The implication is that low doses are important. First, it recognizes that the human background estimates of exposure to dioxins is going down. Cancer risk from animal studies has increased about five-fold because of some of the gerrymandering you heard this morning. TCDD is now classified as a human carcinogen. There is an emphasis on body burden, as you have heard, rather than dose per day, as the dose metric to scale between species.
Epidemiology plays a greater role in risk assessment.
It is interesting to compare that with what the National Academy says about low level carcinogens in the diet. Dolan Pito's estimate of the risk from the diet is about one third of the total risk for cancer. The NAS explanation for the risk from carcinogens in the diet is primarily the promoting effect of fat on the thousands of carcinogens that you normally eat. EPA is taking a different view. They think a good portion of that risk is due to dioxin, despite that it is present in very, very small doses.