| Popis: |
A rural laminated sediment core from the northwestern part of the Baltic Proper (station P18) was sliced into nine dated disks. (Average age : 1882, 1906, 1922, 1938, 1954, 1962, 1970, 1978, and 1985). Each disk was analyzed for tetra- to octachlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and seven congeners of chlorinated biphenyls (PCBs). Both PCDD/Fs and PCB were detected in small but significant levels during the period 1882-1962 (total PCDD/F 92-234 pg/g). The proposed sources are combustion of various natural items like coal, wood, and peat. Increased PCDD/F and PCB levels were found during the period 1970-1985 (total PCDD/Fs 520-1800 pg/g). The increased concentrations coincide with a change in PCDD/F congener profiles and isomeric patterns. Detailed examination of the profile and pattern demonstrates that chloroorganics, and among them pentachlorophenol (PCP), are the main contributors to PCDD/Fs. Polychlorinated alkyldibenzofurans (alkyl-PCDFs) were detected in the 1985 and 1978 disks, providing evidence of coastal transport and demonstrating the impact of pulp mill chlorine bleaching activities. The transport time for particulates with coastal origin is estimated to be in order of decades. This should be compared to the atmospheric input via dry and wet deposition, which is estimated to have a residence time in the water column of a maximum of 2 years. Degradation is assumed to be insignificant, but an estimate of minimum half-life times for PCDD/F in buried sediment is made. |
