Stable isotope tracing of Ni and Cu pollution in North-East Norway: Potentials and drawbacks.

The use of Ni and Cu isotopes for tracing contamination sources in the environment remains a challenging task due to the limited information about the influence of various biogeochemical processes influencing stable isotope fractionation. This work focuses on a relatively simple system in north-east Norway with two possible endmembers (smelter-bedrock) and various environmental samples (snow, soil, lichens, PM). In general, the whole area is enriched in heavy Ni and Cu isotopes highlighting the impact of the smelting activity. However, the environmental samples exhibit a large range of δNi (-0.01 ± 0.03‰ to 1.71 ± 0.02‰) and δCu (-0.06 ± 0.06‰ to -3.94 ± 0.3‰) values which exceeds the range of δNi and δCu values determined in the smelter, i.e. in feeding material and slag (δNi from 0.56 ± 0.06‰ to 1.00 ± 0.06‰ and δCu from -1.67 ± 0.04‰ to -1.68 ± 0.15‰). The shift toward heavier Ni and Cu δ values was the most significant in organic rich topsoil samples in the case of Ni (δNi up to 1.71 ± 0.02‰) and in lichens and snow in the case of Cu (δCu up to -0.06 ± 0.06‰ and -0.24 ± 0.04‰, respectively). These data suggest an important biological and biochemical fractionation (microorganisms and/or metal uptake by higher plants, organo-complexation etc.) of Ni and Cu isotopes, which should be quantified separately for each process and taken into account when using the stable isotopes for tracing contamination in the environment.