[Reconstruction of temporal and spatial trends of atmospheric pollution based on polychlorinated biphenyls concentration changes in ombrotrophic bogs]

To reconstruct the deposition rate of polychlorinated biphenyls (PCBs) in different historical periods and to examine the temporal and spatial trend of PCBs pollution, we analyzed the changes of PCBs concentration and deposition rate in peat cores and lake sediments, and evaluated the suitability of peat cores and lake sediments for studying PCBs deposition trend. Through the dating analysis of all samples, we found that peat bog could well record the historical sedimentation of PCBs. PCBs did not degrade in peat, and it was thus feasible to use peatland to examine the settlement of PCBs. In this study, the reconstruction time of ∑₁₁PCBs in peat was from the beginning of 19th century to the beginning of 21st century. The mean inventory of ∑₁₁PCBs in three peat cores of each bog changed between (37.0±5.4) and (47.2 ±27.8) μg·m^-2, with the standard deviation between 14.9% and 58.9%. The highest concentration of ∑₁₁PCBs was 6.8 ng·g^-1DW, while the maximum deposition rate of reconstructed PCBs was up to 989.7 ng·m^-2·a^-1. The trend of deposition rate was first increasing and then decreasing. After the year 1980, the deposition rate was substantially decreasing, which was consistent with the prohibition of PCBs production in the United States in 1979. Meanwhile, the analysis of sediment samples in the lake near bog showed that concentration and maximum deposition rate of the lake sediment were comparable to those of the nearby bog. The concentrations of Di- to Hepta-PCB congeners were evenly distributed along the sediment profile. Therefore, lake sediments could not be used to analyze the historical sedimentary model of low order PCBs. This study reconstructed temporal and spatial variation of PCBs in atmospheric environment in different historical periods, which could provide basic data for the evaluation of regional environmental quality.