The threshold of toxicological concern (TTC) approach centres on the idea that, even for chemicals with incomplete toxicity profiles, a level of exposure can be predicted below which there is no appreciable risk to human health. EFSA has recently evaluated the relevance and reliability of this concept, including consideration of a decision tree approach based on structural considerations that places chemicals into one of three ‘Cramer’ toxicity classes (I, II or III in order of increasing likely toxicity). Having reviewed the relevant published literature, and carried out independent analyses, EFSA has expressed support for the existing exposure threshold values given to substances with a structural alert for genotoxicity (0.0025 µg/kg bw/day) and those in Cramer Class I (30 µg/kg bw/day). However, the EFSA scientists proposed that the TTC value of 1.5 µg/kg bw/day, traditionally used for Cramer Class III substances alone, should additionally be applied to chemicals in Class II (previously a value of 9 µg/kg bw/day had been used for this group). Meanwhile, a TTC value of 0.3 µg/kg bw/day was viewed as sufficiently protective for organophosphates and carbamates with anti-cholinesterase activity. As exceptions, a number of chemical categories were defined for which the TTC approach was judged inappropriate, including metals, proteins and highly potent carcinogens. Further discussions by EFSA covered the use of TTCs for non-oral routes of exposure, and the derivation of TTCs for young children, with the recommendation that the TTC approach should be considered on a case-by-case basis for infants below six months of age.

[EFSA Scientific Committee (2011). Draft scientific opinion on exploring options for providing preliminary advice about possible human health risks based on the concept of Threshold of Toxicological Concern (TTC). Obtainable from the website of the European Food Safety Authority at online.] {188140}

The above item was taken from the September 2011 issue of Toxicology and Regulatory News which is sent automatically to members of bibra (click here for more details).

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