Dioxins are fat-soluble, and accumulate in organisms from dietary sources.
Because these compounds persist in tissue, they bioaccumulate in the food chain to levels that are often thousands of time higher that in the surrounding environment. Thus, higher predators and older organisms contain the highest concentrations of dioxin. The bioaccumulation factor in fish is thought to be as much as 100,000 times ambient, depending on the species and the environmental conditions. In Maine, a law enacted in 1997 will require paper mills and other dioxin sources to comply with the upstream-downstream mandate by the year 2001. This simply means that fish downstream of the mill must have concentrations no higher than fish upstream.