John W. Drexler

Evaluation of Small Arms Range Soils for Metal Contamination and Lead Bioavailability

Although small arms ranges are known to be contaminated with lead, the full extent of metal contamination has not been described, nor has the oral bioavailability of lead in these soils. In this work, soil samples from ranges with diverse geochemical backgrounds were sieved to <250 microm and analyzed for total metal content. Soils had consistently high levels of lead and copper, ranging from 4549 to 24 484 microg/g and 223 to 2936 microg/g, respectively, while arsenic, antimony, nickel, and zinc concentrations were 100-fold lower. For lead bioavailability measurements, two widely accepted methods were used: an in vivo juvenile swine relative bioavailability method measuring lead absorption from ingested soils relative to equivalent lead acetate concentrations and an in vitro bioaccessibility procedure which measured acid-extractable lead as a percent of total lead in the soil. For eight samples, the mean relative bioavailability and bioaccessibility of lead for the eight soils was about 100% (108 +/- 18% and 95 +/- 6%, respectively) showing good agreement between both methods. Risk assessment and/or remediation of small arms ranges should therefore assume high bioavailability of lead.

Record of middle Pleistocene climate change from Buck Lake, Cascade Range, southern Oregon—Evidence from sediment magnetism, trace-element geochemistry, and pollen

Comparison of systematic variations in sediment magnetic properties to changes in pollen assemblages in middle Pleistocene lake sediments from Buck Lake indicates that the magnetic properties are sensitive to changes in climate. Buck Lake is located in southern Oregon just east of the crest of the Cascade Range. Lacustrine sediments, from 5.2 to 19.4 m in depth in core, contain tephra layers with ages of ≈300–400 ka at 9.5 m and ≈400–470 ka at 19.9 m. In these sediments magnetic properties reflect the absolute amount and relative abundances of detrital Fe-oxide minerals, titanomagnetite and hematite. The lacustrine section is divided into four zones on the basis of magnetic properties. Two zones (19.4–17.4 m and 14.5–10.3 m) of high magnetic susceptibility contain abundant Fe oxides and correspond closely to pollen zones that are indicative of cold, dry environments. Two low-susceptibility zones (17.4–14.5 m and 10.3–5.3 m) contain lesser amounts of Fe oxides and largely coincide with zones of warm-climate pollen. Transitions from cold to warm climate based on pollen are preceded by sharp changes in magnetic properties. This relation suggests that land-surface processes responded to these climate changes more rapidly than did changes in vegetation as indicated by pollen frequencies. Magnetic properties have been affected by three factors: (1) dissolution of Fe oxides, (2) variation in heavy-mineral content, and (3) variation in abundance of fresh volcanic rock fragments. Trace-element geochemistry, employing Fe and the immobile elements Ti and Zr, is utilized to detect postdepositional dissolution of magnetic minerals that has affected the magnitude of magnetic properties with little effect on the pattern of magnetic-property variation. Comparison of Ti and Zr values, proxies for heavy-mineral content, to magnetic properties demonstrates that part of the variation in the amount of magnetite and nearly all of the variation in the amount of hematite are due to changes in heavy-mineral content. Variation in the quantity of fresh volcanic rock fragments is the other source of change in magnetite content. Magnetic-property variations probably arise primarily from changes in peak runoff. At low to moderate flows magnetic properties reflect only the quantities of heavy minerals derived from soil and highly weathered rock in the catchment. At high flows, however, fresh volcanic rock fragments may be produced by breaking of pebbles and cobbles, and such fragments greatly increase the magnetite content of the resulting sediment. Climatically controlled factors that would affect peak runoff levels include the accumulation and subsequent melting of winter snow pack, the seasonality of precipitation, and the degree of vegetation cover of the land surface.Our results do not distinguish among the possible contributions of these disparate factors.

An In Vitro Method for Estimation of Arsenic Relative Bioavailability in Soil

This report summarizes the results of a study to develop an in vitro bioaccessibility (IVBA) extraction technique for estimating the relative bioavailability (RBA) of arsenic (As) in soil. The study was implemented in several steps. In step 1, key variables in the extraction protocol were identified. In step 2, 21 different extraction conditions were tested on 12 different soils with reliable RBA values measured in swine or monkeys to identify which yielded useful in vivo–in vitro correlations (IVIVC). In step 3, three extraction conditions were evaluated using 39 different test soils to make a final selection of the best IVIVC. In step 4, the within- and between-lab reproducibility of the extraction method was examined. The optimum IVIVC model for swine utilized a pH 1.5 IVBA extraction fluid, with an R 2 value of .723. For monkeys, the optimum IVIVC model was obtained using a pH 7 IVBA extraction fluid that contained phosphate, with an R 2 value of .755. Within-lab precision of IVBA results was typically less than 3%, with an average of 0.8% for all 4 labs. Between-lab variation in mean IVBA values was generally less than 7%, with an overall average of 3%. The principal advantages of this IVBA method compared to other in vitro methods described in the literature are that (1) the fluids and extraction conditions are simple, (2) the results have been calibrated against a larger data set than any other method, and (3) the method has been demonstrated to be reproducible both within and between labs.

Solubility enhancement of seven metal contaminants using carboxymethyl-β-cyclodextrin (CMCD)

Carboxymethyl-beta-cyclodextrin (CMCD) has been suggested as a complexing agent for remediation of sites co-contaminated with metals and organic pollutants. As part of an attempt to construct a geochemical complexation model for metal-CMCD interactions, conditional formation constants for the complexes between CMCD and 7 metal ions (Ba, Ca, Cd, Ni, Pb, Sr, and Zn) are estimated from experimental data. Stable metal concentrations were reached after approximately 1 day and estimated logarithmic conditional formation constants range from -3.2 to -5.1 with confidence intervals within +/-0.08 log units. Experiments performed at 10 degrees C and 25 degrees C show that temperature affects the solubility of the metal salts but the strength of CMCD-metal complexes are not affected by this temperature variation. The conditional stability constants and complexation model presented in this work can be used to screen CMCD as a potential remediation agent for clean-up of contaminated soil and groundwater.

Composition dependence of the superconducting properties of the Tl-Ba-Ca-Cu-O system

Abstract A series of superconducting samples with nominal composition Tl 2 Ba 2 Ca n -1 Cu n O 2 n +4 (1≤ n ≤11) have been prepared by a two-step method using barium nitrate (instead of barium oxides or barium carbonate). The phase analysis and structural analysis were performed by X-ray diffraction and an electron microprobe. The four-probe resistance and AC susceptibility measurements show that all the samples are superconducting with T c above 105 K except the n =1 sample, which has a T c of 88 K. The highest T c ( T c (M)=124 K) in this series is obtained in the n =5 sample. It is found that there is a correlation between T c and lattice parameter a of the 2223 phase. T c increases when lattice parameter a decreases. Several new phases are found by the microprobe analysis. The reaction route and the stability of the samples are also discussed.

Single crystal growth of Tl-based superconductors

Abstract Large single crystals of Tl 2 Ba 2 CuO 6 and Tl 2 Ba 2 CaCu 2 O 8 superconductors were grown by a two-step self-flux process. In the first step, a mixture of Tl 2 O 3 , BaO (and CaO for 2212 crystals) and CuO was heated at 940°C for about ten minutes to form bulk superconductors. In the second step, the bulk compound was re-ground, re-pelletized and placed into an Al 2 O 3 crucible which was then sealed. The sealed crucible was heated up to above melting point of the bulk superconductor. The crystals were grown as the temperature cooled down slowly. Crystals are plate-like with in-plane crystal size as large as 12 mmx8 mm and the thickness range from 20 μm to 0.8 mm. X-ray diffraction experiments, SEM and other chemical analysis results have shown the crystals to be of high quality and chemically uniform.

Pyrithione and 8-hydroxyquinolines transport lead across erythrocyte membranes

Acute and chronic lead poisoning remains a significant health problem. Although chelating agents can bind to plasma lead, they cannot cross cell membranes where the total body lead burden resides, and are thus inefficient at reducing the total body lead burden. Recently, calcium and sodium ionophores have been shown to transport lead across cell membranes providing a novel method for reducing total body lead stores. We recently found that clioquinol, an 8-hydroxyquinoline derivative, can act as a zinc ionophore. We postulated that zinc ionophores might also be able to transport lead across biological membranes. To study this, we loaded lead in vitro into human erythrocytes and then studied the ability of zinc ionophores to transport lead into the extracellular space, where it was trapped with a lead chelator. Using inductively coupled plasma mass spectrometry (ICP-MS), we found that several 8-hydroxyquinoline derivatives, as well as the zinc and sodium salts of pyrithione (N-hydroxypyridine-2-thione), reduced erythrocyte lead content. The water-soluble compound, sodium pyrithione, was able to reduce lead in citrated whole blood, without partitioning into the erythrocytes. These results indicate that two classes of zinc ionophores can transport lead across a biological membrane, and they confirm that these ionophores are not cation-specific. Lead ionophores may prove useful in mobilizing lead into the extracellular space, thereby improving the efficacy of chelation therapy, in vivo or ex vivo.

Tl‐Ba‐Ca‐Cu‐O superconducting thin films with postdeposition processing using Tl‐containing thin films as Tl source

We describe a new method of processing Tl‐Ba‐Ca‐Cu‐O (TBCCO) superconducting thin films. In this method, two identical elemental multilayer films containing Tl layers were prepared using an electron‐beam deposition technique. The thin‐film samples were then placed in face‐to‐face contact in a quartz crucible and heat treated at 740 °C for 10 min in flowing air. The x‐ray microanalysis of the bottom sample indicates promising results for obtaining the desired chemical composition. Random characterization from different sections of the sample showed that the microanalysis values had less scatter than those for samples prepared using the usual bulk postdeposition method. The average chemical composition of the 13 points obtained from the random section is Tl1.8Ba1.8Ca1.9Cu2.0Ox. However, oxygen analysis showed that the concentration of oxygen is low and poorly distributed, presumeably attributable to the low oxygen flow. This method has several advantages over the conventional Tl‐O vapor processing using pur...