Insights into the global distribution of polychlorinated dibenzo-p-dioxinsand dibenzofurans

Polychlorinated dibenzo-p-dioxins and dibenzofurans were measured in 63 pai rs of tree bark and soil samples. Maps of lipid-adjusted concentrations in bark and fluxes to soil indicated that Vancouver Island, the Midwestern Uni ted States, Germany, and Hong Kong were areas of high PCDD/F deposition. Co ncentrations and fluxes in the regions north of the 60th parallel, particul arly the Canadian Arctic, were low, indicating that PCDD/F do not move appr eciably from warm to cold latitudes. Linear regressions of the PCDD/F conce ntrations in tree bark versus fluxes to soil showed that total concentratio ns in bark can be used to estimate total fluxes to soil ina particular regi on. Comparison of the homologue profiles for each pair of bark and soil sam ples indicated that the pairs fell into three categories: 1. bark and soil both resembled source profiles; 2. bark and soil both resembled sink profil es; and 3. bark resembled a source profile but the soil resembled a sink pr ofile. This variation in homologue profiles may be due to the proximity of sampling locations to sources. We found that anthropogenic NO, emissions ar e highly correlated to PCDD/F soil fluxes, and we used this regression to e stimate global PCDD/F fluxes to soil on the same spatial scale as the NO, d ata. 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/y r.