A chemical and mineralogical reconstruction of Zn-smelter emissions in the Kempen region (Belgium), based on organic pool sediment cores

Abstract

The atmospheric pollution history of a former Belgian Zn-smelter complex is preserved in organic sediments of a nearby peat bog pool. The stratigraphy of trace metals, Pb-isotope ratios and mineralogy indicate extreme heavy metal pollution in recent sediments. In the pollutant trend, extremes coincide with maxima in 20th century metal production, minima during major war conflicts and the final shutdown of the smelter. Peak pollution concentrations measure up to 4.7 wt.% Zn, 1.1 wt.% Pb and 0.1 wt.% Cd, which correspond to calculated atmospheric deposition rates of 9.0, 1.6 and 0.16 g m −2 yr −1, respectively. 206Pb/ 207Pb isotope ratios show higher values in the polluted interval (1.135–1.162) relative to local geogenic values deeper down-core (1.194–1.215). Within the polluted interval, three significantly different 208Pb/ 206Pb plateaus are recognized and suggested to indicate changes in the origins of processed ores. Microprobe analyses on sediment thin sections show extensive in situ FeS 2 and ZnS precipitation, which suggests that anoxic processes are responsible for the immobilization of the atmospheric metal inputs. The occurrence of oxidized smelter dusts in an independent surface soil sample indicates a rapid diagenetic transformation of metal oxides into sulfides. Morphology and chemical characteristics allow the distinction between smelter related and diagenetic mineral deposits, and give evidence for dust from open-air ore repositories, as well as smelter operation without dust filters.