Increase in the calcium content of cardiac tissue after postfixation with osmium tetroxide

Measurements of environmental lead contamination and human exposure

The importance of accurate measurements of environmental lead exposure and toxicity is substantiated by analyses documenting the global contamination of the biosphere with industrial lead and the pervasiveness of measurable lead toxicity in human populations. Those data demonstrating environmental lead contamination and toxicity have, in part, led to regulations that limit the amount of lead in some products (e.g., paint, solder, and gasolines) in many industrialized countries. These regulations have resulted in a substantial reduction in some lead discharges to the environment. In spite of these reductions, current environmental lead levels are still often more than 10-fold, and sometimes more than 10,000-fold, higher than natural levels. Further, environmental lead concentrations are expected to remain elevated for a protracted period due to continued emissions of relatively large amounts of industrial lead to the environment and the persistence of contaminant lead in the environment. Discharges of contaminant lead have resulted in increases in organism and human lead levels comparable to increases documented in environmental matrices, as indicated by a recent estimate of the natural level of lead in blood of preindustrial humans (0.016 microgram/dL or 0.8 nM). This estimate is 175-fold lower than average blood lead levels in the United States (2.8 micrograms/dL or 140 nM) and 600-fold lower than the recently (1991) revised Centers for Disease Control (CDC) action level of concern for early toxic effects in children (10 micrograms/dL or 480 nM). The significance of these comparisons to public health is corroborated by numerous studies suggesting that there may be no lower threshold for sublethal toxicity in contemporary (i.e., lead-contaminated) humans. Those data also indicate that environmental lead concentrations that were previously considered innocuous may be deleterious to human health. It is apparent that the extent of sublethal lead toxicity in humans may be best addressed by studies that consider control populations possessing natural (i.e., preindustrial) lead burdens, as well as state-of-the-art, trace-metal-clean techniques and advanced instrumentation. Trace-metal-clean techniques are required to prevent the inadvertent lead contamination of samples, which has plagued many previous analyses of environmental and human lead levels. Advanced instrumentation is required to provide the sensitivity, accuracy, and precision that are needed to quantify the sublethal effects of lead concentrations at environmental levels of exposure. Fortunately, methodologies utilizing these advancements are now capable of addressing many of the important issues (e.g., lead biomolecular speciation, low exposure effects) in environmental and human lead toxicology.

Electron spectroscopic study (ESI, EELS) of Nanoplast-embedded mammalian lung

The potential of Nanoplast melamine resin embedding for the study of mammalian lung parenchyma was examined by means of electron spectroscopic imaging (ESI) and electron energy-loss spectroscopy (EELS). Samples were either fixed with glutaraldehyde-paraformaldehyde or glutaraldehyde-tannic acid, or were directly transferred to the embedding medium without prior fixation. Organic dehydrants, as well as fixatives containing heavy metals and stains, were omitted. A very high level of ultrastructural detail of chromatin, ribosomes, mitochondria and plasma membranes was achieved by ESI from the Nanoplast-embedded samples. The most prominent gain in ultrastructural detail was achieved when moving from an energy loss just below the L2,3 edge of phosphorus at 132 eV to an energy loss just beyond this edge. This reflects the prominent P L2,3 edge observed by EELS of Nanoplast-embedded samples in comparison with conventionally processed samples. Thus, taking into account possible sectioning artefacts, excellent heterochromatin images which rely on the phosphorus distribution can be obtained from Nanoplast-embedded samples by computer-assisted analysis of electron spectroscopic images. In this respect glutaraldehyde-paraformaldehyde fixation is preferable to glutaraldehyde-tannic acid fixation because the presence of silicon, revealed by EELS, in tannic-acid-fixed samples may introduce artefacts in phosphorus distribution images obtained by the three-window method because of the close proximity of the L2,3 edges of silicon and phosphorus.

Biological applications of electron probe microanalysis in France

The contribution of French science to the field of biological X-ray microanalysis is reviewed. The main analytical microscopy centers are listed, and their methods and main results are summarized.