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
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…)
Cu-Co mining and smelting
(Copperbelt province, Zambia)
• 30 Mt Cu produced since 1930s
• average ore grade
• 3 wt.% Cu
• 0.18 wt.% Co
Screening environmental study
• topsoils/subsurface
• maximum values
Cu 41900 ppm
Co 606 ppm
Pb 503 ppm
Zn 450 ppm
As 255 ppm
Nkana
smelter
Co, Cu – smelter emissions
Pb, Zn, As - slags related
Cr, Ni – bedrock related
Kříbek et al. (2010) J. Geochem. Explor. 104, 69-86
Nkana smelter (Kitwe)
• in operation 1930-2009
Nkana smelter - view from N
Copperbelt smelter emissions
• dust fallout – high metals
Cu 20170 ppm
Co 1542 ppm
Cu sulphide
TEM
• Cu-bearing phases
(TEM, XRD)
chalcanthite (CuSO4·5H2O)
delafossite (CuFeO2)
Cu-(Fe) sulphides
Cu sulphate
Vítková, Ettler et al. (unpublished data)
Vítková et al. (2011) Appl. Geochem. 26, S263
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.
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?
Spatial distribution of metals
Cu
• 192 topsoils
(Nkana, Kitwe)
• total digests
• ICP analyses
• prevailing wind
E-SE to W-NW
highly polluted
soil profile
110-cm-deep
Spatial distribution of metals/metalloids
Co
As
Ettler et al. (2011) Geoderma 164, 73.
Vertical distribution of metals/metalloids
Oxisol – Rhodic Haplustox
0-5 cm
topsoil TOC
7 wt.%
ppm
Soil mineralogy:
quartz, clays (kaolinite), hematite
Chemical fractionation (SEP)
Tracing the pollution (3-isotope plot)
Spatial Pb distribution (bulk/isotopes)
Pb
206Pb/207Pb
Ettler et al. (2011) Geoderma 164, 73.
Pb isotopes and SEP fractions
< 50 ppb
1 ppm
80 ppm Pb
• 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
Bioaccessibility - health implications
• soil ingestion
• 200 mg soil per day
• more critical for children
• pica behaviour (up to 10 g/day)
Polluted topsoils in the Copperbelt
mining area (n = 52)
max. content
(mg/kg):
smelting area (n = 55)
Cu 27410
Co 606
Pb 480
Zn 450
As 255
• 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.
Ecotoxicological implications
• calculated for a child (10 kg)
• daily intake of 100 mg soil
As
Co
Cu
Pb
Zn
ingested
(µg/day)
TDI tolerable daily limit
(µg/day)
6.77
36.5
1710
34.2
22.5
10
14
1400
36
5000
Ettler et al. (2012) J. Geochem. Explor. 113, 68.
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
leaching confirmed by Pb isotopic tracing
• 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
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.