Direct Determination of Lead Speciation in Contaminated Soils by EXAFS Spectroscopy

Abstract

Direct determination of the chemical form of trace metals in soils still remains a challenge for instrumental analytical techniques. This paper examines the potential of EXAFS spectroscopy to speciate and quantify the form of trace metals in the solid fraction of soil materials using lead as a case study. Three soils contaminated by different sorts of industrial activities, including the synthesis of lead organometallics for gasoline antiknocks, Pb-Zn smelting, and recycling of lead acid battery, were investigated. In soil contaminated by alkyl-tetravalent lead compounds, lead was found to be divalent and complexed to salicylate and catechol-type functional groups of humic substances. Lead sulfate and silica-bound lead are the predominant forms in the vicinity of the battery reclamation area. Near the smelter, lead was found to be divalent and coordinated to O,OH ligands. It is present in several chemical forms, which prevented them from being identified individually. The multiplicity of lead species in soils contaminated by smelting activities is thought to be due to long-term atmospheric emissions and to the variety of lead-containing phases simultaneously, and successively, emitted in the atmosphere. EXAFS can be applied to a wide variety of matrices including sediments, solid and liquid wastes, and fly ash particles.

Organic acids enhance the uptake of lead by wheat roots

“…The coordination number for root samples was particularly low compared to that of Pb(CH 3 COO) 2 Á3H 2 O because of the high structure disorder of the Pb coordination shells in root samples. Similar observations for Pb-O coordination have been reported for organic macromolecules such as humic acids, fulvic acids or salicylate in soils (e.g., Manceau et al 1996), for lichen cells exudates such as oxalate and parietinic acid (Sarret et al 1998), and for lignocellulosic biomaterial (Dupont et al 2002).…”

“…Being one of the most frequently encountered metal contaminants in many agricultural and industrial areas, the environmental fate of Pb and its uptake by plants has been the subject of much research (Manceau et al 1996;Wu et al 1999). Because of its limited solubility due to the formation of insoluble precipitates, bioavailable levels of Pb in soils are generally low compared to other heavy metals, thus making it difficult to apply phytoremediation techniques to Pb-contaminated soils.…”

Effect of lead on the sorption of 2,4,6-trichlorophenol on soil and peat

“…In fact, the hydroxyl group of 2,4,6-TCP permits orientational interactions with H-bonding sites on soil organic matter and clay surfaces (Boyd, 1982). However, lead also can bind to these groups (Manceau et al, 1996). The overlapping of adsorption sites implies that lead may suppress the sorption of 2,4,6-TCP on these groups of organic matter and clay minerals.…”

“…At low concentrations, lead is adsorbed at the specific adsorption sites. Manceau et al (1996) observed that lead adsorbed in soils tends to form inner-sphere complexes, in which lead is coordinated with hydroxyl functional moieties from soil particles (clay mineral and soil organic matter) (Xia et al, 1997).…”

Peer Reviewed: Reducing Children's Risk from Lead in Soil

“…Additionally, scanning electron microscopy and energy-dispersive X-ray and Xray adsorption fine structure (XAFS) analyses have been used to characterize the reaction product and forms of lead in contaminated soils (33,44,45).…”