Copper isotopic record in soils and tree rings near a copper smelter, Copperbelt, Zambia

The copper (Cu) content and isotopic composition were studied in soils and in pine tree rings at locations close to and far from the Cu smelter, located at Kitwe, Zambia. The soil in the remote area contained 25–75 mg kg^{− 1} Cu, whereas the soil close to the smelter contained 207–44,000 mg kg^{− 1} Cu. The δ⁶⁵Cu at the remote area and close to the smelter varied in the range − 0.40 to − 0.11‰, and − 0.44 to 0.01‰ respectively. The δ⁶⁵Cu of the surface soil at both profiles (− 0.44 to − 0.40‰) is similar to the isotopic composition of the concentrates processed in the smelter (− 0.75 to − 0.45‰), i.e. both locations are affected by Cu ore dust. The increase in the δ⁶⁵Cu in the direction towards the centre of the profile is caused by the oxidative dissolution of Cu(I) from ore minerals, during which heavier Cu is released. In deeper parts of the profile, there is a slight decrease in δ⁶⁵Cu because of easier mobilisation of the lighter isotope. The tree rings at the two locations differ in the total contents and isotopic composition. At the less contaminated site, the Cu contents equal 0.4 to 1.1 mg kg^{− 1} while, at the polluted site, the Cu contents vary in the range 3 to 47 mg kg^{− 1}. Whereas, at the less contaminated location, the tree rings are substantially enriched in lighter Cu (δ⁶⁵Cu = − 0.76 to − 2.2‰), at locations close to the smelter the tree rings have an isotopic composition (− 0.31 to − 0.88‰) similar to that of the contaminated soil or processed ore. The isotopic compositions of the tree rings close to the smelter are affected particularly by interception of dust containing Cu ore. The δ¹³C in tree rings demonstrate the interconnection of acidification and Cu mobility.