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(NAS Colloquium) Geology, Mineralogy, and Human Welfare (1999) / Chapter Skim
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Contaminant Bioavailability in Soils, Sediments, and Aquatic Environments
Pages 3365-3371

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From page 3365...
... Whereas adsorbed Pb can be comparatively inert, the lead oxides, sulfates, and carbonates are all highly soluble in acidic to circumneutral environments, and soil Pb in these forms can pose a significant environmental risk. In contrast, the lead phosphates [e.g., pyromorphite, Pb5(PO4~3Cll are much less soluble and geochemically stable over a wide pH range.
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From page 3366...
... Concomitantly, recognition that bioavailability can be tied to solubility rather than total concentration allows one to consider remediation strategies based on in situ reductions solubility of a contaminant, rather than its complete removal. Solubility and the Solubility Product The assertion that the bioavailability of a given element in soils or sediments is controlled by its solid-phase form rests on the assumption that uptake of a contaminant by a target organism happens through the solution phase.
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From page 3367...
... Litharge Anglesite Cerussite Pyromorphite Hydroxypyromorphite Fluoropyromorphite Bromopyromorphite Corkite Hindsalite Plumbogummite PbO PbSO4 PbCO3 Pbs(PO4~3C1 Pb5(PO4~30H Pbs(PO4~3F Pbs(PO4~3Br PbFe3(PO4)
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From page 3368...
... , pyromorphite can nucleate homogeneously as a result of interactions between dissolved Pb and phosphate (50, 51~. In situ, AFM measurements of Pb solutions reacting with hydroxylapatite particles, showed only "clean" apatite surfaces without coatings of pyromorphite crystals (51~.
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From page 3369...
... In these experiments, the Pb-treated goethites and the apatite particles were separated by dialysis membranes. Hexagonal pyromorphite crystals formed on the inside surfaces of the dialysis membranes, indicating that nucleation on the apatite surface is not required for pyromorphite precipitation as was also suggested by Lower and coworkers (50, 51~.
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From page 3370...
... Many of these efforts involve the formation of geochemically stable solids through precipitation and/or adsorption reactions. In essence, these methods attempt to close the circle, converting labile forms of toxic elements into less reactive solids more consistent with long-term geochemical equilibrium.
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From page 3371...
... Colloquium Paper: Traina and Laperche 25. Santillan-Medrano, J
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Key Terms

  • solubility product
  • pyromorphite crystals
  • total concentration
  • dissolution rates
  • aquatic environments

  • apatite particles
  • geochemically stable
  • chemical lability
  • toxic elements
  • highly soluble

  • root surfaces
  • solution phase
  • toxic metals
  • scanning electron
  • metal ions

  • solubility products
  • pyromorphite precipitation
  • toxic solid
  • constituent ions
  • intrinsically low

  • hydrolytic species
  • natural fluorapatites
  • crystals formed
  • xrd peaks
  • remove toxic

  • synthetic hydroxylapatite
  • adsorption reactions
  • apatite amendments
  • similar particles
  • solid solutions


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