Polychlorinated dibenzo-p-dioxins and dibenzofurans were measured in 63 pairs of tree bark and soil samples. Maps of lipid-adjusted concentrations in bark and fluxes to soil indicated that Vancouver Island, the Midwestern United States, Germany, and Hong Kong were areas of high PCDD/F deposition. Concentrations and fluxes in the regions north of the 60th parallel, particularly the Canadian Arctic, were low, indicating that PCDD/F do not move appreciably from warm to cold latitudes. Linear regressions of the PCDD/F concentrations in tree bark versus fluxes to soil showed that total concentrations in bark can be used to estimate total fluxes to soil in a particular region. Comparison of the homologue profiles for each pair of bark and soil samples indicated that the pairs fell into three categories: 1. bark and soil both resembled source profiles; 2. bark and soil both resembled sink profiles; and 3. bark resembled a source profile but the soil resembled a sink profile. This variation in homologue profiles may be due to the proximity of sampling locations to sources. We found that anthropogenic NO{sub}x emissions are highly correlated to PCDD/F soil fluxes, and we used this regression to estimate global PCDD/F fluxes to soil on the same spatial scale as the NO{sub}x data. Multiplying these fluxes by the corresponding land areas, we estimated that total PCDD/F deposition to the earth's land surface is about 2-15 t/yr.
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