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.
River basin metal pollution originates from heavy industries (plating, automobile) and from urban sources (Paris conurbation: 2740 km(2), 9.47 million inhabitants). The natural sources of metal have been found to be limited due to sedimentary nature of this catchment and to the very low river sediment transport (10 t km(-2) y(-1)). Several types of data have been collected to build the metal budget within the whole Seine River basin: field surveys, economical statistics and environmental models. Environmental contamination and related fluxes have been measured on atmospheric fallout, rural streams particles, and Seine River particles upstream and downstream of Paris and at river mouth. Metal pathways and budgets have been set up for (i) a typical cultivated area, (ii) a Paris combined sewer system, (iii) Paris conurbation and (iv) the whole catchment metal retention effect in floodplain and dredged material. Metal fluxes to the estuary have been decomposed into natural, urban domestic and other sources. The latter are within 1-2 orders of magnitude larger than waste water fluxes directly released into rivers according to an industrial census. These fluxes have been further compared to the annual use (1994-2003) of these metals. Metal excess fluxes exported by the river are now a marginal leak of metal inputs to the catchment (i.e. "raw" metals, metals in goods, atmospheric fallout), generally from 0.2 to 5 per thousand. However, due to the very limited dilution power in this basin, the contamination of particles is still relatively high. The Seine River basin is gradually storing metals, mostly in manufactured products used in construction, but also in various waste dumps, industrial soils, agricultural and flood plain soils.
Kinetic EDTA and citrate extractions were used to mimic metal mobilization in a soil contaminated by metallurgical fallout. Modeling of metal removal rates vs. time distinguished two metal pools: readily labile (QM1) and less labile (QM2). In citrate extractions, total extractability (QM1+QM2) of Zn and Cd was proportionally higher than for Pb and Cu. Proportions of Pb and Cu extracted with EDTA were three times higher than when using citrate. We observed similar QM1/QM2 ratios for Zn and Cu regardless of the extractant, suggesting comparable binding energies to soil constituents. However, for Pb and Cd, more heterogeneous binding energies were hypothesized to explain different kinetic extraction behaviors. Proportions of citrate-labile metals were found consistent with their short-term, in-situ mobility assessed in the studied soil, i.e., metal amount released in the soil solution or extracted by cultivated plants. Kinetic EDTA extractions were hypothesized to be more predictive for long-term metal migration with depth.
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