TIME TRENDS IN LEVELS, PATTERNS, AND PROFILES FOR POLYCHLORINATED DIBENZO-P-DIOXINS, DIBENZOFURANS, AND BIPHENYLS IN A SEDIMENT CORE FROM THE BALTIC PROPER

A rural laminated sediment core from the northwestern part of the Balt ic 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/dibenzof urans (PCDD/Fs) and seven congeners of chlorinated biphenyls (PCBs). B oth PCDD/Fs and PCB were detected in small but significant levels duri ng the period 1882-1962 (total PCD D/F 92-234 pg/g). The proposed sour ces are combustion of various natural items like coal, wood, and peat. Increased PCDD/F and PCB levels were found during the period 1970-198 5 (total PCDD/Fs 520-1800 pg/g). The increased concentrations coincide with a change in PCDD/F congener profiles and isomeric patterns. Deta iled examination of the profile and pattern demonstrates that chloroor ganics, and among them penta chlorophenol (PCP), are the main contribu tors to PCDD/Fs. Polychlorinated alkyldibenzofurans (alkyl-PCDFs) were detected in the 1985 and 1978 disks, providing evidence of coastal tr ansport and demonstrating the impact of pulp mill chlorine bleaching a ctivities. The transport time for particulates with coastal origin is estimated to be in order of decades. This should be compared to the at mospheric input via dry and wet deposition, which is estimated to have a residence time in the water column of a maximum of 2 years. Degrada tion is assumed to be insignificant, but an estimate of minimum half-l ife times for PCDD/F in buried sediment is made.