Lead Speciation and Association with Organic Matter in Various Particle-Size Fractions of Contaminated Soils

Abstract

Lead (Pb) stabilization in polluted soils treated by a Pb immobilization technique may be dependent on the speciation of Pb present in specific particle-size fractions of the soil. However, the scale-dependency of Pb speciation in contaminated soils is still not clearly understood. In this study, the natures and amounts of Pb chemical forms were determined in five Pb-polluted soil samples from Klity Village, Thailand, and their particle-size fractions. This was achieved using multiple analytical tools, including bulk extended X-ray absorption fine structure (EXAFS) spectroscopy at the Pb LIII edge. Results suggested that cerussite, Pb sorbed to goethite, and Pb-humate were present in specific amounts in all bulk samples and their particle-size fractions. The highest amounts of Pb-humate were found in the smallest particles of the soil samples. This Pb form was present in the fine particles of a soil sample, but remained undetected when analyzing the bulk sample. Since Pb-SOM association may impede the formation of pyromorphite in soils, the results implied that the extent of Pb immobilization in a polluted soil treated by P may be less than predicted if Pb speciation is only characterized at the macroscopic scale from the bulk soil sample prior remediation.

Long-Term in Situ Reduction in Soil Lead Bioavailability Measured in a Mouse Model

“…Estimates of RBA > 1 suggest that the soil contained a Pb species that was more bioavailable than Pb 2+ produced from dissociation of lead acetate, the soluble reference Pb compound. RBAs > 1 have been reported from swine studies of soils enriched with highly soluble lead carbonate . However, as noted below, there was no evidence of lead carbonate or other highly soluble forms of Pb in the diets that were amended with soil and fed to mice.…”

“…RBAs > 1 have been reported from swine studies of soils enriched with highly soluble lead carbonate. 41 However, as noted below, there was no evidence of lead carbonate or other highly soluble forms of Pb in the diets that were amended with soil and fed to mice.…”

“…Additional studies involving repeated sampling of remediated sites will be needed to characterize the time dependence of such changes. Differences in inorganic and organic components of soils that affect formation of insoluble Pb–P species and the efficacy of soil remediation procedures also require additional study. , Determination of soil Pb RBA in the mouse gives a direct measure of the efficacy of treatment that can be coupled with determination of Pb speciation in treated soil to provide insights into the design of more effective soil-specific remediation processes.…”

Long-Term Biosolids Application on Land: Beneficial Recycling of Nutrients or Eutrophication of Agroecosystems?

“…The observation that extractable Pb did not appear to increase as a result of biosolids application despite an increase in total soil Pb can be attributed to the greater organic matter content and higher pH of the amended soils (Table 2). The strong affinity of organic matter in soils for Pb [37,38] is likely to have prevented measurable increases in Pb extractability. The Modified Morgan extractable P test results (Table 4) revealed extreme excesses of bioavailable P (as high as 687 mg kg −1 P) in the biosolids-amended soils.…”

Dual Regulatory Role of Penicillium oxalicum SL2 in Soil: Phosphorus Solubilization and Pb Stabilization

“…Nonetheless, recent research showed that the effect of PSM on Pb mobility could be further complicated due to the diversity of factors in the soil environment. For example, the decrease of soil pH promoted the dissolution of Pb, and the change of the soil microstructure affected the precipitation and adsorption process of Pb . Additionally, the introduction of new species can change the direction of the succession of soil microbial communities, and the changes in the soil microbial community structure and function may be important factors in the MIPP process. , Studies found that exogenous inoculation of PSM can increase the abundance of Pb-tolerant dominant genera and P-solubilization genes in soil, thus strengthening the P-cycling potential of indigenous microorganisms .…”