Measurement of atmospheric deposition of polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) to a soil

A buried soil with very low levels of polychlorinated dibenzo- p-dioxins (PCDDs) and dibenzofurans (PCDFs) was exposed to the atmosphere in three different controlled environments and at an outdoor site. The change in soil concentration was measured with time and used together with ambient air data to calculate atmospheric deposition velocities of the PCDDs and PCDFs. It was demonstrated that measurable dry gaseous deposition of the lower chlorinated congeners occurs at background levels of atmospheric contamination. The average dry gaseous deposition velocity to the soil surface exposed outdoors was 2.08 m h −1 In comparison, the average dry particle-bound deposition velocity of the PCDDs and PCDFs at the outdoor site was 1.03 m h −1 It was estimated that more than two thirds of the dry particle-bound deposition was associated with large particles ( d ae > 2.9 μm). However, these forms of deposition were of secondary importance compared to wet deposition, which contributed 85% of the total deposition of the higher and 60% of the lower chlorinated congeners.