The use of Scots pine (Pinus sylvestris L.) bark as a bioindicator for environmental pollution monitoring along two industrial gradients in the Kemi-Tornio area, northern Finland

This paper describes the use of Scots pine (Pin us sylvestris L.) bark as a passive boindicator for environmental pollution monitoring in the immediate vicinity of the ferrochrome and stainless steel works of Outokumpu Stainless Oy at Tornio and of the opencast chromium mine of Outokumpu Chrome Oy Kemi Mine at Kemi, Northern Finland. According to the pollution factors (PF; i.e. the ratio of heavy metal concentrations in the bioindicators to those in the background area), the average Cr, Fe and Ni concentrations in bark samples around the works were 81, 7 and 5.9 times higher, respectively, compared with the levels in the background area. In the areas subjected to emissions from the mine, the PF values for Cr, Fe and Ni were 5.3, 12.4 and 3.0, respectively. In the vicinity of the works, the PF values followed the order Cr > Mo > Ni > Fe > Ti > Zn, but in the vicinity of the mine, the order Cr > Ti > Fe > Ni > Zn > Mo. In addition, two different microwave-assisted digestion procedures, i.e. a mixture of HNO3 + H2O2, and a mixture of HNO3 + HCl + HF, were compared for digestion of heavy metals (Ti, Cr, Fe, Ni, Zn and Mo) in Scots pine (Pinus sylvestris L.) bark samples. According to the results, the digestion procedures with a mixture of HNO3 + H2O2, which is commonly used in bioindicator studies, underestimated heavy-metal concentrations in the bark samples. For the bark samples collected in the immediate vicinity of the point sources, which emit chromium in the chemical forms of (Fe,Mg)(Cr,Al)(2)O-4 and FeO-Cr2O4, the digestion procedure with a mixture of HNO3 + HCl + HF gave 65%, 101% and 29% higher values for Ti, Cr and for Fe, respectively, than the digestion procedure with a mixture of HNO3 + H2O2.