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Soil Contaminants Mobility near Copper Smelters in Zambia

Study on inorganic contaminants' spatial distribution, mobility, and bioaccessibility in soils near copper smelters in Copperbelt, Zambia. Analysis of pollutant levels, Pb isotopic tracing, and health implications. Research funded by Czech Science Foundation and IGCP Project. Conclusions highlight risk to human health from soil ingestion. Study addresses solid speciation, fractionation, and vertical mobility of contaminants.

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Soil Contaminants Mobility near Copper Smelters in Zambia

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  1. Mobility and bioaccessibility of inorganic contaminants in soils in the vicinity of copper smelters (Copperbelt, Zambia) Vojtěch ETTLER1, Martin MIHALJEVIČ1 Bohdan Kříbek2, Vladimír MAJER2, Ondřej ŠEBEK1 1 Charles University in Prague 2 Czech Geological Survey, Prague Czech Republic prepared for Windhoek 2012

  2. Outline of the presentation • Background information (Copperbelt) • Spatial metal/metalloid distribution • Pollutant mobility in soil profiles • Pb isotopic tracing • Gastric bioaccessibility of metals/metalloids • Conclusions and implications Funding: Czech Science Foundation (GAČR 210/12/1413) IGCP Project No. 594 (Assessment of impact of mining…)

  3. Cu-Co mining and smelting (Copperbelt province, Zambia) • 30 Mt Cu produced since 1930s • average ore grade • 3 wt.% Cu • 0.18 wt.% Co

  4. Nkana smelter Screening environmental study • topsoils/subsurface • maximum values • Cu 41900 ppm • Co 606 ppm • Pb 503 ppm • Zn 450 ppm • As 255 ppm Co, Cu – smelter emissions Pb, Zn, As - slags related Cr, Ni – bedrock related Kříbek et al. (2010) J. Geochem. Explor.104, 69-86

  5. Nkana smelter (Kitwe) • in operation 1930-2009 Nkana smelter - view from N

  6. Copperbelt smelter emissions • dust fallout – high metals • Cu 20170 ppm • Co 1542 ppm • Cu-bearing phases • (TEM, XRD) • chalcanthite (CuSO4·5H2O) • delafossite (CuFeO2) • Cu-(Fe) sulphides TEM Cu sulphide Cu sulphate Vítková, Ettler et al. (unpublished data) Vítková et al. (2011) Appl. Geochem. 26, S263

  7. Nkana smelter • 20 Mt of Cu slag • crushing to 15 mm • reprocessing in Chambishi • slag dust generation Cu-Fe sulphides Co-Fe sulphides intermetallic compounds alloys Nkana old slag dumps Vítková, Ettler et al. (2010) Mineral. Mag. 74, 581.

  8. Research questions • Spatial distribution of metals/metalloids • in smelter-affected soils? • Solid speciation/fractionation of inorganic • contaminants? • Vertical mobility in highly polluted soil profile? • Bioacessibility of metals/metalloids?

  9. highly polluted soil profile 110-cm-deep Spatial distribution of metals Cu • 192 topsoils • (Nkana, Kitwe) • total digests • ICP analyses • prevailing wind • E-SE to W-NW

  10. Spatial distribution of metals/metalloids Co As Ettler et al. (2011) Geoderma 164, 73.

  11. 0-5 cm Vertical distribution of metals/metalloids Oxisol – Rhodic Haplustox topsoil TOC 7 wt.% ppm Soil mineralogy: quartz, clays (kaolinite), hematite

  12. Chemical fractionation (SEP)

  13. Tracing the pollution (3-isotope plot)

  14. Spatial Pb distribution (bulk/isotopes) Pb 206Pb/207Pb Ettler et al. (2011) Geoderma 164, 73.

  15. Pb isotopes and SEP fractions 80 ppm Pb < 50 ppb 1 ppm • residual fraction – background 206Pb/207Pb signature (~ 1.35) • reducible fraction (Fe oxides) – mixture of natural and anthropogenic Pb • minute fraction of Pb bound in mobile forms in deeper soil horizons

  16. Bioaccessibility - health implications • soil ingestion • 200 mg soil per day • more critical for children • pica behaviour (up to 10 g/day)

  17. Polluted topsoils in the Copperbelt mining area (n = 52) max. content (mg/kg): Cu 27410 Co 606 Pb 480 Zn 450 As 255 smelting area (n = 55)

  18. Simple Bioaccessibility Extraction Test (SBET) • 0.4 M glycine, pH 1.5 (HCl) – gastric fluid simulation Bioaccessibility: As, Pb (81-100%) Co, Cu, Zn (58-83 %) Ettler et al. (2012) J. Geochem. Explor.113, 68.

  19. Ecotoxicological implications • calculated for a child (10 kg) • daily intake of 100 mg soil • ingested TDI tolerable daily limit • (µg/day) (µg/day) • As 6.77 10 • Co 36.5 14 • Cu 1710 1400 • Pb 34.2 36 • Zn 22.5 5000 Ettler et al. (2012) J. Geochem. Explor.113, 68.

  20. Conclusions and implications • spatial distribution of metallic/metalloid pollution • corresponds to fall-out of the dust from the Nkana • smelter chimney • extreme contamination (Cu > 3.7 wt.%) • remains in the uppermost soil horizons (0-5 cm) • indication of minute contaminant downward • leachingconfirmed by Pb isotopic tracing

  21. Cu, Pb and As are bound in available fractions (exchangeable and reducible) • >>> bioavailability (crop contamination) • >>> slow downward leaching during the rainy • seasons • high risk for human health related to soil • ingestion

  22. Thanks for your attention! Kříbek et al. (2010) J. Geochem. Explor.104, 69. Vítková, Ettler et al. (2010) Mineral. Mag.74, 581. Vítková, Ettler et al. (2011) Appl. Geochem.26, S263. Ettler et al. (2011) Geoderma 164, 73. Ettler et al. (2012) J. Geochem. Explor.113, 68.

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