Lead Isotopic and Metallic Pollution Record in Tree Rings from the Copperbelt Mining–Smelting Area, Zambia

Mihaljevič, Martin; Ettler, Vojtéch; Šebek, Ondřej; Sracek, Ondra; Kříbek, Bohdan; Kyncl, Tomáš; Majer, Vladimír; Veselovský, František

Lead Isotopic and Metallic Pollution Record in Tree Rings from the Copperbelt Mining–Smelting Area, Zambia

2011

The composition of tree rings and soils was studied at several locations affected by smelting and transportation in the vicinity of Kitwe (Copperbelt, Zambia). The contents of cobalt (Co), copper (Cu), manganese (Mn), and lead (Pb) and the 206Pb/207Pb isotope ratios in the tree rings were interpreted in relation to potential sources of contamination such as smelter production, acidification of the environment, soil composition, raw material processing, and atmospheric suspended particulate matter (SPM). The highest Co contents in the tree rings correspond to maximum ore production in the mid-1970s. Acidification through SO2 emissions is documented in the increased Mn contents from the mid-1980s. The isotopic composition of the tree rings of the studied tree species varies in the interval 1.16–1.34 and the youngest parts of all the studied trees exhibit a low 206Pb/207Pb ratio (<1.17). The soil isotope composition varies in the range 206Pb/207Pb = 1.18–1.35. The Pb isotope composition in the soils and tree rings was formed by a combination of lithogenic Pb (206Pb/207Pb ∼ 1.3), Pb in processed ores (206Pb/207Pb ∼ 1.2), and SPM (automobile) Pb (206Pb/207Pb∼1.1). As the soils in the distant region have high 206Pb/207Pb ratios (>1.3) in the whole profile and simultaneously the youngest parts of the tree rings of tree species growing in this soil have a low 206Pb/207Pb ratio (<1.17), it can be assumed that the Pb in the youngest parts of the tree species is derived from absorption of SPM Pb through the bark rather than root uptake. The absence of Pb with a low 206Pb/207Pb ratio in soils in the distant area is probably affected by fires in the herbaceous and bush undergrowth and plant litter, which prevents Pb from biomass from entering the soil and mobilize it back into the atmosphere.

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