Abstract
The deposition processes of polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) in Kanazawa, Japan were studied by examination of the concentrations of PCDDs and PCDFs (PCDD/DFs) and their tetra- to octa-chlorinated homologues in the rain. The weighted mean deposition flux was 360 pg/m2/day [7.7 pg-toxicity equivalency quantity (TEQ)/m2/day]. Deposition fluxes obtained in this study were lower than the average value of Japan, suggesting that Kanazawa is a less polluted area. The seasons with the highest and next highest deposition fluxes were winter and spring, respectively, possibly due to the presence of an inversion layer in winter and spring that reduced the atmospheric dilution of pollutants. In addition, the ratio of PCDFs to total deposition flux in winter was larger than the ratios in the other seasons, possibly due to the burning of fossil fuels for residential heating. Deposition flux of each tetra- to octa-chlorinated homologue of PCDD/DFs was negatively correlated with surface temperature. Other meteorological parameters were positively correlated with almost all tetra- to octa-chlorinated homologues, except for heptachloro dibenzo-p-dioxins (HpCDDs) and octachloro dibenzo-p-dioxin (OCDD), possibly as a result of the photochemical reaction of pentachlorophenol (PCP), which produced mainly OCDD and traces of HpCDDs. In ambient air, the two most dominant homologues were tetrachloro dibenzo-p-dioxins (TeCDDs) and OCDD, while, in soil, the two most dominant homologues were OCDD and TeCDDs. The washout ratios increased with the increase in chlorine substitution. Thus, the difference in washout ratios between homologues might be one of the reasons for the difference of the homologue profile between the air and soil.
