Threshold of Toxicological Concern (TTC)

Literature review and applicability

image of Threshold of Toxicological Concern (TTC)

In the regulation of food contact articles and flavouring substances, the TTC concept (Threshold of Toxicological Concern) has been developed as a substitute for substance-specific information. The TTC concept is based on the analysis of the toxicological and/or structural data of a broad range of different chemicals, with the aim to set an exposure-value below which no toxicity testing is necessary. Recently, application of the TTC concept has been proposed as a tool in risk assessment of industrial chemicals within REACH, both for defining when no testing is needed based on exposure information and as a substitute for effect values. The proposal concerns both human health and the environment. The present report does not advocate the use of TTC instead of substance specific toxicity data for risk assessment of industrial chemicals within REACH at time being. This conclusion is based on current knowledge and understanding of the concept, and on limitations and uncertainties in the derivation of TTCs. Furthermore, the suitability of the TTC concept so far has not been evaluated for the diverse group of industrial chemicals. In addition, the possible consequences for the level of protection of human health and the environment resulting from applying the TTC concept in the risk assessment should be examined.




Two different approaches have been used when deriving a TTC for the environment, i.e. the “action-limit” proposed by EMEA/CPMP (2001) and the environmental Exposure Threshold of No Concern (ETNC) proposed by ECETOC (2004) and de Wolf et al. (2005). Both these approaches are restricted to the pelagic freshwater compartment. The approaches are described briefly here, while more specific information is presented in the literature review below.


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