Using qualitative backscattered electron (BSE) imaging and quantitative energy dispersive X-ray (EDX) spectroscopy, some investigators have concluded that cement (reversal) lines located at the periphery of secondary osteons are poorly mineralized viscous interfaces with respect to surrounding bone. This conclusion contradicts historical observations of apparent highly mineralized (or collagen-deficient) cement lines in microradiographs. Such conclusions, however, may stem from unrecognized artifacts that can occur during scanning electron microscopy. These include specimen degradation due to high-energy beams and the sampling of electron interaction volumes that extend beyond target locations during EDX analysis. This study used quantitative BSE imaging and EDX analysis, each with relatively lower-energy beams, to test the hypothesis that cement lines are poorly mineralized. Undemineralized adult human femoral diaphyses (n ϭ 8) and radial diaphyses (n ϭ 5) were sectioned transversely, embedded in polymethyl methacrylate, and imaged in a scanning electron microscope for BSE and EDX analyses. Unembedded samples were also evaluated. Additional thin embedded samples were stained and evaluated with light microscopy and correlated BSE imaging. BSE analyses showed the consistent presence of a bright line (higher atomic number) coincident with the classical location and description of the cement line. This may represent relative hypermineralization or, alternatively, collagen deficiency with respect to surrounding bone. EDX analyses of cement lines showed either higher Ca content or equivalent Ca content when compared to distant osteonal and interstitial bone. These data reject the hypothesis that cement lines of secondary osteons are poorly mineralized.

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Dust storms in Asia's interior deserts loft immense quantities of continental crust that are blown over the North Pacific Ocean every year. The transported mineral aerosol is first lofted and then experiences mixing and fallout during the transport. Its elemental signature is no longer that of bulk soil. The concentration for many elements is greater in transported crust compared to bulk soil due to a difference in mineralogy of the small crustal particle. Small particles are defined as those below 100 μm in diameter. The elements Al, Mg, Ca and Na do not experience an internal concentration change with particle size. Many of the elements in the MLO mineral aerosol have concentrations that are greater than 1.5 times that of bulk soil. Iron, an important biological agent, has twice the concentration in the MLO mineral aerosol than in bulk soil. The elemental to Al concentration ratios observed are consistent, implying that the transported crustal material is below 20 μm in diameter.

Aerosol samples were collected at the Mauna Loa Observatory in Hawaii from February 1979 to May 1985. The samples were analyzed via instrumental neutron activation analysis (INAA) for up to 47 elements and via ion chromatography for sulfate. The data are dominated by crustal dust that arrives via long‐range transport from Asia each spring, thus creating a “dust season.” Of the 47 elements detected, 37 have a notably higher mass average during the dust season. The data record is explored using enrichment factors, principal component analysis, and chemical mass balances (receptor modeling). The crustal material accounts for 60–70% of the overall aerosol mass during dust seasons, yet only 15–20% during nondust seasons. It is by far the largest contributor to the natural variation dominating the principal component analysis by describing greater than 60% of the overall variance. Particulate sulfate is another major component accounting for 10–40% of the aerosol mass during dust seasons and 60–75% of the mass during nondust seasons. Particulate sulfate can be derived from crustal material and sea salt. Anthropogenic activity also can produce particulate sulfate or its precursors that can adhere to the surface of crustal material that travels over a polluted area. Minor components in the downslope winds are marine sea‐salt aerosol contributing less than 3% of the aerosol mass during the dust season and 5–6% during the nondust season. Local basalt is considered to contribute less than 2% during the dust season and 3–4% during the nondust season. (Carbon mass is not determined and therefore no carbon‐based aerosols such as soot or organic aerosols are considered in the total aerosol mass.)

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Summary:Energy-dispersive x-ray (EDX) spectroscopy and backscattered electron (BSE) imaging are finding increased use for determining mineral content in microscopic regions of bone. Electron beam bombardment, however, can damage the tissue, leading to erroneous interpretations of mineral content. We performed elemental (EDX) and mineral content (BSE) analyses on bone tissue in order to quantify observable deleterious effects in the context of (1) prolonged scanning time, (2) scan versus point (spot) mode, (3) low versus high magnification, and (4) embedding in poly-methylmethacrylate (PMMA). Undemineralized cortical bone specimens from adult human femora were examined in three groups: 200× embedded, 200× unembedded, and 1000× embedded. Coupled BSE/EDX analyses were conducted five consecutive times, with no location analyzed more than five times. Variation in the relative proportions of calcium (Ca), phosphorous (P), and carbon (C) were measured using EDX spectroscopy, and mineral content variations were inferred from changes in mean gray levels ("atomic number contrast") in BSE images captured at 20 keV. In point mode at 200×, the embedded specimens exhibited a significant increase in Ca by the second measurement (7.2%, p < 0.05); in scan mode, a small and statistically nonsignificant increase (1.0%) was seen by the second measurement. Changes in P were similar, although the increases were less. The apparent increases in Ca and P likely result from decreases in C: -3.2% (p < 0.05) in point mode and -0.3% in scan mode by the second measurement. Analysis of unembedded specimens showed similar results. In contrast to embedded specimens at 200×, 1000× data showed significantly larger variations in the proportions of Ca, P, and C by the second or third measurement in scan and point mode. At both magnifications, BSE image gray level values increased (suggesting increased mineral content) by the second measurement, with increases up to 23% in point mode. These results show that mineral content measurements can be reliable when using coupled BSE/EDX analyses in PMMA-embedded bone if lower magnifications are used in scan mode and if prolonged exposure to the electron beam is avoided. When point mode is used to analyze minute regions, adjustments in accelerating voltages and probe current may be required to minimize damage.

Summary: Electron beam interactions with specimens in the scanning electron microscope (SEM) can lead to increased surface temperatures and damage. These changes may have significant consequences in the analysis of bone tissue. An investigation was performed to measure the surface temperature changes associated with the electron beam on a thermocouple with systematic variations in operating conditions. Probe currents, magnifications, and accelerating voltages were incrementally adjusted to measure the temperature changes and to make assessments for determining optimal operating conditions for the SEM in future analyses of bone tissue. Results from this study suggest that thermal effects were minimal at lower accelerating voltages (< 20 kV), lower probe currents (< 10 nA), and lower magnifications, but surface damage may still occur during the analysis of bone tissue.

Marine material contributes only a third of the trace metal mass compared to the crustal contribution. Anthropogenic and biogenic material usually contribute less than 5% of the trace element mass (excluding carbon and sulfate). Sulfate, which was measured by ion chromatography for part of the period, contributes a mass similar to crustal mineral; however, it does not have a strong seasonal pattern. A pollution episode in 1989 increased the budget of several elements by an order of magnitude or more. The trace acidic gas data support the conclusion that marine material in the free troposphere has been weathered, leading to a chlorine depletion in marine particles.