Transfer from Food to Humans

The primary sources of human exposure to PCDD/Fs were outlined in the introduction. For North America and Western Europe, uptake of these compounds is about equally divided between dairy, meat and fish products (see Table 1). The levels in the diet are decreasing in some countries. The most recent estimates for Germany suggest an intake of 55-70 pg TEQ d 1 for adults.76 

Of crucial importance for the potential risk associated with this contamination of the diet is the question how much of the ingested PCDD/Fs is actually absorbed and retained in the body There is, however, remarkably little information on this subject. There is one report of absorption in an adult man where 87% of a single dose of radioactively labelled 2,3,7,8-Cl4DD dissolved in corn oil was taken up.77 In another study, in which only faeces samples from two individuals on an unmodified diet were analysed, it was found that the excretion rate was very high compared to the theoretical uptake rate,78 which would suggest that absorption is low. No work beyond these two somewhat contradictory studies was found. 

Of particular interest is the question of whether or not an absorptive steady state is approached. In this case the net absorption of a compound from the normal diet would be near zero. Human tissue levels might then be determined primarily by highly contaminated foods which are seldom consumed but nevertheless result in a significant absorption of the compound. This would have dramatic consequences for the way risk analysis is done and the identification of means to reduce the risk associated with PCDD/Fs.79 There is an urgent need for more research in this area. 

It is known that the PCDD/Fs are very persistent in humans. Half-lives of most 2,3,7,8-substituted congeners have been measured in occupationally exposed cohorts and found to lie in the range of 5-15 years.80 This results in accumulation in humans, and the concentrations in human fat are at least an order of magnitude higher than in cows milk fat or beef fat.79 As in livestock, the 

---