Metal Fixation Research Articles

Cd Distribution in the Tissues of Oysters (Crassostrea Gigas) Exposed Chronically In Situ

This study was designed to monitor the evolution of the nature of Cd-binding molecular compounds in oysters transplanted from a low-contaminated area to a highly Cd-polluted site. These compounds have been compared to those found in oysters from the low-contaminated site, used as control, and from the native molluscs of the polluted area. We have also studied the influence of the length of exposure, collecting oysters after transplantation having been going on for 1 or 3 months. We have compared the quantities of Cd bound to soluble or insoluble compounds. The Cd distribution among cytosolic compounds was analyzed by gel permeation. Four classes of Cd-binding molecular compounds were separated and their relative significance in metal fixation was found to differ among resident and transplanted oysters.

Interactive Sorption of Metal Ions and Humic Acids onto Mineral Particles

The sorption of metal ions (Pb2+, Zn2+ and Cu2+) and soil humic acids (HA) from aqueous solutions onto mineral particles (sand, calcite and clay) was investigated using a batch equilibrium system. The sorption reactions in two- component systems (heavy metals-mineral particles and humic acids- mineral particles), as well as interactions in three-component system (heavy metals-humic acids-mineral particles) were examined. Results showed that the presence of humic acids, dissolved or bound onto mineral surfaces, considerably influenced the fixation of heavy metals. The various effects, depending on mineral type, humic concentration and specific metal-ion, were observed in three- component system. Sorption of Cu2+-ions on all minerals studied rapidly increased as the concentration of dissolved HA increased. The amount of Pb2+-ions sorbed on sand slightly decreased, while on kaolin increased between 15 and 20%. Sorption of Zn2+-ions on all minerals studied decreased at pH 4. At pH 5.5 the sorption of Zn2+-ions onto calcite decreased, while on kaolin and sand increased as a function of the humic acid concentration giving the curve with maximum at c(HA) = 2.5 mmol C L-1. At pH 6.5 sorption onto kaolin and sand increased. This effect occurs as a result of the conditional stability constant of Zn-HA complexes increasing at higher pH which in turn promotes the chelation of Zn2+-ions to mineral- bound humic substances. The enhanced sorption of metal ions from the aqueous phase in three-component systems is not only the result of mineral sorption of free metals but also the result of chelation with HA sorbed on the mineral surface.

Using bare image plates for imaging patients with metallic external fixation devices.

Using bare image plates for imaging patients with metallic external fixation devices.

Rivet-like titanium clamps for refixation of bone covers after craniotomy--radiologic identification, safety and image quality in CT and MR studies

The MRI and CT compatibility of a new design of metallic fixation implants for cranial bone flaps was investigated experimentally and following clinical application in craniotomy patients. Is imaging quality impaired through implant-induced artifacts? Possible induced movement and heating of the clamp implant as well as the magnitude of susceptibility artifacts were assessed experimentally by MRI at 1.5 T. Additionally, implant-induced artifacts were evaluated under clinical conditions for all relevant MRI-sequences in 100 craniotomy patients whose skull flaps were re-affixed using the new clamp implant. In T1-weighted spin echo and fast spin echo sequences the sizes of implant-induced artifacts were equal to the size of the implant or slightly larger; in T2-weighted gradient echo images artifacts were maximally double the size of the implant itself. Induced movement or heating was not observed. The safety in radiological imaging of titanium clamp implants for fixation of craniotomy bone flaps was established experimentally as well as under clinical conditions. The clamps can be easily identified by radiological imaging, cause no hazards to the patients, and have little effect on image quality.

Characterisation and prediction of sediment-hosted ore deposits using sequence stratigraphy

The processes that form stratabound ore deposits involve diagenesis, fluid-flow, rock–fluid interaction and metal fixation which, like the maturation, migration and entrapment of hydrocarbons are integral aspects of basin history. Sequence stratigraphy is a method by which the stratigraphic record of sedimentary basins may be analyzed and placed in facies-dependant depositional units related to changes in relative sea level. Here we show how some of the concepts of sequence stratigraphy can be applied in the interpretation and better understanding of known metal generative zones and in the prediction of potential host rocks of sedimentary ore deposits. Sequence stratigraphic concepts are of most use in explaining and predicting the juxtaposition of metal- or sulphur-generative sediments such as evaporites, red-beds and organic-rich shales, and in understanding mineralization associated with black shales, hardgrounds and reworking surfaces (placer deposits). The analysis of depositional sequences may also enable predictions to be made concerning likely ore-hosts, such as MVT mineralization in carbonate reefs and reservoir sands. The final position of a sedimentary ore deposit is dependent on (1) the geometry of the sedimentary sequence, (2) the depositional environments (i.e. specific lithologies) within each systems tract, and (3) the structure of the basin. We test this model by creating a sequence stratigraphic model for the Precambrian Aberfeldy barite deposit of Scotland and then consider other horizons in the Dalradian succession that may also stratiform mineral deposits.

Cranial bone flap fixation clamps: compatibility at MR imaging.

Metallic cranial bone flap fixation clamps were tested for compatibility at 1.5-T magnetic resonance (MR) imaging with standardized techniques. There was no magnetic field attraction, heating was minor, and artifacts involved a relatively small signal void. These data indicate that bone flap fixation clamps will not present risks to patients undergoing MR imaging procedures with MR systems of 1.5 T or less.

Intramedullary fixation of distal femoral diaphyseal osteotomies with absorbable self-reinforced poly-L-lactide and metallic intramedullary rods assessed by plain radiographs, quantitative computed tomography, and magnetic resonance imaging: an experimental study in rabbits.

Osteotomies of distal femoral diaphysis were fixed intramedullary with self-reinforced poly-L-lactide acid (SR-PLLA) rods in 19 and with metallic rods in 34 adult rabbits. The follow-up times were 8, 16, 24, and 48 weeks. Plain radiographs, computed tomography (CT), quantitative computed tomography (QCT), and magnetic resonance imaging (MRI) were used to evaluate the bone changes at two different levels of the osteotomy region. There were no significant differences in cortical bone density compared to the intact in the SR-PLLA fixed femurs at the osteotomy site. In the metallic-fixed femurs, the density values were significantly lower as compared to the contralateral femurs. There was a significant reduction of the cortical bone density values in SR-PLLA fixed femurs compared to the intact control side outside the osteotomy area at 8 (p = 0.01), at 16 (p = 0.0001), and at 24 weeks (p = 0.0003). In the metallic-fixed femurs significant reductions at 8 weeks (p = 0.02), at 16 weeks (p = 0.01), at 24 weeks (p = 0.009), and at 48 weeks (p = 0.002) were found compared with the intact control. MRI depicted well the SR-PLLA cases allowing studies without removal of the implant. On the contrary, abundant disturbing metallic artifacts were detected during investigation of the metallic-fixed femurs. In conclusion, our results indicated that CT is useful to evaluate the quality of reduction and internal fixation. Furthermore, the constant presence of internal metallic fixation seems to eventually cause osteoporosis in the cortical region of the femur. However, this stress protection effect of intramedullary fixation on the femoral diaphysis seems to be avoided by using an absorbable SR-PLLA rod, thus resulting in a better quality of bone when the osteotomies are healed.

Wastewater sludge conditioning by fly ash

Conditioning wastewater sludge from the City of Regina Wastewater Treatment Plant by fly ash from Boundary Dam Power Station, Saskatchewan, Canada, was studied. Toxicity characteristic leaching procedure (TCLP), equilibrium leach test (ELT), and long-term leaching test (LTLT) were used to investigate the leachability of heavy metals. Results from these leaching tests indicated that, on the basis of concentrations of microorganisms and heavy metals (Cd, Cr, Cu, Ni and Zn), the sludge produced at the Regina Wastewater Treatment Plant conditioned by the locally available fly ash can be disposed of in landfills and used as a soil conditioner for land application. Sorption, and silicate and hydroxide precipitations were considered to be the three important mechanisms in fixation of heavy metals. High pH conditions were considered to be the predominant mechanism in killing microorganisms.

Utilization of sewage sludge ashes in the brick and tile industry

Several aspects of using ashes from sewage sludge incineration in the brick and tile industry have been examined. After discussing the item of ash production in Germany, the impact of different wastewater treatment methods is described; for instance, the use of precipitation agents containing iron will considerably influence the ash quality. Depending on their respective chemical composition, different ashes have different effects on the ceramic qualities of the bricks made of clay blended with ashes. These effects will be shown in regard to the major ceramic parameters. Similarly, the quality of the ashes also influences the elution behaviour and the mineral fixation of heavy metals.

Effect of carbonation on properties of blended and non-blended cement solidified waste forms

Five types of cement and two pozzolans were used to investigate the influence of carbonation on the properties of solidified waste forms. The waste chosen was a commercially blended product which was mixed with cement and then cured in three different environments: nitrogen, air and carbon dioxide for 28 days. Samples were examined for strength development, setting time, microstructural development and leachate metal fixation. Samples cured in a carbon dioxide rich environment showed distinct changes in mechanical properties, microstructure and fixation of metal species. Carbonation was also found to play an important role in the hydration of the binder waste form mix. Carbonated solidified products were characterised by enhanced calcite contents, higher strength values and a significant reduction in leachable metals concentration for all the cement types examined when compared with samples cured in nitrogen. It is also shown that the type of cement or cement-blended system can be optimised to obtain maximum improvement in fixation of waste species in a carbonated product.

Comparison of costs in ankle fractures treated with absorbable or metallic fixation devices

Comparison of costs in ankle fractures treated with absorbable or metallic fixation devices

Utilization of sewage sludge ashes in the brick and tile industry

Several aspects of using ashes from sewage sludge incineration in the brick and tile industry have been examined. After discussing the item of ash production in Germany, the impact of different wastewater treatment methods is described. for instance, the use of precipitation agents containing iron %vill considerably influence the ash quality. Depending on their respective chemical composition, different ashes have different effects on the ceramic qualities of the bricks made of clay blended with ashes. These effects will be shown in regard to the major ceramic parameters. Similarly, the quality of the ashes also influences the elution behaviour and the mineral fixation of heavy metals.

Fixation of lead in contaminated soils by co‐agglomeration with metal binding agents*

Abstract Adsorption of lead from an aqueous solution by both agricultural peat moss and soil has been measured. The results may be described by a Langmuir isotherm model. Adsorption isotherms fitted the “H”; type described in the Giles classification. Saturation adsorption was reached at equilibrium lead concentrations > 3000 mg/L for peat, compared with ∼ 250 mg/L for soil. Calculation of the isotherm parameters showed the maximum lead adsorption to be 150 mg lead/g of peat. This compared with only 12.64 mg/g of lead for soil alone. Several tests were carried out to evaluate the lead binding capacity of peat in a spiked soil sample. Results from leaching tests (Environmental Protection Agency, EPA, Toxicity Characteristic Leaching Procedure, TCLP, at pH 2.9) on soil‐peat mixtures confirmed the excellent metal binding capacity of peat in the samples tested. The amount of lead leached from a soil sample, spiked with 1840 mg/kg of water‐soluble lead, decreased with increasing amounts of peat loading. Total fixation was achieved at a peat loading of 20%. In addition to peat, several other agents were tested for their suitability as fixing agents in heavy‐metal contaminated soils. These included: gypsum, lime, autoshredder residue, fly ash, and a sample of oil sands fines. Liquid phase agglomeration was used to coagglomerate these materials with soil as a means to fix lead in artificially contaminated samples. The agglomeration process is advantageous in that it allows concurrent fixation of heavy metals and solvent extraction of organic contaminants. In terms of material handling and equipment, a combined process will be more economical than conventional methods requiring separate extraction and leaching steps.

The role of humic substances in the transport and fixation of metals of economic interest (Au, Pt, Pd, U, V)

The role of humic substances in the transport and fixation of metals of economic interest (Au, Pt, Pd, U, V)

Revision of failed prosthetic anterior cruciate ligament reconstruction.

Revision of failed prosthetic anterior cruciate ligament reconstructions will continue to be necessary as previously placed prosthetic devices fail with time. These patients often present with recurrent instability, pain, swelling, or effusions. Graft rupture and the generation of particulate debris are common causes of these symptoms. To effectively treat these patients requires careful preoperative evaluation and planning. Operative treatment includes removing the prosthesis and metal fixation devices, evaluating femoral and tibial bone stock, and determining adequacy of previous tunnel position. Staging of the operation may be a necessity if significant bone loss or poor tunnel position on either the femoral or tibial side requires bone grafting. The use of an autogenous bone-patellar tendon-bone graft is suggested and has proven to be effective in restoring knee stability in these revision cases. The ultimate outcome following revision of failed prosthetic ligaments may be limited by associated intraarticular pathology often seen in this patient population.

Finite element stress analysis of a hybrid fracture fixation plate

Metal plates are commonly used in the operative treatment of bone fractures. Rigid metal plates stabilize the fracture site, maintain good contact between bone fragments and allow early weight bearing and patient mobility. However, treatment with rigid metal plates can cause localized bone atrophy due to stress-shielding and interference with blood circulation, and the weakened bone can refracture after plate removal. A hybrid bone plate system that combines the torsional and bending rigidity of a metal plate with the axial compliance of a polymer insert has been designed. A three-dimensional, quarter-symmetric finite element model was generated for a canine femur diaphysis plated with this metal/polymer hybrid design. A model with a standard metal fixation plate was also generated for comparison purposes. The stress state in the underlying bone was examined for several loading conditions taken from published in vivo studies. The finite element model was used to study the performance of biodegradable polymer inserts in the plate system. The flexible plate reduced stress-shielding effects at the fracture site when subjected to an axial load. The bending strength of the plate was not compromised by the addition of the polymer inserts. Biodegradable inserts further enhanced the performance of the new plate design, transferring less of the axial load to the plate as the inserts broke down.

A combined frontoorbital and occipital advancement technique for use in total calvarial reconstruction

The management of infants with bilateral coronal synostosis and resultant brachyturricephaly poses a significant therapeutic challenge. The application of total calvarial reconstruction to the treatment of this problem has represented a major recent innovation that has substantially improved the cosmetic results in this patient population. However, rigid fixation of the reconstructed calvaria is often required to maintain the correction achieved and to provide protection for the underlying brain. The requirement of extensive fixation constitutes a significant disadvantage for the use of this procedure in infants and young children. In this report, the authors describe an approach to the treatment of this problem that incorporates a series of tongue-in-groove osteotomies to provide increased stability to advancements of both the frontal and occipital regions in conjunction with cranial height reduction, while minimizing the need for metallic fixation. With this approach, the reconstructed skull is sturdy enough to resist the compressive force applied by the weight of the child's head immediately after surgery, but retains the ability to expand progressively. The authors have found the cosmetic results to be extremely gratifying. In this article they present their experience with this technique in seven children.

The Role of Proteins in the Fixation of Heavy Metals on Oak Leaves

Abstract Dry oak leaves exhibit the property of accumulating metals when exposed to atmospheric pollution and thus can be used as bioindicators of metal pollution. In this paper the role of proteins, one of the components of leaves involved in the metal fixation, has been investigated. Proteins and protein-metal complexes were extracted purified, separated and concentrated by means of ion exchange chromatography and electophoresis. The results revealed that three different types of proteins having different molecular weights are responsible for metal fixation. Dedicated to Professor D. Klockow on the occasion of his 60th birthday.

Metal fixation and mobilisation in the sediments of the Afon Goch estuary — Dulas Bay, Anglesey

The surface drainage waters of Parys Mountain, Anglesey (Wales), a site of former mining for base metals, are highly acidic and metal-rich due to the oxidation of sulphide minerals. These acid waters mix with more neutral waters in the Afon Goch, downstream of Parys Mountain, allowing the formation of ochre precipitates which are found throughout the length of the Afon Goch and Dulas Bay. X-ray fluorescence (XRF) analysis of the ochres that settle where the Afon Goch enters Dulas Bay (Fe 2O 3 - 18 wt%), reveals that they are heavily contaminated with Cu (13,000 μg/g) and Zn (7700 μg/g). These sediments are black immediately below the surface and porewater analysis confirms that sulphate reduction is taking place. Samples of both stream ochre and anoxic black mud have been analysed by EXAFS spectroscopy. Data from the EXAFS analysis of the ochre sample reveals that the Fe, Cu and Zn are bonded to oxygen in poorly ordered or amorphous solids. In the anoxic black mud, however, Fe, Cu and Zn are all present as sulphides. The Fe sulphide is either amorphous or poorly ordered whereas Zn forms a discrete sulphide phase similar to sphalerite. The Cu sulphide has short range order with a chalcopyrite-like structure. Sequential Extraction analysis of the same samples was also performed. For the ochre sample, Cu and Zn release is controlled by the Fe hydrated oxides, being recovered primarily in the mildly acid ‘Carbonate’ and more strongly acid and reducing ‘Reducible’ fractions. Fe and Zn are also recovered in these fractions from the black mud, indicating that these metals are present as acid-soluble sulphides. Cu, however, is almost exclusively recovered in the ‘Oxidisable’ fraction, indicating that it is incorporated into a more stable sulphide such as chalcopyrite.

Overview and Classification of Spinal Infections

Hematogenous spread is the most common cause for vertebral osteomyelitis. S. aureus is the most common organism in pyogenic vertebral osteomyelitis. Hematogenous osteomyelitis is common among diabetics and intravenous drug abusers. Tuberculous spondylitis remains common worldwide. In general, vertebral body infections not responding to antibiotic treatment and those creating unacceptable deformity or neurologic compromise require debridement via an anterior approach with strut grafting. Posterior infections are almost always postsurgical and require posterior irrigation and debridement in addition to antibiotics. Abscesses within the canal require antibiotics and surgical debridement especially when neurologic symptoms are present. Infections within the canal are approached posteriorly unless the pathology involves the anterior spine. Use of metal fixation within the site of an adequately debrided spinal infection is controversial but necessary on rare occasions. Posterior fixation for anterior infections is preferred. Much has been written about spinal infections and their treatment. Landmark articles and additional comprehensive sources on spinal infections have been included in the references.