As illustrated in this figure, the cycling of dioxin through the environment is a complex process, involving multiple Sources, Flows, Reservoirs, and Sinks. Sources to air are dominated by the combustion of wastes and fuels. Sources to water include storm runoff, air deposition, and waste water discharges from certain industrial processess. Contributions to land include air deposition and the land spreading of waste water treatment sludge. Reservoirs include soil, sediment and manufactured materials which contain dioxins that are temporarily stored but may later be released into the circulating environment.
Sinks represent the long term storage and isolation of dioxin in undisturbed soil and sediment.
Although we have a general qualitative understanding of dioxin cycling in the environment, our quantitative understanding is limited. The fundamental goal of the initiative is to quantitatively link dioxin sources to general population exposure. This is being accomplished by pursuing two simultaneous lines of inquiry. One approach is to focus on identifying sources of dioxin-like compounds and work forward along their pathways of transport and deposition. The second is to start with human body burdens and work backwards through the process of bioaccumulation and uptake.