A hydroxyapatite phantom material for the calibration of in vivo x-ray fluorescence systems of bone strontium and lead quantification

A hydroxyaptite [HAp; Ca5(PO4)3OH] phantom material was developed with the goal of improving the calibration protocol of the 125I-induced in vivo X-ray fluorescence (IVXRF) system of bone strontium quantification with further application to other IVXRF bone metal quantification systems, particulary those associated with bone lead quantification. It was found that calcium can be prepared pure of inherent contamination from strontium (and other elements) through a hydroxide precipitation producing pure Ca(OH)2, thereby, allowing for the production of a blank phantom which has not been available previously. The pure Ca(OH)2 can then be used for the preparation of pure CaHPO4 ⋅ 2H2O. A solid state pure HAp phantom can then be prepared by reaction of Ca(OH)2 and CaHPO4 ⋅ 2H2O mixed as to produce a Ca/P mole ratio of 1.67, that in HAp and the mineral phase of bone, in the presence of a setting solution prepared as to raise the total phosphate concentration of the solution by increasing the solubility CaHPO4 ⋅ 2H2O and thereby precipitating HAp. The procedure can only be used to prepare phantoms in which doping with the analyte does not disturb the Ca/P ratio substantially. In cases in which phantoms are to be prepared with high concentrations of strontium, the cement mixture can be modified as to introduce strontium in the form of Sr(OH)2 ⋅ 8H2O as to maintain a (Ca + Sr)/P ratio of 1.67. It was found by both X-ray diffraction spectrometry and Raman spectroscopy studies that strontium substitutes for calcium as in bone when preparing phantoms by this route. The necessity for the blank bone phantoms was assessed through the first blank bone phantom measurement and Monte Carlo simulations. It was found that for the 125I-induced IVXRF system of bone strontium quantification, the source, 125I brachytherapy seeds may be contributing coherently and incoherently scattered zirconium X-rays to the measured spectra, thereby requiring the use of the blank bone phantom as a means of improving the overall quantification methodology. Monte Carlo simulations were employed to evaluate any improvement by the introduction of HAp phantoms into the coherent normalization-based calibration procedure. It was found that HAp phantoms remove the need for a coherent conversion factor (CCF) thereby potentially increasing accuracy of the quantification. Further, it was found that in order for soft tissue attenuation corrections to be possible using spectroscopic information alone, HAp along with a suitable soft tissue surrogate material need to be employed. The HAp phantom material was used for the evaluations of portable X-ray analyzer systems for their potential for IVXRF quantification of lead and strontium with a focus on a comparison between tungsten, silver and rhodium target systems. Silver and rhodium target X-ray tube systems were found to be comparable for this quantification.

A hydroxyapatite phantom material for the calibration of in vivo x-ray fluorescence systems of bone strontium and lead quantification

A hydroxyaptite [HAp; Ca5(PO4)3OH] phantom material was developed with the goal of improving the calibration protocol of the 125I-induced in vivo X-ray fluorescence (IVXRF) system of bone strontium quantification with further application to other IVXRF bone metal quantification systems, particulary those associated with bone lead quantification. It was found that calcium can be prepared pure of inherent contamination from strontium (and other elements) through a hydroxide precipitation producing pure Ca(OH)2, thereby, allowing for the production of a blank phantom which has not been available previously. The pure Ca(OH)2 can then be used for the preparation of pure CaHPO4 ⋅ 2H2O. A solid state pure HAp phantom can then be prepared by reaction of Ca(OH)2 and CaHPO4 ⋅ 2H2O mixed as to produce a Ca/P mole ratio of 1.67, that in HAp and the mineral phase of bone, in the presence of a setting solution prepared as to raise the total phosphate concentration of the solution by increasing the solubility CaHPO4 ⋅ 2H2O and thereby precipitating HAp. The procedure can only be used to prepare phantoms in which doping with the analyte does not disturb the Ca/P ratio substantially. In cases in which phantoms are to be prepared with high concentrations of strontium, the cement mixture can be modified as to introduce strontium in the form of Sr(OH)2 ⋅ 8H2O as to maintain a (Ca + Sr)/P ratio of 1.67. It was found by both X-ray diffraction spectrometry and Raman spectroscopy studies that strontium substitutes for calcium as in bone when preparing phantoms by this route. The necessity for the blank bone phantoms was assessed through the first blank bone phantom measurement and Monte Carlo simulations. It was found that for the 125I-induced IVXRF system of bone strontium quantification, the source, 125I brachytherapy seeds may be contributing coherently and incoherently scattered zirconium X-rays to the measured spectra, thereby requiring the use of the blank bone phantom as a means of improving the overall quantification methodology. Monte Carlo simulations were employed to evaluate any improvement by the introduction of HAp phantoms into the coherent normalization-based calibration procedure. It was found that HAp phantoms remove the need for a coherent conversion factor (CCF) thereby potentially increasing accuracy of the quantification. Further, it was found that in order for soft tissue attenuation corrections to be possible using spectroscopic information alone, HAp along with a suitable soft tissue surrogate material need to be employed. The HAp phantom material was used for the evaluations of portable X-ray analyzer systems for their potential for IVXRF quantification of lead and strontium with a focus on a comparison between tungsten, silver and rhodium target systems. Silver and rhodium target X-ray tube systems were found to be comparable for this quantification.

Association of periphytic diatom species of artificial substrate in lotic environments in the Arroio Sampaio Basin, RS, Brazil: relationships with abiotic variables

Associations of diatom species were identified, in the Arroio Sampaio Basin, Rio Grande do Sul, Brazil, based on monthly samplings over a year along Arroio Sampaio and its main tributaries, using polyamide thread as an artificial substrate. The species groupings showed four different environments: medium-lower course of Arroio Sampaio; and lower course of Arroio Teresinha; upper course of Arroio Sampaio; and lower course of Arroio Duvidosa. Among the physical and chemical variables measured, water pollution, particularly organic contamination and eutrophication, measured from BOD5 and total phosphate concentration, respectively, appeared to be one of the most important environmental factors determining the composition and structure of species associations in the area studied.

Phosphate and slow vacuolar channels in Beta vulgaris

Movement of phosphate through slow vacuolar (SV) ion channels and the effects of phosphate on SV currents were investigated using vacuoles from Beta vulgaris L. When the vacuoles contained 50 mM phosphate, the addition of phosphate to the bath shifted the apparent reversal potential for whole vacuole currents to more positive values, suggesting an outward rectifying current due to movement of phosphate ions out of the vacuole. However absolute values for reversal potentials obtained from the current-voltage curves and tail currents for whole vacuoles suggested that the membranes were relatively impermeable to phosphate. Single-channel data showed that the vacuole preparations contained more than one species of ion channel and therefore the whole-vacuole data will not give definitive information about individual species of ion channels. One of the channels had a single channel reversal potential that indicated a permeability of H2PO4- ions relative to Cl- of 7. The probability of this outwardly rectifying channel being open had a marked dependence on voltage and, in these experiments, it was effectively closed for potentials negative of +20 mV. The single-channel conductance was 19.4 ± 3.1 pS with 50 mM KH2PO4 in the vacuole and 10 mM total phosphate concentration in the bath. A channel with these characteristics has not been reported previously. In addition to the data identifying a phosphate channel, it was found that the presence of phosphate in the bath solution slowed the rate of activation of the SV currents. This effect was partially reversed when phosphate was removed from the bath.

High Gradient Magnetic Separation Technique for Wastewater Treatment

Smit Nymegen Magnetic Water treatment Systems (MWS), a business group of Smit Transformatoren BV, has recently developed a very efficient magnet for wastewater treatment. The magnet is the core element of a complete system to eliminate phosphates, heavy metals and other pollutants from wastewater. The system is based on the attachment of wastewater pollutants to a magnetic carrier material (magnetite) and a subsequent magnetic separation of the magnetite-pollutant conglomerates. After separation, the magnetite is recovered and re-used in the process. Main advantages of the magnetic separation process are:▸high elimination performance▸low power input for magnet operation▸compact process▸low space requirements▸no clogging because of open matrix structure. The development of the magnetic system has been focused on the phosphate-removal from effluents of sewage treatment plants. Being a tertiary treatment, magnetic phosphate removal can be applied after any type of sewage treatment and it does not interfere with the biological process. Pilot plant tests at various sewage works showed that magnetic separation reduces the total-phosphate concentration to values as low as 0.1-0.5 mg/l. The system will be demonstrated in two full-scale plants with a capacity of 300 m3/h and 600 m3/h, respectively. The costs of magnetic phosphate removal (Dfl. 12,- to 18,-) are competitive with those of other phosphate removal techniques. The development of the magnetic phosphate removal system is granted by the Dutch Ministries of Housing, Physical Planning and Environment, Economic Affairs and Transport and Public Works.

pH gradient as an additional driving force in the renal re-absorption of phosphate

The effects of the Na+ gradient and pH on phosphate uptake were studied in brush-border membrane vesicles isolated from rat kidney cortex. The initial rates of Na(+)-dependent phosphate uptake were measured at pH 6.5, 7.5 and 8.5 in the presence of sodium gluconate. At a constant total phosphate concentration, the transport values at pH 7.5 and 8.5 were similar, but at pH 6.5 the influx was 31% of that at pH 7.5. However, when the concentration of bivalent phosphate was kept constant at all three pH values, the effect of pH was less pronounced; at pH 6.5, phosphate influx was 73% of that measured at pH 7.5. The Na(+)-dependent phosphate uptake was also influenced by a transmembrane pH difference; an outwardly directed H+ gradient stimulated the uptake by 48%, whereas an inwardly directed H+ gradient inhibited the uptake by 15%. Phosphate on the trans (intravesicular) side stimulated the Na(+)-gradient-dependent phosphate transport by 59%, 93% and 49%, and the Na(+)-gradient-independent phosphate transport by 240%, 280% and 244%, at pH 6.5, 7.5 and 8.5 respectively. However, in both cases, at pH 6.5 the maximal stimulation was seen only when the concentration of bivalent trans phosphate was the same as at pH 7.5. In the absence of a Na+ gradient, but in the presence of Na+, an outwardly directed H+ gradient provided the driving force for the transient hyperaccumulation of phosphate. The rate of uptake was dependent on the magnitude of the H+ gradient. These results indicate that: (1) the bivalent form of phosphate is the form of phosphate recognized by the carrier on both sides of the membrane; (2) protons are both activators and allosteric modulators of the phosphate carrier; (3) the combined action of both the Na+ (out/in) and H+ (in/out) gradients on the phosphate carrier contribute to regulate efficiently the re-absorption of phosphate.

PHOSPHATE ION AS A PROMOTER CATALYST OF RESPIRATION

The active component of phosphate solutions, in relation to promoter action on oxidising enzymes, is the PO4''' ion. This is shown by the demonstration of a hyperbolic relationship between per cent production of CO2 (of Elodea) and pPO4, the measure of the phosphate ion potential. This is consistent with the rate of respiration as affected by changing pPO4 through change of total phosphate concentration while pH is kept constant. The equation for this relationship is (CO2 – a) (pPO4 – b)n = K where a, b, n, and K are constants and n = 1. The same relationship to phosphate ion concentration, expressed by the equation (Activity of enzyme) (pPO4)n = K, where n and K are constants and n varies from 1 to 6 under different conditions, appears to hold for some other enzyme actions, including those of peroxidase and pancreatic lipase.