece 1980 did not address biodegradation directly but instead looked at the inherent toxicity of trichloroethane to species expected to be present in commercial sewage treatment plants. In this study the toxicity of 1,1,1-trichloroethane to a range of bacteria (methanogens, Nirosomonas and aerobic hetrotrophs) was studied. The results of the study showed that the most sensitive bacteria to 1,1,1-trichloroethane under the conditions of the study were methanogens (IC50: 0.52mg/L) followed by Nirosomonas (IC50: 8.5mg/L). Aerobic hetrotrophs were extremely tolerant (IC50: 450mg/L) to trichloroethane.