Soluble Pb Research Articles

Evaluation of potentially toxic element contamination in the riparian zone of the River Sava

Contaminated sediments transported onto the river terrace during high water events can contribute significant quantities of potentially toxic elements to riparian soils. Seven trace elements (As, Cd, Cr, Cu, Ni, Pb and Zn) were analysed in the river sediment and riparian soil of the River Sava and their spatial distribution, potential toxicity and ecological risk levels were evaluated. The results showed that levels of all the trace metals were enriched to varying extents in both the sediment (As, Cr, Ni, and Pb) and soil (Ni) when compared to reference levels for sediments and European soils. Mean concentrations of trace metals in sediment and soil, apart from Pb, increased downstream in the River Sava. The similar increasing trend of these elements in sediment and soil may be explained by their increased load due to anthropogenic pressures (As, Cr, Ni, Pb and Zn in sediment and the significant accumulation of Ni in soil) and frequent periodic flooding (As, Cd, Cr, Cu, Ni and Zn in sediment and Cd in soil are influenced by both high water events and natural factors such as the geological substrate), particularly in lowland regions. In this study, soluble As, Cd, Cr, Cu and Ni fractions in sediment and soil <10% indicated their low mobility. The exceptions were readily soluble Pb and Zn in the sediment and soil at some sampling sites. In the lower reaches, levels of Pb in sediment was indicative of a medium environmental hazard, while there was a high environmental hazard in the upper reaches with the average Pb content in sediment higher than the PEL. Pollution factors for Pb in soil indicated a medium environmental hazard in the upper and middle reaches and a high environmental hazard at some sites in the lower stretches of the Sava River, although total Pb content in soil was within the range proposed for European soils.

Clay mineralogy affects the efficiency of sewage sludge in reducing lead retention of soils

Recent studies have shown the feasibility of using of sewage sludge for the remediation of heavy metal-contaminated soils. However, there are no researches to check the influence of clay mineralogy on the efficiency of the sewage sludge to remediation of contaminated soils with heavy metals. For this purpose, we use two contrasting soils: Oxisol rich in hematite and gibbsite and Inceptisol rich in kaolinite. Thermal-treated sludge was applied to Pb-contaminated soil samples and incubated for 40 days. The soil samples were submitted to seven sequential extractions: soluble-Pb, exchangeable-Pb, precipitated-Pb, organic matter-Pb, Fe and Mn oxide-Pb, gibbsite and kaolinite-Pb, and residual-Pb. The reduction of soluble Pb forms by thermal sludge application was more pronounced in the Oxisol than in the Inceptisol because of the conversion of soluble-Pb into more stable forms, such as precipitated-Pb and oxides-Pb. For Inceptisol was necessary to apply high rates of thermal sludge to reach a significant reduction in soluble-Pb contents. The addition of humic fractions in the form of thermal sludge increased the concentration of organic matter-Pb. In confined area, the use of sewage sludge to reduce the heavy metals levels in soils must be better considered, mainly in more weathered soils.

Se-Sm co-doping strategy for tuning the structural and thermoelectric properties of GeTe-PbTe based alloys

Structural design shows great impact on enhancing the thermoelectric performance of the GeTe-PbTe based materials. The Sm and Se elements are introduced to co-dope the GeTe-PbTe based alloys using a conventional solid-solution method followed by spark plasma sintering technique and thermal annealing. The Se doping can increase the solubility of Pb in the GeTe-based matrix, leading to the suppression of the segregated PbTe-based phases. The Sm–Se co-doping introduced secondary phases and twinning microstructures along with the traditional atomic-scale point defects and grain boundaries contribute to the wide-wavelength phonon scattering, leading to the reduction of lattice thermal conductivity. The co-doping strategy also shows impact on the tuning of carrier concentration and band structures for the optimization of power factor. The minimum lattice thermal conductivity reach to 0.41 Wm−1 K−1 for the sample Ge0.75Pb0.2Sm0.03Te0.7Se0.3 at 573 K, which approaches to the amorphous limit of GeTe. The maximum figure of merit ZT value can be increased to 1.03 for the sample Ge0.75Pb0.2Sm0.03Te0.5Se0.5 at 673 K, making the co-doping strategy quite attractive for further enhancing the thermoelectric performance of GeTe-PbTe based materials.

Food influence on lead relative bioavailability in contaminated soils: Mechanisms and health implications

To determine the effects of dietary constituents on soil Pb oral bioavailability, Pb relative bioavailability (RBA) in 3 soils contaminated by zinc smelting (ZS), wire-rope production (WR), and metal mining (MM) was measured under fasted and fed states with 9 foods. Under fasted state, Pb-RBA was 84.4 ± 10.3, 82.6 ± 4.70, and 32.3 ± 1.10% for ZS, WR, and MM soils; however, it decreased by 1.3–3.5 fold to 23.9–58.8, 25.6–49.9, and 14.8–24.2% under fed states with foods excluding Pb-RBA with egg in WR soil (97.3 ± 4.46%), and with cabbage and egg in MM soil (40.0 ± 8.62 and 44.4 ± 0.96%). In the presence of foods, egg and pork with significantly higher protein and fat contents leaded to the highest soil Pb-RBA (44.4–97.3%), while Pb-RBA determined with mineral-rich mouse feed was 1.6–7.9 fold lower (9.41–13.5%), suggesting high fat and protein foods tended to increase soil Pb-RBA, while high mineral diets decreased soil Pb-RBA. The increased Pb-RBA of MM soil with cabbage compared to fasted state was due to high organic content in cabbage, which could increase soil Pb solubility by inhibiting Fe and Pb co-precipitation in the intestine. For accurate assessment of health risks of contaminated soils, dietary influence on soil Pb-RBA should be considered.

Low-carbon and low-alkalinity stabilization/solidification of high-Pb contaminated soil

Stabilization/solidification (S/S) is a low-cost and time-efficient method for soil remediation, however, delayed hydration reactions and high carbon footprint are major limitations for the treatment of high-Pb contaminated soil. This study develops a novel and low-carbon approach that combines ground granulated blast furnace slag (GGBS) and ordinary Portland cement (PC) with phosphate-/sulphate-rich byproducts to produce low-alkalinity, high-compatibility, high-strength binary cement (BC) for S/S process. Results show that contaminated soil with a large fraction of exchangeable and soluble Pb (e.g., shooting range sites) severely disturbed the formation of hydration products in conventional S/S treatment, whereas BC system could mitigate the Pb interference via precipitation and sorption evenly distributed on the BC hydrates as shown by elemental mapping. Thus, BC presented superior environmental performance in terms of toxicity characteristic leaching procedure (TCLP) and semi-dynamic leaching tests, which were substantiated by quantitative X-ray diffraction and thermogravimetric analyses. The addition of potassium dihydrogen phosphate reduced TCLP leachability of Pb by 86.9% and Pb diffusion coefficients by 69.4% due to the formation of insoluble Pb3(PO4)2. Similarly, incinerated sewage sludge ash enhanced Pb stabilization, whereas waste phosphogypsum increased early strength via precipitation of PbSO4, although the effectiveness of physical encapsulation was compromised due to reduction in hydration products. Therefore, the proposed binary binders with selected additives present a new and low-carbon S/S treatment for high-Pb shooting range soil remediation.

Isolation and Characterization of Pb-Solubilizing Bacteria and Their Effects on Pb Uptake by Brassica juncea: Implications for Microbe-Assisted Phytoremediation.

The aim of this study was to isolate and characterize lead (Pb)-solubilizing bacteria from heavy metal-contaminated mine soils and to evaluate their inoculation effects on the growth and Pb absorption of Brassica juncea. The isolates were also evaluated for their plant growth-promoting characteristics as well as heavy metal and salt tolerance. A total of 171 Pb-tolerant isolates were identified, of which only 15 bacterial strains were able to produce clear haloes in solid medium containing PbO or PbCO3, indicating Pb solubilization. All of these 15 strains were also able to dissolve the Pb minerals in a liquid medium, which was accompanied by significant decreases in pH values of the medium. Based on 16S rRNA gene sequence analysis, the Pb-solubilizing strains belonged to genera Bacillus, Paenibacillus, Brevibacterium, and Staphylococcus. A majority of the Pb-solubilizing strains were able to produce indole acetic acid and siderophores to different extents. Two of the Pb-solubilizing isolates were able to solubilize inorganic phosphate as well. Some of the strains displayed tolerance to different heavy metals and to salt stress and were able to grow in a wide pH range. Inoculation with two selected Pb-solubilizing and plant growth-promoting strains, (i.e., Brevibacterium frigoritolerans YSP40 and Bacillus paralicheniformis YSP151) and their consortium enhanced the growth and Pb uptake of B. juncea plants grown in a metal-contaminated soil. The bacterial strains isolated in this study are promising candidates to develop novel microbe-assisted phytoremediation strategies for metal-contaminated soils.

Potato absorption and phytoavailability of Cd, Ni, Cu, Zn and Pb in sierozem soils amended with municipal sludge compost

Effects of sludge utilization on the mobility and phytoavailability of heavy metals in soil-plant systems have attracted broad attention in recent years. In this study, we analyzed the effects of municipal sludge compost (MSC) on the solubility and plant uptake of Cd, Ni, Cu, Zn and Pb in a soil-potato system to explore the mobility, potato plant uptake and enrichment of these five heavy metals in sierozem soils amended with MSC through a potato cultivation trial in Lanzhou University of China in 2014. Ridge regression analysis was conducted to investigate the phytoavailability of heavy metals in amended soils. Furthermore, CaCl2, CH3COONH4, CH3COOH, diethylene triamine pentacetic acid (DTPA) and ethylene diamine tetraacetic acid (EDTA) were used to extract the labile fraction of heavy metals from the amended soils. The results show that the MSC could not only improve the fertility but also increase the dissolved organic carbon (DOC) content of sierozem soils. The total concentrations and labile fraction proportions of heavy metals increase with increasing MSC percentage in sierozem soils. In amended soils, Cd has the highest solubility and mobility while Ni has the lowest solubility and mobility among the five heavy metals. The MSC increases the concentrations of heavy metals in the root, stem, peel and tuber of the potato plant, with the concentrations being much higher in the stem and root than in the peel and tuber. Among the five heavy metals, the bioconcentration factor value of Cd is the highest, while that of Ni is the lowest. The complexing agent (DTPA and EDTA) extractable fractions of heavy metals are the highest in terms of phytoavailability. Soil properties (including organic matter, pH and DOC) have important impacts on the phytoavailability of heavy metals. Our results suggest that in soil-potato systems, although the MSC may improve soil fertility, it can also increase the risk of soils exposed to heavy metals.

Study of the solubility of Pb, Bi and Sn in aluminum by mixed CALPHAD/DFT methods: Applicability to aluminum machining alloys

The aim of this work is a formulation of a thermodynamic model for the development of new aluminum machining alloys. The three additives Bi, Pb and Sn have proven to help machining. Hence, a review of the literature showed that the liquid phase equilibria and thermodynamic data for the three binary systems Al-Bi, Al-Pb and Al-Sn is very thorough but the limited information for the FCC solution required the use of Density Functional Theory (DFT) to predict thermodynamic data. The partial heat of mixing of these three machining additives in Al(FCC) are obtained and the results helped to improve the thermodynamic model using the CALPHAD method. It was shown that for all three binary systems, the thermodynamic data obtained at three fixed compositions and that obtained for a very dilute solution gave different enthalpy curves. The thermodynamic model was used to compute the ternary systems Al-Bi-Pb, Al-Bi-Sn and Al-Pb-Sn and small adjustable parameters were added to reproduce the literature data.

Ca-containing amendments to reduce the absorption and translocation of Pb in rice plants

The influence of three Ca-containing amendments (dolomite, slaked lime, and limestone) on soil water soluble Pb (Pb-w) levels, Pb accumulation by two rice plants (TJ-8, japonica and II-3301, indica), and the factors affecting Pb-w were investigated. Pot experiment was performed under waterlogged conditions using Pb-contaminated soil collected from an agricultural field near a mine. It was found that the soil amendments significantly reduced Pb content in the rice plants in the order dolomite > slaked lime > limestone, irrespective of rice cultivar. The Pb content of brown rice with the added soil amendments was lower than that of the recommended limit (0.2 mg kg−1, GB2762-2017) except for cultivar II-3301 with slaked lime. There was a significant positive correlation between the Pb content of the roots, stems, leaves, and grains and the soil Pb-w levels. The amendments reduced soil Eh, Fe, and Mn concentrations in the pore water and increased soil pH. The total organic carbon (TOC) in the pore water significantly decreased for II-3301 but not for TJ-8 at the ripening stage after addition of the amendments. Among soil Eh, pH, TOC, Fe, and Mn in the pore water, Fe and Mn were the most influential in lowering soil Pb-w levels. The amendments inhibited the formation of iron plaques on the root surface and reduced Pb adsorption. The Pb content of the roots was positively correlated with that in iron plaque. These findings are significant as they imply that the application of Ca-containing amendments in Pb-contaminated paddy soils near mines is an effective approach for in situ immobilization of Pb and reduction in Pb levels in the edible parts of crops.

Slight Symmetry Reduction in Thermoelectrics

Thermoelectric research on germanium telluride (GeTe) has been mainly focused on the enhancement of its performance in the high-temperature cubic phase since the 1960s. Recently in Joule, Pei and co-workers achieved an unprecedented thermoelectric figure of merit in rhombohedral-phase GeTe by exploiting slight symmetry breaking in the structure, which simultaneously improved the electronic properties and reduced the lattice thermal conductivity.

Point of zero charge: Role in pyromorphite formation and bioaccessibility of lead and arsenic in phosphate amended soils.

Soluble lead (Pb) can be immobilized in pure systems as pyromorphite by adding sources of phosphorus (P), but uncertainties still remain in natural systems. Knowledge of PZC is important to predict the ionization of functional groups and their interaction with metal species in solution. This study utilized the Pb- and As-contaminated soils to determine the combined effect of pH with respect to PZC and different rates of P-application on pyromorphite formation, and Pb and arsenic (As) bioaccessibility as impacted by speciation changes. Solution chemistry analysis along with synchrotron-based Pb- and As-speciation, and bioaccessibility treatment effect ratios (TERs) were conducted. Results indicated no significant effect of PZC on pyromorphite formation in P-amended soils; however, the TERPb appeared significantly lower at pH>pHPZC and higher at pH<pHPZC (α = 0.05). In contrast, the TERAs was significantly higher at pH>pHPZC, compared to the other two treatments, for the tested soils. The lack of conversion of soil Pb to pyromorphite may be attributed to presence of stable minerals limiting soluble-Pb availability and high organic matter content of the tested soils.

Effect of Organic Matter Amendment on Lead Contamination in Roadside Soil and Plant

Lad Contamination in Roadside Soil and Plant and Effect of Organic Matter Amendment (Sabaruddin, D Budianta and Mardia): Roadside soils and plants may be the most important sink of lead (Pb). It has been widely known that soil organic matter (SOM) plays important roles in determining concentrations of metals in soil solution and their extractability from the soil. To investigate Pb contamination in the roadside soils and plants, as well as the effect of organic matter (OM) on the soluble Pb in the roadside soils, surface soils (0 to 20 cm) were collected from a busy road. The soils were incubated for 4 weeks under room temperature after being treated with 0, 30, 60 and 90 Mg ha-1 of OM. Leaves of oil palms (Elaeis guineensis) planted on the roadside were also analyzed for Pb content. Current study revealed that Pb content in roadside soils and leaves of oil palm was 1.5 and 5.5 times higher than the safe level of Pb in soil and plant. It confirms that both soil and plant at the study site were contaminated by Pb. Current study also showed that SOM amendment significantly (P&lt;0.01) affected soluble Pb content in the soils. Adding OM to the soil at 30 Mg ha-1 to correct the level of SOC from very low to low was sufficient to significantly reduce soluble Pb in the soils. However, the application of 60 Mg ha-1 of OM triggered the increases in soluble Pb in the soils. Further increases in OM application to 90 Mg ha-1 resulted in significant increases in soluble Pb as compared with that in the soil receiving 30 Mg ha-1 of OM. In spite of the increases, the level of soluble Pb in the soils receiving 60 and 90 Mg ha-1 of OM was still much below the safe level of Pb in soil.

Taxonomy characterization and plumbum bioremediation of novel fungi

The objective of this study was to investigate the screening, taxonomy characterization, Pb biosorption, and application of the high Pb-resistant fungus F1 separated from the heavy metal contaminated soil. Fungus F1 was screened through metal concentration gradient ranging from 25 to 4000 mg L-1 . The internal transcribed spacers (ITS) of the strain was analyzed by molecular biotechnology. The adsorption conditions were also evaluated. The precipitation of fungus F1 was analyzed by Scanning Electron Microscopy (SEM), Fourier transformer infrared spectroscopy (FTIR) and energy dispersive X-ray (EDX) techniques. The Pb speciation was determined by BCR three-step sequential extraction. The highest concentration of fungus F1 resistance to Pb2+ was 3500 mg L-1 . The fungus was identified as Trichoderma asperellum. The optimum condition for the Pb2+ removal rate was discovered as follows: MTL: 3500 mg L-1 ; pH: 7; Pb2+ concentration: 800 mg L-1 ; temperature was 30 °C; initial biosorbent dosage: 6% (v/v). The surface chemical functional groups of fungus F1 were amino, hydroxyl, and carbonyl groups, which may be involved in the biosorption of Pb. Application test showed that the exchangeable, acid-and water soluble Pb were reduced, and the sulfide, organic combination state, and residual Pb were increased. With the preferable absorption capacity, fungus F1 was considered to have good prospects of bioremediation.

Improved geochemical modeling of lead solubility in contaminated soils by considering colloidal fractions and solid phase EXAFS speciation

Lead (Pb) is a common contaminant in soils at e.g. mining, shooting range, and glassworks sites. In order to make reliable risk assessments and appropriate decisions on various “gentle remediation options”, such as applying phosphate, compost, or zero-valent iron to soils, the binding mechanism of Pb and its speciation needs to be known. Multi-surface geochemical equilibrium models are useful tools for estimating trace metal solubility and speciation, but for Pb the predictions are often poor. This study evaluates the recent parameterization for Pb in the Visual MINTEQ code for its ability to predict the solubility of Pb at different pH values in four historically contaminated Swedish soils. As an independent validation of the model performance, the modeled solid-phase speciation was compared to measured Pb speciation retrieved using extended X-ray absorption fine structure (EXAFS) spectroscopy. Furthermore, potential artefacts by the presence of Pb colloids were investigated by filtering solutions through both 0.45 μm and 10 kDa filters. The model accuracy for predicting Pb solubility was improved compared with previous studies producing log root mean square error (RMSE) values below 0.42 in three out of four soils, just by using generic assumptions. The use of ultrafiltered (<10 kDa) instead of the 0.45 μm-filtered Pb concentrations lowered the RMSE with ∼0.4 log units in two soils, giving a more accurate evaluation of the model performance. EXAFS proved to be a useful tool for validating and constraining the model, since the solid phase speciation did not exactly agree with the modeled results using default assumptions. However, a sample-specific optimization of the amount of “active” solid organic matter and Al + Fe hydroxides resulted in improved prediction of Pb solubility as well as better agreement with the EXAFS measurements. Solubility of Pb in the fourth, As-rich soil was probably controlled by Pb5(AsO4)3Cl (mimetite) with a solubility product constant of 10−83.53.

Efficiency of Opuntia ficus in the phytoremediation of a soil contaminated with used motor oil and lead, compared to that of Lolium perenne and Aloe barbadensis

ABSTRACTIndustrial pollutants such as heavy metals and hydrocarbons in soils represent a serious concern due to their persistence and negative effects on the environment, affecting cellular processes in living organisms and even causing mutations and cancer. The main objectives of this work were to evaluate the efficiency of Opuntia ficus in the phytoremediation of a soil polluted with used motor oil. Two other species, one with different and one with similar characteristics, relatively, were used for comparison purposes: Lolium perenne and Aloe barbadensis. The effect of the plants on lead solubility and bioaccumulation, the biomass production of each specie and the microbial counts and bacterial identification for each experiment was studied. Total petroleum hydrocarbons (TPH) were measured every 5 weeks throughout the 20-week phytoremediation experiment. At the end of the experiment soluble Pb, Pb extracted by the plant species, microbiological counts, total biomass and bacterial species in soil were analyzed. Even though Lolium perenne showed the highest TPH removal (47%), Opuntia ficus produced the highest biomass and similar removal (46%). Since Opuntia ficus requires low amounts of water and grows fast, it would be a suitable option in the remediation of soils polluted with hydrocarbons and/or heavy metals.

Lead (Pb) Bioaccessibility and Mobility Assessment of Urban Soils and Composts: Fingerprinting Sources and Refining Risks to Support Urban Agriculture.

While the presence of legacy lead (Pb) in urban soil is well documented, less is known about the bioaccessibility, transport, and exposure pathways of urban soil Pb. We study Pb bioaccessibility in Roxbury and Dorchester, MA, urban gardens to assess exposure risk and identify remediation strategies, applicable locally and in urban gardens across the country. We work in partnership with The Food Project, which brings the goals and perspectives of local farmers to the center of the research process and enables efficient local application of results to reduce Pb exposure. We measure changes in Pb bioaccessibility as a function of growing material, grain size, and Pb source. In comparison to soils, compost has lower total Pb concentrations, has lower Pb solubility in gastric fluid, and limits fine particle resuspension. The mean bioaccessible Pb concentration of compost is 265 mg/kg, nearly an order of magnitude lower than that of soils, and compost contains 14% higher carbon content than soils, which may account for the observed 19% lower Pb bioaccessibility in compost. For all matrices (soil, raised bed fill, and compost) grain sizes <37 μm contain a disproportionate fraction of the total pool of bioaccessible Pb. Furthermore, the isotopic composition of Pb in the size fractions linked with resuspension and elevated blood lead levels is indicative of leaded gasoline and leaded paint even decades removed from the primary deposition of these sources.

Influence of lead on stabilization/solidification by ordinary Portland cement and magnesium phosphate cement

Inorganic binder-based stabilization/solidification (S/S) of Pb-contaminated soil is a commonly used remediation approach. This paper investigates the influences of soluble Pb species on the hydration process of two types of inorganic binders: ordinary Portland cement (OPC) and magnesium potassium phosphate cement (MKPC). The environmental leachability, compressive strength, and setting time of the cement products are assessed as the primary performance indicators. The mechanisms of Pb involved in the hydration process are analyzed through X-ray diffraction (XRD), hydration heat evolution, and thermogravimetric analyses. Results show that the presence of Pb imposes adverse impact on the compressive strength (decreased by 30.4%) and the final setting time (prolonged by 334.7%) of OPC, but it exerts much less influence on those of MKPC. The reduced strength and delayed setting are attributed to the retarded hydration reaction rate of OPC during the induction period. These results suggest that the OPC-based S/S of soluble Pb mainly depends on physical encapsulation by calcium-silicate-hydrate (CSH) gels. In contrast, in case of MKPC-based S/S process, chemical stabilization with residual phosphate (pyromorphite and lead phosphate precipitation) and physical fixation of cementitious struvite-K are the major mechanisms. Therefore, MKPC is a more efficient and chemically stable inorganic binder for the Pb S/S process.

Evaluating solubility of Zn, Pb, Cu and Cd in pyrite cinder using leaching tests and geochemical modelling

Production of sulfuric acid by roasting of pyrite (Fe sulfide) produces a Fe rich waste product, pyrite cinder (or pyrite ash), which often contains high levels of trace metals such as Zn and Pb. The chemical forms of the metals and their solubility in these materials are poorly known. To evaluate the risks associated with pyrite cinder and manage cinder contaminated sites efficiently more knowledge on the chemical processes in pyrite cinder is needed. In this study the solubility of Zn, Pb, Cu and Cd in a pyrite cinder from Bergvik, Sweden, was investigated. The objectives were to (i) identify the solubility controlling processes for Zn, Pb, Cu, and Cd in the pH range 3–9, (ii) characterize the Fe (hydr)oxides present in these materials and (iii) to identify implications for management strategies of pyrite cinder contaminated sites. This was done using a combination of batch experiments, selective extractions, X-ray absorption spectroscopy and geochemical modelling. Hematite was identified as the dominating Fe mineral in the cinder. A geochemical model using generic binding parameters could describe the solubility of Zn, Cu and Cd in the cinder well, while Pb concentrations were generally underestimated. The modelling indicated that adsorption to Fe (hydr)oxides was the most important solubility controlling mechanism for all metals, except for Zn at pH > 6, where Zn minerals seemed to control the concentrations of Zn. To minimize leaching of Zn, Pb, Cu and Cd from cinder materials, remediation strategies should be focused on keeping the pH > 6.

Adsorption of soluble Pb(II) by a photocrosslinked polysaccharide hybrid: A swelling-adsorption correlation study

A biosorbent for adsorption of soluble, inorganic Pb(II) was prepared through a photocrosslinking of a mixture of xanthan gum and guar gum at various mass ratios. The polysaccharide mixes were irradiated using UV A in presence of benzophenone. Chemical crosslinks were formed which led to a controlled swelling of the polysaccharide mix (swelling ratio <20%), referred as crosslinked hybrid in the text. The hybrids were characterized for microstructure, rheology, surface area and surface charge behavior. Interesting changes in crystallographic pattern, both in the pre and the post adsorption stages, was investigated using x-ray diffraction technique. Adsorption efficiency was estimated in respect of blend composition, adsorbate-adsorbent concentration and pH under competitive and non-competitive conditions. A correlation between the swelling of the crosslinked hybrid and the metal adsorption was drawn at various pH to elucidate an interaction between the two phenomena.

Effect of controlled-release urea on heavy metal mobility in a multimetal-contaminated soil

Controlled-release N fertilizers can affect the availability of heavy metals in the contaminated paddy soil. A soil incubation experiment was conducted to investigate the effects of prilled urea (PU), S-coated urea (SCU), and polymer-coated urea (PCU) on the solubility and availability of heavy metals Cd, Pb, Cu, and Zn in a multimetal-contaminated soil. The results showed that the application of different coated urea significantly affected the solubility and availability of heavy metals. At 5 d of incubation, the application of PU, SCU, and PCU had significantly decreased the concentrations of water-soluble and available Cd, Pb, Cu, and Zn, when compared with the control. At 60 d of incubation, the depletory effects of PU on water-soluble and available heavy metals had reduced, and the initial decrease in the concentrations of water-soluble Cd, Pb, Cu, and Zn caused by SCU had changed to an increase. The concentrations of water-soluble Pb, Cu, and Zn in the SCU-treated soil were higher than those in the control. Application with PCU led to a higher water-soluble Cu than that in the control, while the available Cd, Pb, and Zn were lower than those in the control. The effect of different coated urea was much stronger on the water solubility of the heavy metals than on their availability. The effects of controlled-release urea on the transformation of heavy metals resulted in changes in the concentrations of NH+4, water-soluble SO2−4, and soil pH. The results further suggested that PCU could be used in dry farming operations in multimetal-contaminated acid soils.