Nordic Project Applicability of TTC within REACH

A Nordic project has evaluated how different TTC-like concepts have been used, and assessed their potential usability in risk assessment of industrial chemicals within REACH (NCM 2005). The Nordic group considered that if the TTC concept is appropriately derived and used, it might imply a better focus of chemicals at risk. However, it was also stated that, independent of the approach used in risk assessment of industrial chemicals, it is important to maintain a sufficient level of protection and that application of the TTC concept in REACH would imply that limited data may be generated and thus that the level of protection might be influenced. 

The Nordic group noted a number of limitations or drawbacks that should be taken into consideration in deciding whether the TTC concept in general might be applicable for use within REACH (NCM 2005)  

In general, the consequences of the assumptions of toxicological, statistical, and/or uncertainty factors made in the derivations of the TTC concepts are difficult to overview since there are uncertainties and drawbacks in more or less all of the available TTC approaches. 

A number of studies have been undertaken to investigate whether different endpoints of concern, which might give rise to effects at low doses like immunotoxic, endocrinologic, neurotoxic, and developmentally toxic effects could be included in the TTC values. The Nordic group considered that not aU these endpoints have been adequately covered by the analyses performed today. 

From the investigations performed it has been concluded that all types of substances cannot be included in a concept using TTC in this respect, the Nordic group pointed out that industrial chemicals are diverse and often of complex namre. 

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