10 research outputs found
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Investigation of Lead Hydrolytic Polymerization and Interactions with Organic Ligands in the Soil/Sediment-Water Environment
The objective of this research was to investigate lead speciation in the soil/sediment-water environment and to better understand how the species affect lead mobility under different environmental conditions. The research involved both field soil and sediment samples as well as standard lead solutions. Field samples were fully characterized and extracted by aqueous and organic solvents. The results were compared and evaluated with the metal speciation model, MINTEQA2. Hydrolytic polymerization and organic complexation studies were conducted with standard lead solutions under controlled experimental conditions.
Results of the field samples showed that pH, dissolved cations, ionic strength, dissolved organic matter, and nature of the soil/sediment matrix play major roles in the distribution and mobility of lead (Pb) from contaminated sites. In the aqueous equilibration experiment, the magnitude of Pb2+ solubilization was in the order of pH4>pH7>pH9. The results were in good agreement with MINTEQA2 predictions. An important finding of the research is the detection of Pb polymerization species under controlled experimental conditions. At pH 5.22, Pb polymeric species were formed at rate of 0.03 per day. The role of Pb complexation with organic matter was evaluated in both field and standard samples. Different methodologies showed three types of organically bound Pb. A very small fraction of Pb, in the ppb range, was extractable from the contaminated soil by polar organic solvents. Sequential extractions show that 16.6±1.4 % of the Pb is organically complexed. Complexation of Pb with fulvic acid provided new information on the extent of Pb association with soluble organic matter.
The overall results of this research have provided new and useful information regarding Pb speciation in environmental samples. The results, in several instances, have provided verification of MINTEQA2 model's prediction. They also revealed areas of disagreement between the models prediction and the experimental results. A positive note regarding the experimental work done in the research is the verification of the mass balance in all the repeated experiments
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Use of GIS to Identify and Delineate Areas of Fluoride, Sulfate, Chloride, and Nitrate Levels in the Woodbine Aquifer, North Central Texas, in the 1950s, 1960s, 1970s, 1980s, and 1990s
ArcView and ArcInfo were used to identify and delineate areas contaminated by fluoride, sulfate, chloride, and nitrate in the Woodbine Aquifer. Water analysis data were obtained from the TWDB from the 1950s to 1990s covering 9 counties. 1990s land use data were obtained to determine the relationship with each contaminant. Spearman's rank correlation coefficients and Kruskal-Wallis tests were used to calculate relationships between variables. Land uses had little effect on distributions of contaminants. Sulfate and fluoride levels were most problematic in the aquifer. Depth and lithology controlled the distributions of each contaminant. Nitrate patterns were controlled mainly by land use rather than geology, but were below the maximum contaminant level. In general, contaminant concentrations have decreased since the 1950s
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Atrazine Monitoring and Modeling in the Lake Lavon Watershed
This report describes a study to identify the distribution and extent of areas potentially at risk for atrazine (a broad leaf weedkiller) runoff in the Lake Lavon watershed, which is a major water supply for the Dallas area. The report presents the results of the study and makes recommendations for how information can be used in a cost-effective watershed atrazine reduction strategy