Tracer Methods Research Articles

Spinal Nerve Innervation to the Sonic Muscle and Sonic Motor Nucleus in Red Piranha, Pygocentrus nattereri (Characiformes, Ostariophysi)

The red piranha, Pygocentrus nattereri, produces sounds by rapid contractions of a pair of extrinsic sonic muscles. The detailed innervation pattern of the sonic muscle of the red piranha was investigated. The sonic muscle is innervated by branches (sonic branches) of the third (S3so), fourth (S4so), and fifth (S5so) spinal nerves. The average total number of nerve fibers contained in the right sonic branches (n = 5; standard length, SL, 71–85 mm) was 151.8 (standard deviation, SD, 28.3). The occipital nerve did not innervate the sonic muscle. The sonic motor nucleus (SMN) in the piranha was identified by tracer methods using wheat germ agglutinin-conjugated horseradish peroxidase; labeled sonic motor neurons were only observed on the side ipsilateral to the sonic muscle injected with the tracer. In the transverse sections, the labeled sonic motor neurons were located in the dorsal zone (mainly large and medium neurons) and in the ventral zone (mainly small neurons) of the ventral horn. In the horizontal sections, the labeled neurons formed a rostrocaudally elongated SMN from the level of the caudal part of the second spinal nerve root to the intermediate region between the fifth and sixth spinal nerve roots. The average number of the labeled neurons (n = 5; SL, 64–87 mm) was 152.6 (SD, 7.3). We conclude that the sonic muscles of the piranha are innervated by approximately 300 sonic motor neurons located only in the spinal cord.

ヒトが一日に必要とするアミノ酸の量をどのようにして推定するか？

Amino acids are constituents of protein that is the major functional and structural component of all the cells of the body, and are required for health and reproduction. In the nutritional classification, the amino acids are categorized into two groups, essential (indispensable) and non-essential (dispensable). The essential amino acids (L-histidine, L-isoleucine, L-leucine, L-lysine, L-methionine, L-phenylalanine, L-threonine, L-tryptophan, and L-valine) have carbon skeletons that cannot be synthesized from simpler molecules in animals, and therefore must be provided in the diet. The earlier methodologies for determining amino acid requirements, which was based on nitrogen balance, were criticized because of their experimental design, but now essential amino acid requirements for adult humans are estimated by isotopic tracer methods and linear regression analysis. This article reviews recent advances in studies on amino acid requirements estimated by using the 13C-labeled amino acid oxidation method, isotope ratio mass spectrometry (IRMS) for the measurement of 13CO2-12CO2 ratio in expired breath CO2 and gas chromatography-mass spectrometry (GC/MS) for the measurement of isotopic enrichment of the precursor in 13CO2 production.

Evidence for the Usefulness of in vitro Dialyzability, Caco-2 Cell Models, Animal Models, and Algorithms to Predict Zinc Bioavailability in Humans

Low bioavailability of zinc in certain diet types may contribute to zinc deficiency and its consequences in populations. As a result, several experimental models including animal models, in vitro dialyzability models, and Caco-2 cells, have been used to study these factors and estimate their impact on human zinc absorption. For the most part, consistency has been observed between the latter models and human absorption studies to identify factors that enhance or inhibit zinc bioavailability. However, dialyzability methods are limited to modeling luminal interactions among the factors as they affect zinc availability while Caco-2 cells can model luminal effects and uptake by intestinal cells. Neither animal nor in vitro methods can predict the magnitude of zinc absorption at the level of the human organism. Caco-2 cells will be useful models for understanding the mechanisms of intestinal zinc absorption. The in vitro methods are also limited to modeling absorption and the interactions that occur. Algorithms to estimate zinc absorption, based on dietary content of zinc absorption modifiers, have been derived from human studies. An algorithm derived from studies of zinc retention from radioactive zinc-labeled test meals underestimates zinc absorption compared to that derived from measurement of true zinc absorption from total diets using isotopic tracer methods. Based on the latter, phytate appears to be the only major inhibitor of zinc absorption from typical diets. Ultimately, population-based studies are needed to determine the impact of dietary factors that modulate zinc absorption on the adequacy of zinc status.

Effects of water renewal estimates on the oyster aquaculture potential of an inshore area

Tidal and wind renewal of water in the coastal zone is important in the transport of natural and anthropogenic particles and solutes. Models of these systems require detailed parameterization of exchange processes. Renewal of seston food supplies for cultured suspension-feeding shellfish is one such application. This study examines the sensitivity of food limitation estimates of an inshore region for shellfish aquaculture to the methods used in calculating the region's water renewal time. The region is the Indian Island oyster culture site in the Richibucto estuary, New Brunswick, Canada, and the methods considered are the volume advection and the local conservative tracer methods. In both cases, water renewal is calculated from field time series measurements of hydrodynamic parameters and outputs of coupled hydrodynamic and advection–dispersion three-dimensional (3D) numerical models. A comparison of oyster food demand and supply is then made to estimate the food limitation risk in the region using field measurements of biological parameters and the renewal times previously estimated. It is found that water renewal by tides is efficient but it can be cancelled altogether by meteorological forcing. Contrary to the conservative tracer method, the tidal prism method proves to be inadequate when estimating water renewal in estuarine tidal channels and was replaced by another volume advection method. The preliminary results obtained using the depletion index estimates indicate that the Indian Island region could sustain a high oyster biomass. These simple calculations also show the importance of water renewal estimate for carrying capacity studies. Hence, the tidal prism method or other volume advection estimates should be used with great caution or be avoided altogether in such studies.

The use of tracers to evaluate the importance of bioturbation in remobilising contaminants in Baltic sediments

Large areas of the bottom sediments of the Baltic Sea are temporarily or permanently anoxic. These sediments are also an important sink for a variety of contaminants. Reoxygenation of bottom waters allows recolonisation by benthic infauna, which may have important implications for the fate of buried contaminants. This study used tracers to experimentally examine the role of bioturbation by benthic infauna in transporting sediment-associated contaminants in the Baltic Sea. Three different tracer methods were used in two experiments, using three key Baltic macrofaunal species: the amphipod crustacean Monoporeia affinis; the Baltic clam Macoma baltica; and the priapulid worm Halicryptus spinulosus. In the first experiment, a reoxygenation–recolonisation scenario was recreated in the laboratory, using hypoxic sediment cores collected in the field, to determine if there was remobilisation of buried 137Cs from the Chernobyl nuclear accident in 1986. The potential for the infauna to bury newly settled surface contamination was also investigated, using a fluorescent particle tracer. In the second experiment, artificially-created radiolabelled tracer layers ( 14C and 51Cr) were used to quantify both upward and downward movements of organic matter and sediment-associated contaminants by bioturbation. In both experiments there were clear visual differences between the sediment effects of the three species. Halicryptus spinulosus buried deepest into the sediment, creating a network of burrows, Monoporeia affinis burrowed actively in the upper few centimeters of the sediment, and Macoma baltica was quite stationary, but appeared to filter- and deposit feed at the sediment surface. Mixing depths in the hypoxic sediment varied from 4.0 ± 3.5 cm for M. baltica to 7.8 ± 2.1 cm for H. spinulosus. Biodiffusion rates ( D b) were similar for all treatments but biotransport rates ( r) were significantly different between treatments, mainly due to a high r value for H. spinulosus. In the experiment with radiolabelled tracer layers, 51Cr was transported more than 14C, and tracer originally at the surface transported more than tracer buried 4 cm below the surface. There was also transport of all tracers in treatments without added macrofauna. The most likely explanation is bioturbation by the meiofauna that were undoubtedly present in both experiments. Bioturbation by macrofauna both buries surface contaminants and remobilises those that are buried, but the effects are small and on a similar scale to transport caused by meiofauna. In addition, 137Cs profiles at the hypoxic site indicated that resuspension and redeposition of sediment by physical processes had occurred, and also showed that contaminants from the last 40 years were still present in the top 5–10 cm of the sediment, well within active mixing depths. At this site, as at many others in the Baltic, physical processes are likely to be far more important than biological processes in the redistribution of contaminants on a decadal timescale.

On diffusion in the β-NiAl phase

Interdiffusion coefficients in the β-NiAl phase over the homogeneity range are determined by the diffusion couple technique in the temperature range of 1000–1200 °C. Intrinsic diffusivities of the species at 1000 °C at different compositions are measured by Kirkendall marker experiments. The variations of the molar volume with composition and partial molar volumes of the species, required for the determination of the diffusion parameters, are calculated using lattice parameter and vacancy concentration. Tracer diffusion coefficients of the species were calculated from the knowledge on intrinsic diffusivities and compared with the data available in the literature, which were measured directly by tracer methods. The influence of the vacancy wind effect is determined on the calculated results.

A global comparison of subtropical underwater formation rates

Subduction-related formation rates for Subtropical Underwater (STUW) are estimated for the North Atlantic and South Indian Oceans and compared with earlier work for the North and South Pacific. Subduction rates are calculated using drifter (1988–1998) and tracer (1987–1995) data. The drifter method involves calculating lateral induction (LI) from the mixed layer depth gradient, and vertical pumping (VP) from Ekman convergence. The tracer method involves calculating pCFC-12 ages on density surfaces to estimate the inverse age gradient. The two methods are independent except for the calculation of the formation area. The tracer and drifter methods agree within the error estimates, except in the North Pacific, and can be used to put bounds on the STUW subduction process: North Atlantic (44–36 m/yr, 2 Sv), North Pacific (26–17 m/yr, 4 Sv), South Pacific (32–33 m/yr, 7 Sv), and South Indian (22–25 m/yr, <1 Sv). In the drifter method, analysis of the terms contributing to subduction of STUW shows, LI is negligible in the North Atlantic and North Pacific, and positive in the South Pacific. In the South Indian Ocean LI is large and negative due to the anomalous poleward location of the STUW. Ekman pumping (EP) is highest in the South Indian Ocean followed by the North Atlantic, consistent with the strength of the wind stress curl. The North Pacific has smaller EP than the South Pacific, even though the wind stress curl is higher in the North. This effect is mainly due to the location of South Pacific STUW closer to the equator than the North Pacific STUW, and more buoyancy forcing in the South Pacific Ocean. The conclusion is that there is considerable variation in thermocline ventilation between ocean gyres.

Mechanistic study on the methane activation over various supported molybdenum carbide catalysts with isotopic tracer methods

The mechanism of methane activation in CH 4 CO 2 reaction over various unsupported and supported Mo 2C catalysts was studied by means of an isotopic tracer technique employing 13CH 4 and CD 4 as tracers. Incorporation of carbide carbons into CO took place in the case of CH 4 CO 2 reaction over unsupported Mo 2C, which was retarded significantly by dispersing Mo 2C onto ZrO 2 support. Methane dissociation step was also retarded significantly over supported Mo 2C catalysts, and the durability of the catalysts was improved by preventing inactive carbon accumulation. By dispersing Mo 2C on Al 2O 3, novel active acidic sites were produced, where CH 4 CD 4 exchange reaction took place even below room temperature through an associative mechanism.

Simultaneous estimation of diffusive Volatile Organic Compound (VOC) fluxes and Non‐Aqueous Phase Liquid (NAPL) saturation in the vadose zone

AbstractSoil‐gas monitoring is a widely used tool to observe the migration of volatile organic compounds (VOCs) at contaminated sites. By combining this technique with natural gradient tracer methods, diffusive contaminant fluxes can be measured in situ, and non–aqueous phase liquid (NAPL) can be detected and roughly quantified. This work describes the new approach and its application at a field site in Denmark with an emplaced NAPL contamination. Soil‐gas probes with a low dead volume were installed at 1‐m depths in the sandy vadose zone, and a small volume of gas containing conservative and partitioning tracers was injected. Soil‐gas samples were withdrawn subsequently during 1 to 4 h and analyzed simultaneously for VOCs and tracers. Tracers detected the NAPL reliably, and the combined data allowed for a close delineation of the source zone. The calculated NAPL saturation deviated by up to a factor of 3 from the analyses of soil cores. Better agreement was found by taking the NAPL composition into consideration, which is, however, generally unknown at the actual field sites. In addition, the tracers were also used to estimate effective diffusion coefficients in situ, which varied by a factor of 2 between various locations. From these data, diffusive contaminant vapor fluxes were quantified without additional laboratory experiments or the use of empirical relationships. The new approach yields a better site investigation with a few additional measurements.

Intelligent Biohybrid Materials for Therapeutic and Imaging Agent Delivery

Many molecular imaging techniques rely on tracer methods to visualize specific physiological processes in cells, animals, and humans. A new family of "smart" delivery systems for biomolecules has opened new opportunities for the molecular imaging field. One class of polymeric carriers reversibly become membrane destabilizing in response to sharp pH changes and were designed for delivering proteins and nucleic acids to intracellular compartments. These carriers could enable the use of imaging agents and intracellular reporters whose site of action made them previously inaccessible. A second class of stimuli-responsive polymer-biomolecule conjugates can be reversibly formed into particles of closely defined sizes. The ability to control when and where the protein or DNA species is in the free versus particle form may allow imaging applications that exploit their differential size and diffusion properties.

Estimation of stream nutrient uptake from nutrient addition experiments

Nutrient uptake in streams is often quantified by determining nutrient uptake length. However, current methods for measuring nutrient uptake length are often impractical, expensive, or demonstrably incorrect. We have developed a new method to estimate ambient nutrient uptake lengths using field experiments involving several levels of nutrient addition. Data analysis involves plotting nutrient addition uptake lengths versus added concentration and extrapolating to the negative ambient concentration. This method is relatively easy, inexpensive, and based on sound theoretical development. It is more accurate than the commonly used method involving a single nutrient addition. The utility of the method is supported by field studies directly comparing our new method with isotopic tracer methods for determining uptake lengths of phosphorus, ammonium, and nitrate. Our method also provides parameters for comparing potential nutrient limitation among streams.

Storm flow flushing in a structured soil changes the composition of dissolved organic matter leached into the subsoil

Dissolved organic matter increases typically in streams draining forested catchments during heavy rainstorms and snowmelt. Tracer methods and model calculations suggest that the storm flow flushing of dissolved organic matter is either due to lateral near-surface flow, i.e. within the organic forest floor, or preferential flow (funnelling) through the mineral soil. Both pathways should deliver forest floor-derived dissolved organic matter to streams that is hardly changed because of little to no interaction with mineral soil material and microorganisms. Here, we investigated the effect of rain storm induced vertical flushing through the mineral soil on the composition of dissolved organic matter in a structured Rendzic Leptosols under 90-year-old European beech ( Fagus sylvatica L.). During two rainstorm periods in autumn 1998 with elevated transport of organic C, N, P and S from the forest floor into the subsoil, we sampled dissolved organic matter in forest floor leachates (sampled by zero-tension plate lysimeters), subsoil solutions (sampled by suction cups at 90 cm depth) and subsoil seepage (sampled by zero-tension plate lysimeters at 90 cm depth). The chemical composition of dissolved organic matter was characterised by fractionation with XAD-8 macroreticular resin, wet-chemical analyses of carbohydrates and lignin-derived phenols, and determination of the δ 13C. During both rainstorm periods, all tested chemical features of dissolved organic matter in forest floor leachate and subsoil seepage matched each other greatly. In contrast, dissolved organic matter in soil solution contained smaller portions of XAD-8-adsorbable organic C, less lignin-derived phenols, more carbohydrates and showed smaller δ 13C values than that in forest floor leachates and subsoil seepage. These results suggest a rather direct transfer of organic solutes from the forest floor into the subsoil and probably further to ground and surface waters during heavy rainstorms. Dissolved organic matter leaving the soil in heavy rainstorms by rapid water flow through macropores is likely less biodegradable, more UV-digestible and more reactive towards metals and organic pollutants than that released from soil at low rainfall intensity by matric flow.

Molecular imaging: what can be used today

Biochemical cellular targets and more general metabolic processes in cancer cells can be visualised. Extensive data are available on molecular imaging in preclinical models. However, innovative tracers move slowly to the clinic. This review provides information on the currently available methods of metabolic imaging, especially using PET in humans. The uptake mechanisms of tracer methods and a brief discussion of the more ‘molecular’ targeted methods are presented. The main focus is on the different classes of tracers and their application in various types of cancer within each class of tracers, based on the current literature and our own experience. Studies with [18F]FDG (energy metabolism), radiolabelled amino acids (protein metabolism), [18F]FLT (DNA metabolism), [11C]choline (cell membrane metabolism) as general metabolic tracer methods and [18F]DOPA (biogenic amine metabolism) as a more specific tracer method are discussed. As an example, molecular imaging methods that target the HER2 receptor and somatostatin receptor are described.

2641 爪チャックの回転に起因するCNC旋盤加工空間内の空気流挙動の数値解析(G13 新加工技術,G13 生産加工・工作機械)

In order to solve some problems relating to airflow caused by rotating chuck of a CNC lathe or turning center, the airflow in a closed space assumed a machining space is investigated by the MAC (Maker-and-Cell) method. An analytical model and calculated grids are a three-dimensional space assumed a machining space and the staggered grids respectively. The analytical results have good accordance with characteristic airflow patterns observed by means of the tuft and tracer methods; (1) A radial airflow blowing from the rotating chuck strikes the panel near the headstock side, and then goes in the direction of tailstock through the surface of panel. (2) An entrained-flow exists around the rotating chuck. (3) The separation of airflow from the panel is observed on the left, right, upper and bottom panels.

Comparative evaluation of hight tracer, Chandra tracer, intraoral tracer, functiograph and checkbite: A clinical study

PURPOSE: Centric and eccentric relations of mandible can be recorded through check bites, graphic recordings, functional recordings and cephalometrics. These records are then transferred to a semi-adjustable articulator so that it can be set to simulate the human system. This study is an attempt to compare the relative accuracy of the checkbite and graphic recordings using cephalometrics as a standard. AIMS: • To compare the efficiency of hight tracer, Chandra tracer, Conventional intraoral tracer, Functiograph and Checkbite in determining centric relation. • To compare the efficiency of hight tracer, Chandra tracer, Conventional intraoral tracer, Functiograph and Checkbite in determining horizontal condylar guidance angle on Hanau H2 articulator with the aid of both centric and eccentric records. • To compare the horizontal angle values thus obtained on the Hanau H2 articulator with horizontal angle values in cephalometric tracings. MATERIALS AND METHODS: Hight tracer, Chandra tracer, Conventional intraoral tracer, Functiograph and Checkbite were used on 10 edentulous subjects to obtain centric and protrusive records. Lateral cephalograms were made at both centric and protrusive positions with each method and the horizontal condylar values thus obtained were compared with those obtained on Hanau H2 articulator. RESULTS: • There was no statistical difference between the cephalometric and articulator values in all the five experimental methods. • There was no significant difference between Hight tracer, Chandra tracer, Intraoral tracer, Functiograph and Checkbite methods. • Ranking the experimental methods in the order of efficiency: the first was the Intraoral tracer, second being Functiograph followed by Chandra tracer, Checkbite and Hight tracer. • Checkbite alone can be used to set the horizontal angles on the articulator in edentulous subjects, clinically. • Tracings can be used as a verificatory method. • Centric relation position was found to be the same in a subject with all the experimental methods. • Each experimental method can influence the condylar path differently in the eccentric position. CONCLUSIONS: The articulator value of horizontal condylar angle was higher than cephalometric value in majority of the subjects in all the five experimental methods.

PHOSPHORUS CYCLING IN TERRESTRIAL ECOSYSTEMS AND ITS CONTROLLING FACTORS

Phosphorus (P) is a key element of all life and the limiting nutrient in many ecosystems of the world. P biogeochemistry partly controls ecosystem structure and function. Over the past couple of decades, the importance of P biogeochemistry in controlling terrestrial ecosystem processes has received increasing attention . Advances in P cycling in terrestrial ecosystems were reviewed in this paper. Characteristics of P cycling in ecosystem were attributed to factors such as the source of P, the chemical form, traits in soils and the complexity of its controlling factors. P in terrestrial ecosystems is derived mainly from weathering of apatite, and biological and chemical processes, such as microbial absorption, precipitation and adsorption by Fe and Al oxides and CaCO3, easily immobilize P in soil. Transformations of P between different chemical forms in the e-cosystem, especially in the soil, and its controlling factors were discussed in detail. P cycling in terrestrial e-cosystems is mainly intra-ecosystem cycling which is controlled mainly by the genotype of plant and soil properties , especially pH and ion concentration. The relative importance of different controlling factors differs among ecosystems and across temporal and spatial scales. Also, methods for studying P cycling in terrestrial ecosystems were reviewed. Pot experiments, fertilization trials and sequential extraction procedures were commonly used to test for the bioavailability of different forms of soil P; however, in situ field experiments that used resin bags, litter bags, new isotope tracer methods using 32P and 33P, and NMR spectroscopy to study P dynamics and the chemical structure of soil P were more useful for understanding P cycling and plant availability. Additionally , the significance of P cycling in arid regions was analyzed. P cycling in arid regions, where vegetation is sparse and soil is infertile, are very different from humid regions, and ecosystems there are more easily limited by P. Finally, the trends and hotspots of P cycling in terrestrial ecosystems are summarized for different temporal and spatial scales, different study areas and contents.

Experimental evidence of fast groundwater responses in a hillslope/floodplain area in the Black Forest Mountains, Germany

AbstractAnalysis of water flow pathways from hillslopes to streams is essential for the optimal protection of water resources as well as for ecohydrological studies. This study addresses runoff generation processes at a hillslope and near‐stream shallow groundwater system in the Black Forest Mountains, southwestern Germany. The changing spatial and temporal flow patterns during differing hydrological situations were examined using a combined hydraulic and hydrochemical approach. Groundwater levels at 10 wells, discharge at a near‐stream saturated area, and several natural tracers (deuterium, dissolved silica, and major anions and cations) were observed at different locations during high and low flows. The importance of the groundwater component during flood formation was clearly demonstrated: its contribution was about 80% during a double peak flood event at the saturated area. In addition, a rapid change of the shallow groundwater levels was observed along two transects of groundwater wells in the floodplain. This led to an enhanced groundwater discharge into the saturated area located at the end of one study transect. The amount of groundwater additionally activated during the event was about 30% of total discharge recorded at the outlet of the saturated area. Two alternative hypotheses are discussed to explain this phenomenon: the establishment of locally confined conditions and the development of a pressure wave (hypothesis A), or the significant change of the three‐dimensional groundwater flow lines that caused a large increase of the groundwater catchment at the saturated area during the investigated event (hypothesis B). Even if the exact flow paths and mechanisms could not be clearly identified, the importance of rapid responding hillslope groundwater was undoubtedly demonstrated by a combination of tracer and hydrometric methods. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Route of Tracer Administration Does Not Affect Ileal Endogenous Nitrogen Recovery Measured with the 15N-Isotope Dilution Technique in Pigs Fed Rapidly Digestible Diets

The (15)N-isotope dilution technique ((15)N-IDT), with either pulse-dose oral administration or continuous i.v. administration of [(15)N]-l-leucine (carotid artery), both at 5 mg/(kg body weight . d), was used to measure ileal (postvalve T-cecum cannula) endogenous nitrogen recovery (ENR) in pigs (9 +/- 0.6 kg). Diets were cornstarch, enzyme-hydrolyzed casein with no (control) or high (4%) content of quebracho extract (Schinopsis spp.) rich in condensed tannins. Blood was sampled from a catheter in the external jugular vein. Mean plasma (15)N-enrichment at d 8-10 was higher (P = 0.0009) after i.v. than after oral administration [0.0356 vs. 0.0379 atom% excess (APE)]. Plasma (15)N-enrichment for i.v. infused pigs was 0.01117 APE higher (P < 0.0001) and for orally dosed pigs 0.0081 APE lower (P < 0.0001) at 11 h postprandial compared with 1 h postprandial. Apparent ileal N digestibility was higher (P < 0.0001) for the control (85.5%) than for the quebracho diet (69.5%). ENR was calculated from the ratio of (15)N-enrichment of plasma and digesta. The ENR for the quebracho diet was approximately 300% higher than for the control diet (6.03 vs. 1.94 g/kg dry matter intake, P < 0.001). The real N digestibility (92.2 +/- 0.4%) was equal for both diets (P = 0.1030) and both tracer methods (P = 0.9730). We concluded that oral administration of [(15)N]leucine provides reasonable estimates of ENR in pigs fed semipurified diets with high or low content of tannins; however, one must be careful in extrapolating this conclusion to studies with other protein sources or feeding frequencies.

Endogenous Glucose Production in Type 2 Diabetes: Basal and Postprandial. Role of Diurnal Rhythms

Glycemia in type 2 diabetes is characterized by a nonsteady but stable diurnal cycle. This leads to morning fasting hyperglycemia. It arises from an underlying circadian pattern in endogenous glucose production because the metabolic clearance rate of glucose is decreased but constant. Therefore, it is important to use appropriate nonsteady tracer methods to measure this rate even under basal conditions. Postprandially, in diabetes, the endogenous glucose production continues to decrease, with only minor deviations from the slope of the basal curve. This suggests a decoupling of endogenous glucose production from the regulatory factors (insulin, glucose) that prevail under normal circumstances. As the duration of diabetes increases, metabolic clearance of glucose continues to deteriorate. This may be partially compensated by a decrease in glucose production. This rate remains, however, inappropriate because its impact on glycemia does not decline.

Mercury speciation and microbial transformations in mine wastes, stream sediments, and surface waters at the Almadén Mining District, Spain.

Speciation of Hg and conversion to methyl-Hg were evaluated in mine wastes, sediments, and water collected from the Almadén District, Spain, the world's largest Hg producing region. Our data for methyl-Hg, a neurotoxin hazardous to humans, are the first reported for sediment and water from the Almadén area. Concentrations of Hg and methyl-Hg in mine waste, sediment, and water from Almadén are among the highestfound at Hg mines worldwide. Mine wastes from Almadén contain highly elevated Hg concentrations, ranging from 160 to 34,000 microg/g, and methyl-Hg varies from <0.20 to 3100 ng/g. Isotopic tracer methods indicate that mine wastes at one site (Almadenejos) exhibit unusually high rates of Hg-methylation, which correspond with mine wastes containing the highest methyl-Hg concentrations. Streamwater collected near the Almadén mine is also contaminated, containing Hg as high as 13,000 ng/L and methyl-Hg as high as 30 ng/L; corresponding stream sediments contain Hg concentrations as high as 2300 microg/g and methyl-Hg concentrations as high as 82 ng/g. Several streamwaters contain Hg concentrations in excess of the 1000 ng/L World Health Organization (WHO) drinking water standard. Methyl-Hg formation and degradation was rapid in mines wastes and stream sediments demonstrating the dynamic nature of Hg cycling. These data indicate substantial downstream transport of Hg from the Almadén mine and significant conversion to methyl-Hg in the surface environment.