GLOBAL MASS-BALANCE FOR POLYCHLORINATED DIBENZO-P-DIOXINS AND DIBENZOFURANS

Chlorinated dioxins and dibenzofurans (PCDD/F) were measured in 107 so il samples globally, and depositional fluxes were determined. Depositi on to land surfaces was estimated by dividing the earth into five depo sitional zones based on climatic and geographical factors. Mean deposi tional fluxes to these zones ranged from 18 to 610 ng m(-2) yr(-1). Lo w fluxes were observed in most zones not impacted by industrialization . Total global deposition from the atmosphere to land was estimated to be 12 500 +/- 1300 kg/yr. Based on limited data, deposition to the oc eans was estimated to be about 610 +/- 1500 kg/yr, yielding a total gl obal deposition of 13 100 +/- 2000 kg/yr from the atmosphere. Emission s of PCDD/F to the global atmosphere were estimated by determining emi ssion factors and production rates for the major PCDD/F sources. The m ajor sources considered in this study were municipal waste incineratio n, biomass combustion, steel and copper mill emissions, cement kiln em issions, medical waste incineration, and emissions from automobiles To tal annual emissions were estimated to be 3000 +/- 600 kg. Global depo sition (see above) is roughly four times greater than annual emissions . This suggests that sources of PCDD/F are not well-characterized. Mor e data are needed on emission factors (particularly from developing co untries) and on introduction rates of PCDD/F to the global atmosphere.