Contaminant bioavailability in soils, sediments, and aquatic environments

Abstract

The aqueous concentrations of heavy metals in soils, sediments, and aquatic environments frequently are controlled by the dissolution and precipitation of discrete mineral phases. Contaminant uptake by organisms as well as contaminant transport in natural systems typically occurs through the solution phase. Thus, the thermodynamic solubility of contaminant-containing minerals in these environments can directly inf luence the chemical reactivity, transport, and ecotoxicity of their constituent ions. In many cases, Pb-contaminated soils and sediments contain the minerals anglesite (PbSO 4 ), cerussite (PbCO 3 ), and various lead oxides (e.g., litharge, PbO) as well as Pb 2؉ adsorbed to Fe and Mn (hydr)oxides. 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, Pb 5 (PO 4 ) 3 Cl] are much less soluble and geochemically stable over a wide pH range. Application of soluble or solid-phase phosphates (i.e., apatites) to contaminated soils and sediments induces the dissolution of the ''native'' Pb minerals, the desorption of Pb adsorbed by hydrous metal oxides, and the subsequent formation of pyromorphites in situ. This process results in decreases in the chemical lability and bioavailability of the Pb without its removal from the contaminated media. This and analogous approaches may be useful strategies for remediating contaminated soils and sediments.

Immobilization of lead in shooting range soils by means of cement, quicklime, and phosphate amendments

“…Instead, PbHPO 4 formation was detected. Although the solubility product of PbHPO 4 (Ksp=10 -23.8 ) is higher than that of pyromorphite-like minerals (Ksp=10 -71.6 -10 -84.4 ), it is still much lower than that of cerussite (Ksp=10 -12.8 ) (Traina & Laperche 1999). Therefore, PbHPO 4 formation would be responsible for the reduction of Pb leachability.…”

Effect of phosphate on the adsorption of Cu and Cd on natural hematite

“…Phosphate in soil may affect the chemical reactions of metals on mineral surfaces. Recent studies (Traina and Laperche, 1999;Cao et al, 2002) indicated that phosphate minerals, such as apatite, could sequester heavy metals, metalloids and radionuclide through adsorption and/or the formation of secondary PO 3À 4 precipitates, which remained stable under a wide range of geochemical conditions. Therefore, it is necessary to examine the influence of phosphate on the reactions of heavy metals on the surface of soil minerals.…”

Developments in Bioremediation of Soils and Sediments Polluted with Metals and Radionuclides. 3. Influence of Chemical Speciation and Bioavailability on Contaminants Immobilization/Mobilization Bio-processes

“…The potential values of common soil amendments (phosphates, lime, biosolids and coal ash) relative to their ability to immobilize metals such as lead in soil or sediment are discussed by Traina & Laperche (1999), for attenuation of Cd and Zn availability in polluted soil amended with CaCO 3 and KH 2 PO 4 (Hamon et al 2002), for Pb, Cd, As and Hg immobilization with phosphates and lime (Porter et al 2004). For the review of the implications of liming in relation to heavy metal transformation and bioavailability in acidic soils see Bolan et al (2003a) and Adriano et al (2004).…”