Bioaccessibility of Lead from Contaminated Soil Using Phosphate Treatment PDF Download

Author: Austin Charles Doss
Publisher:
ISBN:
Category :
Languages : en
Pages : 155

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"Phosphate treatments are used to immobilize lead in soil by forming pyromorphite. Soil from Bonne Terre, Mo was collected to study whether such treatment decreases the bioaccessibility of lead. The soil was treated using 0.5 soil wt% of phosphate. Treatments were: none, phosphoric acid, triple super phosphate, and organic bone meal. Each sample was studied after one, four, sixteen, and twenty weeks; during this time span, water was added approximating the average rainfall rate. Percolated water was collected to test the leached phosphate concentrations. Phosphate was below the detection limit in that leachate. Remediated soil samples were used in Physiologically Based Extraction Tests (PBET) and In Vitro Gastrointestinal Method Tests (IVG). Lead concentrations were determined using Flame Atomic Adsorption (FAA) and Graphite Furnace Atomic Adsorption (GFAA). Titrations of synthetically formed chloropyromorphite were conducted to determine the effect of pH on the dissolution of chloropyromorphite. Results showed that as pH decreased, dissolution between lead and phosphate increased. Ksp's of chloropyromorphite ranged from 10[sup -33.3] to 10[sup -84.4] depending on the varying pH and phosphate source. Remediated soil samples were used in a density separation analysis to determine heavy metal composition. Lead compounds such as lead sulfide, lead oxide and lead dioxide were found in trace amounts. The adsorption rate of lead through the stomach lining has been considered but not analyzed throughout this research. A decrease in lead bioaccessibility was observed after a remediation period of 20 weeks"--Abstract, page iii.

Author: Martina Laura Vázquez Miranda
Publisher:
ISBN:
Category : In situ remediation
Languages : en
Pages : 107

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Lead (Pb) speciation in soil is key for bioavailability assessment and exposure risk to humans from Pb contaminated soils. Soil ingestion is the main exposure pathway in Pb contaminated soils and in vitro bioaccessibility assays (IVBA) can predict relative bioavailable (RBA) Pb in soil by mimicking the GI tract conditions without traditional expensive animal feeding studies. In situ soil remediation has been considered an effective ecological treatment option compared to ex-situ techniques. The use of amendments such as biosolids, biochar, compost and phosphorous (P) amendments have been effective to decrease RBA in soils and, in doing so, reducing human exposure to the contaminant. In this study, soil amendments including biosolids, compost, wood-ash, biochar, soluble phosphate (SP) and their combinations were applied to Pb contaminated soil. Soil samples were incubated for up to 6 months at constant temperature, moisture and humidity. Samples were taken at three time points 1 (t1), 4 (t2) and 6 (t3) months of incubation and analyzed for total metal content, bioaccessible Pb (%IVBA-Pb), bioaccessible arsenic (%IVBA-As), organic carbon content (Org C), pH, extractable P and other key properties to determine the best treatment to reduce bioavailability of lead while improving soil health. Phosphorous was the most effective amendment to reduce %IVBA-Pb. Whether as individual or combined amendments, SP and biosolids resulted in 25-50% reductions of %IVBA Pb. Organic C addition did not reduce %IVBA-Pb, indicating complexation was not relevant for chemical immobilization of Pb in the case of strongly acidic soils such as the ones used in this experiment. %IVBA-As was correlated with pH and not P addition nor Organic C addition. Biosolid addition produced, apart from an expected plant available P increase, a great increase in Mineralizable Nitrogen content in the soils. Considering the importance of Nitrogen as an essential nutrient in plant growth, these results indicate that this amendment would be suitable for decreasing %IVBA-Pb and overall exposure to Pb contaminated soils. This is due to ensuring plant cover in the soils and decreasing soil erosion and loss, with the subsequent Pb dust dispersion, decreasing possible ingestion rates of the soil.

Author: Samantha Jo DiCenso
Publisher:
ISBN:
Category :
Languages : en
Pages : 136

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"Lead is known to cause health problems in humans, especially children, and an effective in-situ remediation option has been sought for years. Adding phosphoric acid (PA) to contaminated soil causes a reaction that binds the lead to phosphate to produce pyromorphite (Pb5(PO4)3Cl), a form of lead believed to be non-bioavailable; however, field trials have given varied results (Bosso et al 2008; Munksgaard and Lottermoser 2011; Tang et al. 2009). One explanation for these results might be the impact of the agent used to raise pH after phosphoric acid addition. In order to examine this explanation soil was collected from the Bonne Terre area in Missouri, which is known to have a high lead content due to past smelting activities. The soil was mixed with PA before calcium hydroxide and sodium hydroxide were added to the soil to neutralize the pH changes caused by the PA addition, and to determine whether the pH amendment impacted the rate of pyromorphite formation. The soil was then run through a physiologically-based extraction test (PBET) that simulates a child's stomach process to evaluate the success of the remediation attempt. The soil was monitored for a month after amendment addition, with all soil samples run through the PBET and a flame atomic absorption spectrometer to analyze the samples. Upon discovering that the change in concentration of extractable lead in soil was not statistically significant, an invitro test was conducted to discover what was occurring in the soil. Titration experiments were conducted based on the idea that pyromorphite was forming in the soil, but the low stomach pH was causing it to re-dissolve. The titration experiments showed that below pH 3, pyromorphite dissolves, a hitherto overlooked phenomenon"--Abstract, page iii.

Author:
Publisher:
ISBN:
Category : Lead abatement
Languages : en
Pages : 8

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Author: Tang, Xi
Publisher:
ISBN:
Category : Electronic dissertations
Languages : en
Pages :

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In situ application of soluble phosphates and organic matter is considered to be a cost effective remediation technique for immobilizing lead (Pb) and other heavy metals and reducing health and ecological risks associated with contaminated soils. However, a longterm assessment of risk reduction induced by metal immobilization is needed to verify efficacy and gain regulatory and public acceptance of phosphate-based and organic matter-based remedial technologies. The study sites included a smelter-contaminated urban site, a mill-waste contaminated site, and a mining-waste contaminated site within the Jasper County Superfund Site, Southwestern Missouri. Field plots at the urban site were treated with phosphoric acid at a rate of 10 g kg−1 using surface application (SA), rototilling (RT), and pressure injection (PI); plots at the mill-waste site were treated with phosphoric acid at rates of 7.5 and 10 g kg−1 and incorporated using rototilling; plots at the mining-waste site were treated with different types of organic amendments, including biosolids and agricultural byproducts. The parameters chosen to assess long-term risk reduction were: (1) metal bioavailability to organisms; (2) metal availability to plants (i.e., phytoavailability); (3) toxicity of treated soils to microorganisms; (4) phosphate and metal stability; and (5) solid phase P and Pb speciation assessed using microscopic, spectroscopic, and chemical fractionation techniques. Results demonstrated that most of the phosphoric acid and OM treatments significantly reduced bioavailability, phytoavailability, and leachability of metals (Pb and Cd) in the contaminated soil. Analysis of P and Pb fractionation confirmed these reductions as well. In addition, most of treatments did not significantly impact toxicity in the soil to microorganisms. Thus, the in situ remediation of metal contaminated soil using phosphoric acid and OM is considered to be a practical remediation strategy with longterm benefits.

Author: Manfred M. Mayer
Publisher:
ISBN:
Category : Lead
Languages : en
Pages : 0

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Measuring the reduction of in vitro bioaccessible (IVBA) Pb from the addition of phosphate amendments has been researched for more than two decades. The mean change in IVBA Pb as a fraction of total Pb (AC) and relative to the IVBA Pb of the control soil (RC) was determined with a random effects meta-analysis. The addition of P to contaminated soils consistently reduced IVBA Pb. The mean AC was approximately -12% and mean RC was approximately -25% based on 76 soils that measured IVBA Pb with a method other than EPA Method 1340. This analysis determined that soluble amendments reduce bioaccessible Pb more than insoluble amendments, phosphoric acid is more effective than other phosphate amendments, and urban Pb contamination, associated with legacy Pb-paint and tetraethyl Pb, showed lower reductions than other Pb sources. Meta-regression identified high IVBA Pb in the control, low incubated soil pH, and high total Pb with the greater reductions in AC and RC. In order to facilitate comparisons across future remediation research, a set of minimum reported data should be included in published studies and researchers should use standardized in vitro bioaccessibility methods developed for P-treated soils. Meta-analysis identified lowered incubated soil pH as correlated with greater reductions in IVBA Pb but previous studies have found purposeful acidification to have no significant effect on IVBA Pb. In this study, three soils (IDs: AG, TH, SA), previously incubated with triple superphosphate, were acidified to pH 3 with 6M trace-metal grade HCl, and subsequently neutralized with 6M NaOH, to determine if acidification of soil influences IVBA Pb in soils amended with phosphate. The acidification of soil took varying amounts of HCl and markedly less 6M NaOH to return soils to initial pH. The treatment effect ratios (TER) for acidification and neutralization varied by soil. No significant differences were observed for any treatment in SA soil. The acidified treatments had significantly lower bioaccessible Pb for the other two soils with a TER of 0.52 for TH soil and 0.70 for AG soil. Only TH soil had a neutralized treatment which was significantly lower than the control (TER of 0.76). Importantly, no increase in bioaccessible Pb was observed in any soil implying no increased risk from soil acidification. Further primary research is needed to determine the relationship between different soil properties and reduction in bioaccessible Pb attributable to the addition of P amendments.

Author: H. Magdi Selim
Publisher: CRC Press
ISBN: 148223680X
Category : Nature
Languages : en
Pages : 381

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Edited by One of the Best Specialists in Soil Science Recent studies reveal that Phosphorus (P) in the form of phosphate, a macronutrient essential for plant growth, and crop yields can influence the bioavailability, retention, and mobility of trace elements, metal(loid)s, and radio nuclides in soils. When this occurs, phosphates can affect the dynamics of heavy metals and influence soil characteristics, impacting soil mobility and toxicity. Phosphate in Soils: Interaction with Micronutrients, Radionuclides and Heavy Metals utilizes the latest research to emphasize the role that phosphate plays in enhancing or reducing the mobility of heavy metals in soil, and the soil-water-plant environment. It provides an in-depth understanding of each heavy metal species, and expands on phosphate interactions in geological material. Composed of 12 chapters, this text: Provides an overview of the reactions of metal(loid)s and common P compounds that are used as fertilizer in soils Emphasizes the effect of phosphorus on copper and zinc adsorption in acid soils Discusses findings on the influence of phosphate compounds on speciation, mobility, and bioavailability of heavy metals in soils as well as the role of phosphates on in situ and phytoremediation of heavy metals for contaminated soils Places emphasis on the influence of phosphate on various heavy metals species in soils, and their solubility/mobility and availability Provides extensive information on testing various high phosphate materials for remediation of heavy metal, micronutrients, and radionuclides contaminated sites Explores the reactivity of heavy metals, micronutrients and radionuclides elements in several soils Presents a case study illustrating various remediation efforts of acidic soils and remediation of Cu, Zn, and lead (Pb) contaminated soils around nonferrous industrial plants Emphasizes the significance of common ions (cations and anions) on phosphate mobility and sorption in soils, and more The author includes analytical and numerical solutions along with hands-on applications, and addresses other topics that include the transport and sorption modeling of heavy metals in the presence of phosphate at different scales in the vadose zone.

Author: Xinde Cao
Publisher:
ISBN:
Category : Lead
Languages : en
Pages : 112

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Lab tests and a field demonstration were conducted to evaluate the feasibility and effectiveness of immobilizing metals in contaminated soils using phosphate. Phosphate was more effective for Pb immobilization than for Zn, Cu, and Cd. The formation of insoluble pyromorphite-like minerals was responsible for Pb immobilization, whereas Zn, Cu, and Cd immobilization may be attributed to the coprecipitation and surface complexation mechanisms. The most efficient formation of pyromorphite-like minerals was found at pH 3 and at an application rate of 4 P/Pb. Soil acidification was necessary to dissolve soil Pb carbonates and to make them readily available for the formation of pyromorphite-like minerals. Therefore, a two-step phosphate amendment was applied at a contaminated site in which the soil was first acidified with H3PO4, and Ca(H2PO4)2 or phosphate rock was then added. Phosphate effectively induced transformation of soil Pb from the non-residual to the residual fraction, with residual Pb increase by up to 55%. Modeling indicated that lead phosphate minerals controlled Pb2+ activities in the P-treated soils. Phosphate treatments significantly reduced Pb uptake by Stenotaphrum secundatum. A mixture of H3PO4 and phosphate rock yielded the best overall results for in situ Pb immobilization, with less soil pH change and less phosphorus leaching.

Author: Zafer Saad Alasmary
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Potentially toxic substances can contaminate extensive areas of productive land due to military activities. The most common and widespread metal contaminant in military lands is lead (Pb). The main objectives of this study were to evaluate the feasibility of using Miscanthus, a second-generation biofuel crop, for photostabilization of Pb in contaminated military site soils; the effect of soil amendments on Miscanthus growth; and the effects of continual plant growth, nutrient removal and the soil chemical changes induced by Miscanthus growth on soil Pb bioaccessibility. In 2016, we established a field site on a US Army reservation in Fort Riley, KS. Miscanthus was planted in an area with soil total Pb concentration ranging from 900 - 1,500 mg kg−1 and near-neutral soil pH. Five treatments were evaluated: (i) control plots without tillage with existing vegetation, (ii) no-tillage, no additional amendments planted with Miscanthus, (iii) tilled soil, no additional amendments planted with Miscanthus, (iv) tilled soil amended with triple superphosphate (at 5:3 Pb:P molar ratio) planted with Miscanthus, and (v) tilled soil amended with organic P source (class B biosolids applied at 45 Mg/ha ) planted with Miscanthus. Results from three years show that one-time addition of soil amendments to Pb-contaminated soil supports establishing and stabilizing Miscanthus, increasing biomass yield as well as reducing phytoavailability and bioaccessibility of Pb. Plots amended with biosolids had significantly less total Pb uptake, plant tissue Pb concentration, and Pb bioaccessibility, and more soil enzyme activities, organic carbon, and microbial biomass. Controlled-environment greenhouse and laboratory incubation studies were conducted to test selected additional P sources. Additional sources included non-traditional, less soluble types such as struvite and apatite. The greenhouse study aimed to evaluate the effect of Miscanthus growth on bioaccessibility of amended and non-amended soils and the effect of soil amendments on soil-plant transfer of soil Pb over three Miscanthus cuttings. Soil amendments increased dry matter yield in the first cutting. Soils in Miscanthus pots that were amended with biosolids, had significantly lower total Pb uptake, Pb concentration in plant tissues, and Pb bioaccessibility when compared to the control across all cuttings. Overall, the results suggested that Miscanthus can be effectively and safely grown on Pb-contaminated soils amended with biosolids. The incubation study evaluated the effectiveness of various in situ P treatments on reducing Pb bioaccessibility and the effects of different P sources on the speciation of soil Pb over time. X-ray absorption spectroscopy was used to understand treatment-induced changes to soil Pb speciation. Results showed that soil pH decreased slightly for all treatments. Percent of bioaccessible Pb in soils amended with biosolid were significantly ([alpha]=0.05) less than the other amendments. The high rate of biosolids (225 Mg ha−1) was the most effective in controlling the bioaccessibility of soil Pb, and the reductions in bioaccessibility ranged from 63 to 76% compared to the control. X-ray absorption spectroscopy results indicated pyromorphite (stable Pb phosphates) phases were the most dominant Pb species in both amended and non-amended soils. The results of these studies suggest that Miscanthus can be grown successfully in Pb-contaminated shooting range soils in combination with organic or inorganic phosphate amendments, while minimizing the associated environmental risks.

Author: Arun S. Wagh
Publisher: Elsevier
ISBN: 9780080445052
Category : Technology & Engineering
Languages : en
Pages : 283

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The first chemically bonded phosphate ceramics (zinc phosphate dental cements) were developed over a century ago. However it has only been in the last 30 years that a new breed of materials has been discovered. This book brings together latest developments in this field including several novel ceramics, from Argonne and Brookhaven National Laboratories. Coupled with further advances in their use as biomaterials, these materials have found uses in diverse fields in recent years. Applications range from advanced structural materials to oil-well cements and stabilization and encapsulation of hazardous and radioactive waste. Such developments call a single source for their science and applications. This book provides the first comprehensive account to fulfil this need. · Providing a foundation into the latest developments in chemically bonded phosphate ceramics. · Explores new CBPC's with a wide range of practical applications. · Over 30 years worth of developments and applications in the field available in a single source