WET AND DRY DEPOSITION OF CHLORINATED DIOXINS AND FURANS

We investigated how wet and dry deposition contribute to the observed changes in polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) homologue profiles between sources and sinks. Sampling methods included wet-only samplers to collect rain and inverted frisbees and flat plates to collect dry deposition. Samples were analyzed by electron capture, negative ionization gas chromatographic mass spectrometry. Rain was collected in Indianapolis, IN. The average, total wet deposition flux of PCDD/F in Indianapolis (at 15-degrees-C) was 220 ng/(m2 yr). Overall scavenging ratios for PCDD/F ranged from 15 000 to 150 000. The amount of PCDD/F which was particulate scavenged by rain increased as temperature decreased. Dry deposition fluxes were measured in Bloomington, IN, and in Indianapolis. The average dry deposition flux (at 15-degrees-C) in Bloomington was 160 ng/(m2 yr) and in Indianapolis it was 320 ng/(m2 yr). Dry deposition fluxes increased as temperature decreased. An average deposition velocity of 0.2 cm/s was calculated for PCDD/F homologues. Both wet and dry deposition, which are important mechanisms for the removal of atmospheric PCDD/F, contribute to the enhancement of 8D observed in the sediments.