Tolerable daily intake dose
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tolerable daily intake dose (TDI), a theoretical concept of regulatory toxicology giving the highest dose of a chemical which can be assured to be safe even if one is exposed to the chemical through the whole lifetime. Most TDI values have been estimated on the basis of animal experiments. Usually the TDIs include safety margins to guarantee safety even if human being should be more sensitive than the animal. The safety margin is often 100-fold, but could be larger, if research data is not satisfactory. If the chemical is carcinogenic (see this), different methods are used in different countries. Some countries use large safety margin (e.g. 1000-fold), some use mathematical extrapolations (see this) to reach a level deemed safe (e.g. a maximum likelihood of one in a million chance of contracting cancer due to a lifetime exposure to the chemical). The important point is that the purpose of TDI is to serve regulators in administrative work, and not individual persons. It does not predict the likelihood of individual's health effect in any reliable way, if the limit is exceeded. TDIs of dioxins set by various authorities in different countries vary by more than thousandfold, which illustrates the difficulties in dioxin risk assessment. The latest recommendation for TDI for the sum of dioxins and dioxin-like PCBs is 1 to 4 pg/kg/day (WHO-TEq per b.w.), in other words, in 70-kg person 70 to 280 pg/day. This should be understood as the average intake over a long period of time (see cumulation).