Levels Of Bi Research Articles

Characterization of a long range transport pollution episode affecting PM in SW Spain

A multidisciplinary study on aerosol characterization was performed at the regional background monitoring station of El Arenosillo, in SW Spain, between 28 June and 5 July 2006. The main aim of the Arenosillo aerosol measurement campaign 2006 was to compare the results of aerosol characterization obtained by different groups by measuring physical and chemical parameters using optical methods and in situ sampling. The campaign coincided with a long-range transport episode from Western Iberia, passing through the Gulf of Cadiz and the Straits of Gibraltar towards the study area. The results of the variability of PM levels and chemical composition of PM10, PM2.5 and PM1 at El Arenosillo and at three nearby regional and urban background sites were interpreted. Mean levels measured during the campaign reached 23, 15 and 12 microg m(-3) for PM10, PM2.5 and PM1, respectively, at El Arenosillo. PM during the Arenosillo campaign 2006 was dominated by the secondary inorganic aerosols (SIA, 24, 38 and 39% of PM10, PM2.5 and PM1 mass), carbonaceous aerosols (17, 21 and 23% of the mass), crustal material (13, 9 and 4%), and sea spray (10, 5 and 1%). These values are within the usual range of regional background sites of Southern Spain with the exception of the relatively low crustal load and the high SIA levels. Two major PM episodes were differentiated. The first one was characterized by high levels of Bi, As, Pb, Se, P and Zn, which are the main tracers of the industrial emissions near the town of Huelva. High concentrations of these elements were also recorded at the nearby sites. In the second episode, maximum levels of SO4(2-), V and coarse Cu as well as the bulk mass of PM1 were determined, tracing the polluted air mass transport from Western Iberia through the Straits of Gibraltar. These results underline the importance of the influence of long-range transport of pollutants on the levels and composition of regional background PM in SW Iberia, where local emissions may also play a role.

Source origin of trace elements in PM from regional background, urban and industrial sites of Spain

Despite their significant role in source apportionment analysis, studies dedicated to the identification of tracer elements of emission sources of atmospheric particulate matter based on air quality data are relatively scarce. The studies describing tracer elements of specific sources currently available in the literature mostly focus on emissions from traffic or large-scale combustion processes (e.g. power plants), but not on specific industrial processes. Furthermore, marker elements are not usually determined at receptor sites, but during emission. In our study, trace element concentrations in PM 10 and PM 2.5 were determined at 33 monitoring stations in Spain throughout the period 1995–2006. Industrial emissions from different forms of metallurgy (steel, stainless steel, copper, zinc), ceramic and petrochemical industries were evaluated. Results obtained at sites with no significant industrial development allowed us to define usual concentration ranges for a number of trace elements in rural and urban background environments. At industrial and traffic hotspots, average trace metal concentrations were highest, exceeding rural background levels by even one order of magnitude in the cases of Cr, Mn, Cu, Zn, As, Sn, W, V, Ni, Cs and Pb. Steel production emissions were linked to high levels of Cr, Mn, Ni, Zn, Mo, Cd, Se and Sn (and probably Pb). Copper metallurgy areas showed high levels of As, Bi, Ga and Cu. Zinc metallurgy was characterised by high levels of Zn and Cd. Glazed ceramic production areas were linked to high levels of Zn, As, Se, Zr, Cs, Tl, Li, Co and Pb. High levels of Ni and V (in association) were tracers of petrochemical plants and/or fuel-oil combustion. At one site under the influence of heavy vessel traffic these elements could be considered tracers (although not exclusively) of shipping emissions. Levels of Zn–Ba and Cu–Sb were relatively high in urban areas when compared with industrialised regions due to tyre and brake abrasion, respectively.

Major and trace elements in paddy soil contaminated by Pb–Zn mining: a case study of Kočani Field, Macedonia

The objective of this study was to assess the bulk chemical composition as well as the extent and severity of heavy metal contamination in the paddy soil of Kocani Field (eastern Macedonia). The results revealed that the paddy soil of the western part of Kocani Field is severely contaminated with Pb, Zn, As and Cd in the vicinity of the Zletovska River due to irrigation with riverine water that is severely affected by acid mine and tailing effluents from the Pb-Zn mine in Zletovo. The detected total concentrations of these metals are far above the threshold values considered to be phytotoxically excessive for surface soil. The paddy soil in the vicinity of the Zletovska River was also found to exhibit elevated levels of Ba, Th, U, V, W, Mo, Cu, Sb, Bi, Ag, Au, Hg and Tl, with concentrations above their generally accepted median concentration values obtained during this study. A correlation matrix revealed that the Mn and Fe oxides/hydroxides are the most important carrier phase for several trace elements, with the exception of rare earth elements (REEs). These also represent a major sink for the observed heavy metal pollution of the soil. REEs are mostly associated with two phases: light (L)REEs are bound to K-Al, while heavy (H)REEs are bound to Mg-bearing minerals. Although there is no direct evidence of a health risk, the paddy soil in the vicinity of Zletovska River needs further investigation and an assessment should be made of its suitability for agricultural use, particularly in view of the highly elevated concentrations of Pb, Zn, As and Cd.

Bi modified Pd/SnO2 catalysts for water denitration

A Pd/SnO2 catalyst was doped with low concentrations of Bi in order to induce selective poisoning of sites on the Pd surface in order to test a hypothesis that specific surface sites are responsible for ammonium formation during the catalytic hydrogenation of nitrates from drinking water. Initial addition of low levels of Bi appeared to selectively titrate high-energy surface Pd atoms located in the high index planes of the Pd crystallites. Addition of Bi had little effect on catalyst activity but modified selectivity profiles of nitrite and ammonium formation.

Control of 0.2CaTiO3-0.8Li0.5Nd0.5TiO3 microwave dielectric ceramics by additions of Bi2Ti2O7

Ceramics of 0.2CaTi03-0.8Li 0.5 Nd 0.5 TiO 3 ) have been prepared by the mixed oxide route using additions of Bi 2 O 3 -2TiO 2 (up to 15 wt%). Powders were calcined 1100°C; cylindrical specimens were fired at temperatures in the range 1250-1325°C. Sintered products were typically 95% dense. The microstructures were dominated by angular grains 1-2 μm in size. With increasing levels of Bi 2 O 3 -2TiO 2 additions, needle and lath shaped second phases developed. For Bi 2 Ti 2 Ο 7 additions up to 5 wt%, the relative permittivity increased from 95 to 131, the product of dielectric Q value and measurement frequency increased from 2150 to 2450 GHz and the temperature coefficient of resonant frequency (τ f ) increased from -28pp/°C to +22pp/°C. A product with temperature stable τ f could be obtained at ∼2 wt% Bi 2 Ti 2 O 7 additions. For high levels of additives, there is minimal change in relative permittivity, the Qxf values degrade and τ f becomes increasingly negative.

THE COMPOSITION OF COEXISTING JAROSITE-GROUP MINERALS AND WATER FROM THE RICHMOND MINE, IRON MOUNTAIN, CALIFORNIA

Jarosite-group minerals accumulate in the form of stalactites and fi ne-grained mud on massive pyrite in the D drift of the Richmond mine, Iron Mountain, California. Water samples were collected by placing beakers under the dripping stalactites and by extracting pore water from the mud using a centrifuge. The water is rich in Fe 3+ and SO4 2– , with a pH of approximately 2.1, which is signifi cantly higher than the extremely acidic waters found elsewhere in the mine. Electron-microprobe analysis and X-ray mapping indicate that the small crystals (<10 � m in diameter) are compositionally zoned with respect to Na and K, and include hydronium jarosite corresponding to the formula (H3O)0.6K0.3Na0.1Fe 3+ 3(SO4)2(OH)6. The proton-microprobe analyses indicate that the jarosite-group minerals contain signifi cant amounts of As, Pb and Zn, and minor levels of Bi, Rb, Sb, Se, Sn and Sr. Speciation modeling indicates that the drip waters are supersaturated with respect to jarosite-group minerals. The expected range in composition of jarosite-group solid-solution in equilibrium with the pore water extracted from the mud was found to be consistent with the observed range in composition.

Trace elements accumulation in edible tissues of five sturgeon species from the Caspian Sea

This study is focused on twenty trace elements (Ag, Ba, Bi, Cd, Co, Cr, Cs, Cu, Ga, In, Mn, Mo, Pb, Rb, Sb, Sn, Sr, Ti, V, Zn) accumulation in muscles of five sturgeon species (Acipenser guldenstaedti, A. persicus, A. nudiventris, A. stellatus and Huso huso) from the southern part of the Caspian Sea. Moreover the relationships between some biological characteristics and the levels of the selected elements as well as inter-elemental relationships were assessed. The samples (10 specimens for each the five species) were collected from two important sturgeon fishery zones located in the Iranian part of the Sea in 2002. Concentrations of the elements were determined using ICP-MS. Only in the case of Cs could significant differences between two selected sampling areas be detected. There were significant differences in levels of Co, Ga, Rb, Sn, Ti, Pb and Bi in muscles of the species. Only in the case of Cd weight related differences among the species were found. The significant length dependent relationships were observed for Ga and Ba. Patterns of elements accumulation were assessed by statistical methods and compared to the other researches. In all the cases, the amounts of toxic trace elements (Cd, Cu, Pb and Zn) were markedly below the international guidelines for human consumption.

Influence of chemical bonds on Bi and Sb XPS shifts in Bi2S3and Sb2S3crystals

The paper presents the results of theoretical calculations of the shifts of Bi and Sb X-ray photoelectron spectra (XPS) due to chemical bond formation in Bi2S3 and Sb2S3 crystals. The energies of core levels of Bi, Sb, and S atoms are calculated by both the Hartree–Fock–Dirac (HFD) and Hartree–Fock methods and compared with the experimental values. The HFD method explains well the experimentally obtained spin–orbit splitting of the XPS. However, both theoretical methods give higher negative core level energies than their experimental values are.

Soil geochemical signature of a calciner site, Cornwall, SW England

Historical mining activity has led to significant anthropogenic contamination of areas of Cornwall. Arsenic-rich polymetallic ores were processed by heat treatment to remove the arsenic leaving residues of metalloids and metals. To investigate the long-term impact of arsenic ore processing and refining a derelict calciner site in West Cornwall was subjected to a study by soil sampling to test for contaminant levels of elements other than arsenic and determine their spatial distribution. Within the soil profile, levels of Cu, Zn, Pb, Bi, W,U, Ga, and Cd are elevated above background concentrations. SEM examination shows that there are complex particulate grains of metals and metalloids. Statistical examination shows significant correlation between metals and arsenic as well as correlation between metals. The geochemistry of the residues indicates that the feedstock came predominantly from the Camborne–Redruth orefield. Contamination was mainly from fugitive dusts and a distinct geochemical signature is apparent in the soil surrounding the old industrial site.

Citrate enhances the protective effect of orally administered bismuth subnitrate against the nephrotoxicity of cis-diamminedichloroplatinum.

Attenuation of the renal toxicity of cis-diamminedichloroplatinum (CDDP) is important in the use of this effective but cytotoxic anticancer agent. We have previously shown that the renal toxicity of CDDP can be efficiently reduced by the induction of metallothionein (MT) by preadministration of bismuth compounds in mice. Bismuth subnitrate (BSN) is used as an antigastric ulcer agent and as an antidiarrheic agent, and is suitable for inducing MT in the kidney in cancer patients. However, due to the low absorption rate of Bi from the gastrointestinal tract, the efficacy of BSN in inducing renal MT is low. In the present study, we examined the effects of citrate as a vehicle for oral administration of BSN on the tissue distribution of Bi and induction of MT in the kidneys and tumors in mice inoculated with Meth-A fibrosarcoma. Renal levels of MT and Bi were markedly increased in the mice given BSN dissolved in citrate solution compared with those given BSN suspended in saline. On the other hand, the use of citrate increased Bi accumulation in the tumor only slightly and did not increase tumor MT levels. Administration of BSN with citrate efficiently depressed the renal toxicity of CDDP, but did not affect its antitumor activity. Since both BSN and citrate are used clinically as pharmaceuticals, the combination regimen of BSN and citrate may be readily applicable as a countermeasure against the adverse side effects of CDDP without affecting its antitumor activity.

The microwave dielectric properties of CaTiO3–Li0.5Nd0.5TiO3 ceramics prepared with Bi2Ti2O7 additions

Abstract Ceramics of 0.4CaTiO 3 –0.6Li0.5Nd 0.5 TiO 3 (0.4CT–0.6LNT) have been prepared by the mixed oxide route using additions of Bi 2 O 3 –2TiO 2 (up to 30 wt.%). Powders were calcined 1100 °C; cylindrical specimens were fired at temperatures in the range 1175–1275 °C. Sintered products were typically 90–95% dense. The microstructures were dominated by angular grains typically 2 μm in size. With increasing levels of Bi 2 O 3 –2TiO 2 additions, needle and then lath shaped second phases developed. Microwave dielectric properties of 0.4CT–0.6LNT at 2.1 GHz were 126, 2600 GHz and 127 ppm/°C for e r , Qxf and τ f , respectively. The use of bismuth additions caused the relative permittivity to increase (to a maximum value of 150), the Qxf to steadily decrease (minimum value of 1000GHz) and τ f to decrease almost linearly towards zero.

X-Ray Photoelecton Spectra and Electronic Structure of Bi2S3 Crystals

The paper presents the X-ray photoelectron spectra (XPS) of the valence band and core levels of the semiconductive Bi 2 S 3 single crystal, which shows anomalies in various physical properties and weak phase transitions without change of symmetry. The XPS were measured with monochromatized Al K a radiation in the energy range 0-1400 eV and the temperature range 160-460 K. The valence band is located 0.55-6.5 eV below the Fermi level and shows non-linear dependence on temperature. Experimental energies of the valence band and core levels are compared with the results of theoretical ab initio calculations of the molecular model of the Bi 2 S 3 crystal. The chemical shifts in the Bι 2 S 3 crystal for the Bi and S states are obtained. Results revealed the origin of a weak polarity of the crystals at room temperature, which results in anomalies in the physical properties, and shifts the Fermi level and all the electronic spectrum.

Arsenic, Sb and Bi contamination of soils, plants, waters and sediments in the vicinity of the Dalsung Cu–W mine in Korea

The objective of this study is to investigate environmental contamination derived from metalliferous mining activities. In the study area, the Dalsung Cu–W mine, soils, various crop plants, stream waters, sediments and particulates were sampled in and around the mine and analyzed for As, Sb and Bi by ICP-AES with a hydride generator. In addition, soil pH, cation exchange capacity, loss-on-ignition and soil texture were also measured. Concentrations of As, Sb and Bi in surface soils sampled in the mine dump sites averaged 2500, 54 and 436 μg g −1, respectively. Relatively lower concentrations, however, were found in soils from alluvial and high land sites and household garden sites. Arsenic, Sb and Bi contents in plant samples varied depending upon their species and parts, with higher concentrations in spring onions, soybean leaves and perilla leaves and lower levels in red peppers, corn grains and jujube grains. These results confirm that elemental concentrations in plant leaves are much higher than those in plant grain. Elevated levels of As, Sb and Bi were also found in stream sediments sampled in the vicinity of the mine and decreased with distance from the mine. Concentrations in stream water samples ranged from 0.8 to 19.1 μg As l −1 and from 0.3 to 8.4 μg Bi l −1; all the samples contained less than 1.0 μg Sb l −1. Because of very low particulate loading at the time of sampling, the metal contents in particulates were very low (<8.2 μg As l −1,<0.22 μg Sb l −1 and 2.8 μg Bi l −1. This may be mainly due to the low solubility of those elements under moderately acidic and oxidizing conditions of the mining area.

Antibacterial Effect of Fermented Milk ContainingBifidobacterium breve, Bifidobacterium bifidumandLactobacillus acidophilusagainst IndigenousEscherichia coliInfection in Mice

Injection of a lethal dose of 5- uorouracil (400 mg/kg) into mice induced an extraordinary increase in the levels of endogenous Escherichia coli in the intestine, systemic translocation of the bacteria to the liver, and loss of body weight. Daily administration of a fermented milk (0.2 ml) containing Bifidobacterium breve strain Yakult, B. bifidum strain Yakult, and Lactobacillus acidophilus strain Yakult (10 8.5-9.5 CFU/ml) to mice for 7 days before and 9 days after 5-FU prevented the endogenous infection, whereas treatment of mice with water or unfermented milk did not lead to any signi. cant protection against the infection. The levels of indigenous bi. dobacteria in the intestinal contents decreased markedly with time after injection of 5-FU in the control groups, and this was associated with a marked decrease in the concentration of total short-chain fatty acids (SCFAs) and an increase in the pH on day 10 after 5-FU administration (pH: 7.3, SCFAs: 40 mM). Administration of fermented milk maintained the concentrations of the total SCFAs at the same levels as before 5-FU administration (120 mM) throughout the experimental period. The pH and concentration of acetic acid in the intestinal contents (pH: 6.7, AA: 90 mM) were found to suppress in vitro growth of an indigenous strain of E. coli These results suggest that the protective effect of oral administration of fermented milk against the endogenous E. coli infection resulted from prevention of any abnormal increase in E. coli levels via normalization of the 5-FU-induced disruption of the intestinal environment. Keywords : acetic acid, Bi. dobacteria, E. coli , fermented milk, infection, mouse, short chain fatty acid (SCFA).

Preparation and characterization of compounds in the BaBiO3–Ba(Ce1-xGdx)O3-x/2 system

The structure, nonstoichiometry, and electrical conductivity of compositions in the BaBiO3– Ba(Ce1-xGdx)O3-x/2 system have been investigated in an attempt to prepare new mixed (ionic-electronic) conducting oxides. The substitution of Bi into Ba(Ce1-xGdx)O3-x/2 decreases the concentration of oxygen-ion vacancies, and the effective negative charge of the Gd dopant is compensated by the mixed valence of Bi (3+, 5+). For low Bi contents a decrease in ionic conductivity decreases the overall conductivity; however, higher levels of Bi introduce significant electronic conductivity, and for Ba(Bi0.5Ce0.5)O3, σtotal ≈ 1 S/cm at 800 °C in air. Compositions in the Ba(Bi0.5Ce0.5-xGdx)O3 pseudobinary system undergo a B-cation order-disorder transformation at 1300–1350 °C for x = 0.5 and at ≈1250 °C for x = 0.4; all other compositions retain a disordered B-site arrangement. While these disordered perovskites exhibit oxygen nonstoichiometry under reducing conditions at elevated temperatures, with the extent of reduction decreasing with increasing Gd content, their ordered counterparts remain close to stoichiometry. The electronic conductivities of this pseudobinary could be fitted to a “band-type” model, and, despite the presence of oxygen vacancies for the lower values of x, no significant ionic conductivity was observed.

Trace Element Analysis of Natural Gold by Laser Ablation ICP‐MS: A Combined External/Internal Standardisation Approach

For the trace element analysis of gold by laser ablation ICP‐MS, external calibration samples of differing matrix composition have been used in previous studies. Data presented here suggest that even for calibration samples and unknowns with closely‐matched matrices, discrepancies arise due to variations in the coupling behaviour of the laser with the sample at different power deliveries, and can lead to erroneous trace element determinations. Internal standardisation for gold is complicated because Au and Ag, the most common major elements, do not have minor isotopes that can be used as internal standards. This problem was overcome for natural gold samples by using an external calibration sample only for the major elements Au and Ag, then defocussing the ion path and using 107Ag in each sample as an internal standard against which μg g‐1 levels of Te, Sb, Hg, Bi, and Cu were determined. The results suggest that trace elements can occupy lattice sites in gold rather than occurring only as micro‐inclusions of other phases. The analytical approach taken here may be used in trace element analysis where adequate external calibration samples are not readily available.

Vitamin status and mitochondrial DNA mutations in patients with incomplete recovery from an epidemic optic neuropathy in Cuba

From 1991 until early 1994, nearly 51,000 Cubans were afflicted by an outbreak of optic neuropathy (ON) and peripheral neuropathy (PN). Nutritional deficiencies, toxins, genetic factors, and infectious agents have been investigated for their pathogenic role. Previously, we reported two probands harboring Leber's hereditary optic neuropathy (LHON)-associated mitochondrial (mtDNA) mutations. We examined nine additional patients, selected by Cuban physicians, because of evidence of incomplete recovery from ON, and studied the role of LHON mutations and vitamin status. All of the patients had received multivitamin therapy for varying time. We performed ophthalmological and neurological examinations, analyzed blood levels of vitamins Bi, B6, and B12, and screened leukocyte DNA for primary mtDNA mutations associated with LHON using standard assays. Three of the nine patients had low blood vitamin levels, indicating that vitamin deficiencies might be associated with persistent ON in some Cuban patients. None of ...

Application of chemically modified probe-atomic absorption spectrometry (CMPAAS)-I. Determination of Bi in copper alloy and lead by trioctylphosphine oxide-coated tungsten probe-AAS

A trioctylphosphine oxide (TOPO) coated tungsten probe has been prepared and used for the determination of Bi and the μg/g level in copper alloy and lead. Bismuth is preconcentrated on the probe which is placed in a graphite-cup furnace for AA determination of bismuth. The method has good sensitivity and minimises analysis time. Microgram per gram levels of Bi can be determined with good precision and accuracy.

Platinum-group element and gold contents in the Skouries porphyry copper deposit, Chalkidiki Peninsula, northern Greece

The Skouries porphyry copper deposit is located in the eastern Chalkidiki peninsula, northern Greece. Along with several other porphyry copper occurrences, this deposit establishes the northeastern part of the Servomacedonian zone as a porphyry copper region. Amphibolite, mica schist, and two-mica gneiss are the predominant rock types exposed in the Skouries area. These rocks have been intruded by the Skouries porphyry stock, which is of subalkaline composition and is Tertiary in age (18 Ma). The Skouries porphyry intrusion and the surrounding country rocks are strongly fractured and intensely altered by hydrothermal fluids. In addition to intense silicification, a prominent alteration type is potassic, whereas phyllic and propylitic types are less common.Mineralization mainly includes chalcopyrite, pyrite, bornite, chalcocite, and magnetite in the form of veins, stockworks, and disseminations. Native gold and electrum commonly are present as small inclusions in chalcopyrite. Although lateral zoning is not defined clearly, a vertical zoning in terms of both metal mineralogy and overall metal content is apparent. A zone of oxidation (azurite-malachite) covers the upper part of the ore and is underlain by a zone of reduced rock rich in covellite and chalcocite, which in turn is underlain by the most important ore type, including a chalcopyrite-pyrite-bornite-magnetite assemblage.Both weakly and intensively altered porphyry samples from the deposit were analyzed for major oxides, trace elements, and all platinum-group elements (PGE). The stock exhibits high levels of Cu, Au, Ag, B, Bi, Co, Se, and Te. Barium and Sr contents are also high while Rb is low, resulting thereby in high K/Rb and low Rb/Sr ratios. Palladium concentrations range from less than 2 to 480 ppb. Ruthenium content ranges from 8 to 41 ppb and Pt from 2 to 10 ppb. Osmium, Ir, and Rh content is below detection limit. The average Au/Ag ratio is 0.87, which is consistent with the range of several worldwide porphyry copper deposits.On the basis of factor analysis of selected geochemical data, a strong positive interelement correlation (r > or = 0.83) between Au, Ag, Pd, nd Te coupled with their association with silica appears to support a correlation of these precious metals with silicification rather than potassic-type alteration. Such a relationship may suggest similar behavior of these metals and a common origin. A positive correlation of Cu with iron (r = 0.86), which is consistent with the association of chalcopyrite with magnetite, and the low correlation of Te and Pd with Cu may suggest that these metals and, to a lesser extent, copper have been redistributed during a late stage of evolution of the Skouries porphyry system. Furthermore, the close association of Te with precious metals, combined with the relatively low temperature for telluride minerals stability, may indicate that at least partly precious metal tellurides have been formed in a relatively shallow and less hot environment.

Expression of HPCA-1 and HLA-DR antigens on growth factor- and stroma-dependent colony forming cells.

The expression of HLA-DR and HPCA-1 antigens (recognized by the L243 and BI.3C5 antibodies respectively) on adult human bone marrow cells was examined by fluorescence activated cell sorting and colony assays. Nearly all the (day 14) lineage restricted and multipotential colony forming cells analysed in methylcellulose cultures in the presence of added growth factors express HLA-DR and HPCA-1 determinants. Two colour cell sorting reveals that the lineage restricted HLA-DR positive progenitors express variable levels of BI.3C5 positivity whereas most of the multipotential progenitors, the multi-CFC or CFU-GEMM, are highly BI.3C5 positive. The isolated HLA-DR and BI.3C5 positive populations also contain haemopoietic precursors which adhere to and form colonies on pre-formed stromal layers. Thus, haemopoietic progenitors assayed in both types of culture system can be analysed and enriched by simultaneous two-colour sorting using anti-HLA-DR and BI.3C5 monoclonal antibodies. Similarities in the antigenic phenotype of such cells, however, precludes the use of these reagents for segregating growth factor-dependent from stroma-dependent progenitors.