Global Mass Balance for Polychlorinated Dibenzo-<i>p</i>-dioxins and Dibenzofurans

Abstract

Chlorinated dioxins and dibenzofurans (PCDD/F) were measured in 107 soil samples globally, and depositional fluxes were determined. Deposition to land surfaces was estimated by dividing the earth into five depositional zones based on climatic and geographical factors. Mean depositional fluxes to these zones ranged from 18 to 610 ng m-2 yr-1. Low 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 oceans was estimated to be about 610 ± 1500 kg/yr, yielding a total global deposition of 13 100 ± 2000 kg/yr from the atmosphere. Emissions of PCDD/F to the global atmosphere were estimated by determining emission factors and production rates for the major PCDD/F sources. The major sources considered in this study were municipal waste incineration, biomass combustion, steel and copper mill emissions, cement kiln emissions, medical waste incineration, and emissions from automobiles Total annual emissions were estimated to be 3000 ± 600 kg. Global deposition (see above) is roughly four times greater than annual emissions. This suggests that sources of PCDD/F are not well-characterized. More data are needed on emission factors (particularly from developing countries) and on introduction rates of PCDD/F to the global atmosphere.