Trichloroethylene

PBT assessment

PBT assessment: overall result

PBT status:

the substance is not PBT / vPvB

Justification:

Trichloroethylene is a monoconstituent substance with a purity of > 99.9%. There is no other constituent or impurity that requires assessment for PBT except for the main. 

Persistence assessment:

The degradation of trichloroethylene by various abiotic and biotic processes has been examined in the relevantenvironmental media. 

Hydrolysis is not expected to be an important removal process for trichloroethylene. Half-lives in the range from 10.7 months to 1.3 million years have been reported (Dilling et al., 1975; Jeffers et al 1989).  Photolysis is also unlikely to be a significant removal process for trichloroethylene in aquatic environments.

 

Trichloroethylene undergoes reactions with hydroxyl radicals in the atmosphere. The calculated half life of trichloroethylene due to this reaction is 13.3 days with an OH radical concentration of 1.5E6 OH/cm3 (AOPWIN, 2000), with an overall OH-rate constant of 8.048E-13cm3/molecule.sec. Trichloroethylene also reacts with ozone, nitrate radicals, hydroperoxy radicals, and chlorine atoms in the atmosphere, but this is thought to be an insignificant atmospheric degradation processes. Overall, trichloroethylene is degraded in the atmosphere.

 

A number of studies have been reported on the biodegradation of trichloroethylene. The substance was not biodegraded under the stringent conditions of the modified shake flask closed bottle biodegradation test (Rott et al, 1982; CSCL, 1992). In contrast, trichloroethylene can be co-oxidized under aerobic conditions when other suitable co-substrates (methane, propane, toluene, phenol) are present to support the growth of the microorganisms and induce the formation of enzymes, which due to their broad substrate specificity, can also degrade trichloroethylene.

 

There is extensive work which shows that under anaerobic conditions, trichloroethylene degrades by a process of reductive dehalogenation, resulting in the formation of lower chlorinated homologues as reaction intermediates. The compound was completely degraded (100%) in sediment samples after 42.5 to 90.3 days (Barrio-Lage et al., 1987). Although metabolites are known to occur, the terminal product of reductive dehalogenation is ethylene. The conditions and inocula used appear to be important.

 

In view of the available information and the criteria summarized in Annex XIII, it is concluded that trichloroethylene meets the criteria for persistence (P and vP).

Bioaccumulation assessment:

Experimental BCF values are available for the assessment of trichloroethylene. The highest observed BCF in fish was 90 l/kg, based on the results of a flow-through exposure study with concentration monitoring. Based on these results, there is low potential for bioaccumulation and therefore trichloroethylene does not meet the B or vB criteria.

 

Toxicity assessment: 

The acute effect concentrations for all three trophic levels are much higher than the screening criterion of 0.1 mg/l. It can be expected that trichloroethylene is not potentially toxic towards aquatic organisms. The chronic effect concentrations for invertebrates and algae were higher than the defined criterion of 0.01 mg/l. In contrast, trichloroethylene is classified as being carcinogenic, category 2, and thus needs to be considered as a CMR. Therefore, trichloroethylene is considered to fulfill the T criteria.