Insights into the global distribution of polychlorinated dibenzo-p-dioxins and dibenzofurans

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 ina 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, 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, 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.