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Geochemical Weathering Increases Lead Bioaccessibility in Semi-Arid Mine Tailings
journal contribution
posted on 2012-06-05, 00:00 authored by Sarah
M. Hayes, Sam M. Webb, John R. Bargar, Peggy A. O’Day, Raina M. Maier, Jon ChoroverMine tailings can host elevated concentrations of toxic
metal(loid)s
that represent a significant hazard to surrounding communities and
ecosystems. Eolian transport, capable of translocating small (micrometer-sized)
particles, can be the dominant mechanism of toxic metal dispersion
in arid or semiarid landscapes. Human exposure to metals can then
occur via direct inhalation or ingestion of particulates. The fact
that measured doses of total lead (Pb) in geomedia correlate poorly
with blood Pb levels highlights a need to better resolve the precise
distribution of molecularly speciated metal-bearing phases in the
complex particle mixtures. Species distribution controls bioaccessibility,
thereby directly impacting health risk. This study seeks to correlate
Pb-containing particle size and mineral composition with lability
and bioaccessibility in mine tailings subjected to weathering in a
semiarid environment. We employed X-ray absorption spectroscopy (XAS)
and X-ray fluorescence (XRF), coupled with sequential chemical extractions,
to study Pb speciation in tailings from the semiarid Arizona Klondyke
State Superfund Site. Representative samples ranging in pH from 2.6
to 5.4 were selected for in-depth study of Pb solid-phase speciation.
The principle lead-bearing phase was plumbojarosite (PbFe6(SO4)4(OH)12), but anglesite (PbSO4) and iron oxide-sorbed Pb were also observed. Anglesite,
the most bioavailable mineral species of lead identified in this study,
was enriched in surficial tailings samples, where Pb concentrations
in the clay size fraction were 2–3 times higher by mass relative
to bulk. A mobile and bioaccessible Pb phase accumulates in surficial
tailings, with a corresponding increase in risk of human exposure
to atmospheric particles.
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Keywords
surficial tailings samplessurficial tailingsstudy Pb speciationparticle mixturesXASHuman exposurebioaccessible Pb phaseGeochemical Weathering IncreasesXRFEolian transportblood Pb levelsArizona Klondyke State Superfund Sitesequential chemical extractionsmineral compositionimpacting health riskspecies distribution controls bioaccessibilitybioavailable mineral speciesmetal dispersionPb concentrationsrepresentative samplesclay size fractionmine tailings
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