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76 A. Lukin et al. / The Science of the Total Environment 306 (2003) 73-83 Table 1 Average concentrations of heavy metals (mg/g dry wt.) in surface (0-1 cm) and background (deeper than 20 cm) sediments and values of the contamination factor (Cf)a for heavy metals in Lake Kuetsjarvi Ni Cu Co Zn Cd Pb Hg Fe Mn Surface 2218 905 120 261 1.61 19 0.400 55500 4140 Background 85 63 22 126 1.16 12 0.035 46900 2290 Cf 26.0 14.3 5.5 2.1 1.4 1.6 11.4 1.2 1.8 a Cf = surface concentration /background concentration. Kuetsjarvi. During the study period pH values ranged between 6.5 and 7.1. Sulfate content varied between 30.7 and 41.7 mg l -1 . The concentrations of the main pollutant-elements were 58-103 mg l -1 for Ni, 7-94 mg l -1 for Cu, 5-66 mg l -1 for Zn, 5-138 mg l -1 for Mn. These were one to two orders of magnitude higher than the average back­ ground levels for unpolluted areas of the Mur­ mansk Region (Moiseenko et al., 1995) and they demonstrate indicate the intensive loading of the main polluting elements into the water column of the lake. 3.1. Sediments Background concentrations of heavy metals in sediment cores from Lake Kuetsjarvi ranged between 49 and 173 mg g -1 for Ni, 38 and 96 mg g -1 for Cu, 5 and 34 mg g -1 for Co, 106 and 163 mg g -1 for Zn, 0.25 and 1.82 mg g -1 for Cd and 5 and 29 mg g -1 for Pb. Mean concentrations are given in Table 1. Average background concentra­ tions of heavy metals are at the same levels found in other lakes investigated in the Kola Peninsula (Dauvalter, 1994, 1997). Historical changes in the vertical distribution of heavy metals in sediments with increasing concen­ trations towards the sediment surface are evident in the core from station 3 of Lake Kuetsjarvi (Fig. 2). This pattern is particularly typical for Ni, Cu, Zn and Co as they are the dominant pollutants in this area, as a result of emissions from the Pech- enganickel smelter (Fig. 2 ). Lead and Mn also show this vertical distribution pattern. Sediment core dating was not performed for the sediments; therefore no direct estimate of the sedimentation rate could be derived. Intensive increase of emis­ sions from Pechenganickel began in 1972 Fig. 2. Distribution of heavy metal concentrations in sediment core from station 3 on Lake Kuetsjarvi.