Bioaccessible metals in dust materials from non-sulfide Zn deposit and related hydrometallurgical operation.

Mining and processing of ores in arid (desert) areas generates high amounts of dust, which might be enriched in potentially harmful elements. We studied dust fractions of ores, soils, and technological materials from mining and related hydrometallurgical operation at former Skorpion Zinc non-sulfide Zn deposit in southern Namibia (closed and placed under maintenance in 2020). Chemical and mineralogical investigation was combined with oral bioaccessibility testing of fine dust fractions (<48 µm and <10 µm) in simulated gastric fluid (SGF) to assess potential risk of intake of metallic contaminants (Cd, Cu, Pb, Zn) for staff operating in the area. The bulk metals concentrations were largely variable and ranked as follows: soils < tailings â‰ª Skorpion ores < imported ores and dross used for feed ore blending. Maximum contaminant concentrations in the original granular materials were 927 mg Cd/kg, 9150 mg Cu/kg, 50 g Pb/kg and 706 g Zn/kg, respectively, and generally increased as a function of decreasing grain size. The highest bioaccessible concentrations of Cd and Pb yielded imported ores from Taiwan and Turkey and, together with the milled dross, these samples also exhibited the highest Zn bioaccessibilities. The exposure estimates calculated for a worker (weighing 70 kg) in this mining/ore processing operation at a dust ingestion rate of 100 mg/day indicated that most dust samples (soils, tailings, Skorpion ores) exhibited metals intake values far below tolerable daily intake limits. The overall health risk was limited in all mining and ore processing areas except for the ore blending area, where imported ores and recycled dross enriched in bioaccessible Cd, Pb and/or Zn were used for the ore blending. Safety measures required by the mine operator (wearing of masks by the operating staff) helped to prevent the staff's exposure to potentially contaminated dust even in this blending ore area.

Controls on δ26Mg variability in three Central European headwater catchments characterized by contrasting bedrock chemistry and contrasting inputs of atmospheric pollutants.

Magnesium isotope ratios (26Mg/24Mg) can provide insights into the origin of Mg pools and fluxes in catchments where Mg sources have distinct isotope compositions, and the direction and magnitude of Mg isotope fractionations are known. Variability in Mg isotope compositions was investigated in three small, spruce-forested catchments in the Czech Republic (Central Europe) situated along an industrial pollution gradient. The following combinations of catchment characteristics were selected for the study: low-Mg bedrock + low Mg deposition (site LYS, underlain by leucogranite); high-Mg bedrock + low Mg deposition (site PLB, underlain by serpentinite), and low-Mg bedrock + high Mg deposition (site UDL, underlain by orthogneiss). UDL, affected by spruce die-back due to acid rain, was the only investigated site where dolomite was applied to mitigate forest decline. The δ26Mg values of 10 catchment compartments were determined on pooled subsamples. At LYS, a wide range of δ26Mg values was observed across the compartments, from -3.38 ‰ (bedrock) to -2.88 ‰ (soil), -1.48% (open-area precipitation), -1.34 ‰ (throughfall), -1.19 ‰ (soil water), -0.99 ‰ (xylem), -0.95 ‰ (needles), -0.82 ‰ (bark), -0.76 ‰ (fine roots), and -0.76 ‰ (runoff). The δ26Mg values at UDL spanned 1.32 ‰ and were thus less variable, compared to LYS. Magnesium at PLB was isotopically relatively homogeneous. The δ26Mg systematics was consistent with geogenic control of runoff Mg at PLB. Mainly atmospheric/biological control of runoff Mg was indicated at UDL, and possibly also at LYS. Our sites did not exhibit the combination of low-δ26Mg runoff and high-δ26Mg weathering products (secondary clay minerals) reported from several previously studied sites. Six years after the end of liming at UDL, Mg derived from dolomite was isotopically undetectable in runoff.