EU Approach Industrial Chemicals

Within the EU chemical s regulation, a more simple approach based on the dose descriptor T25 has been proposed as a basis for quantitative risk characterization of non-threshold carcinogens. 

The following overview of the T25 approach is primarily based on the papers by Dybing et al. (1997) and Sanner et al. (2001). 

The T25 was originally proposed as a simplihed carcinogenic potency index as a practical method for potency considerations in carcinogen classihcation systems (Dybing et al. 1997) and is used within the EU context of classihcation and labeling of chemical substances (see Section 2.4.1.8) for inclusion of potency considerations in setting specihc concentration limits for carcinogens in Annex I of Directive 67/548/EEC (EC 1999). 

The T25 is dehned as the chronic daily dose (in mg/kg body weight per day), which will give 25% of the animal s tumors at a specihc tissue site, after correction for spontaneous incidence, within the standard lifetime of that species. It is a value calculated from a single observed dose-response and based upon the assumphon of a linear dose-response relationship over the entire dose range. 

The T25 value may either be incidentally obtained from the experimental smdy or calculated from other mmor incidences at the selected tumorigenic dose (determined above), using linear extrapolation, i.e., by multiphcahon of the dose with the factor 25/p where p is the acmal mmor incidence (e.g., in case of a net 15% incidence, multiply by 25/15). 

---