The effect of magnetic resonance imaging on mercury release from dental amalgam at 3T and 7T.

OBJECTIVES: To measure mercury release from standardised hydroxyapatite/amalgam constructs during MRI scanning and investigate the impact of static field strength and radiofrequency (RF) power on mercury release. METHODS: Amalgam was placed into 140 hydroxyapatite disks and matured for 14-days in artificial saliva. The solution was replaced, and samples split into five groups of 28 immediately prior to MRI. One group had no exposure, and the remainder were exposed to either a 3T or 7T MRI scanner, each at high and low RF power. Mercury concentration was measured by inductively coupled plasma mass spectrometry. Groups were compared using one-way ANOVA, and two-way ANOVA for main effects/ interaction of field strength/ RF power. RESULTS: Mercury concentration was increased in the 7T groups (high/ low: 15.43/ 11.33 ng mL-1) and 3T high group (3.59) compared to control (2.44). MRI field strength significantly increased mercury release (p < .001) as did RF power (p = .030). At 3T, mercury release was 20.3 times lower than during maturation of dental amalgam, and for the average person an estimated 1.50 ng kg-1 of mercury might be released during one 3T investigation; this is substantially lower than the tolerable weekly intake of 4,000 ng kg-1. CONCLUSION: Mercury release from amalgam shows a measurable increase following MRI, and the magnitude changes with magnetic field strength and RF power. The amount of mercury released is small compared to release during amalgam maturation. Amalgam mercury release during MRI is unlikely to be clinically meaningful and highly likely to remain below safe levels.

Effects of chronic exposure to haloperidol, olanzapine or lithium on SV2A and NLGN synaptic puncta in the rat frontal cortex.

Positron emission tomography studies using the synaptic vesicle glycoprotein 2A (SV2A) radioligand [11C]-UCB-J provide in vivo evidence for synaptic dysfunction and/or loss in the cingulate and frontal cortex of patients with schizophrenia. In exploring potential confounding effects of antipsychotic medication, we previously demonstrated that chronic (28-day) exposure to clinically relevant doses of haloperidol does not affect [3H]-UCB-J radioligand binding in the cingulate and frontal cortex of male rats. Furthermore, neither chronic haloperidol nor olanzapine exposure had any effect on SV2A protein levels in these brain regions. These data do not exclude the possibility, however, that more subtle changes in SV2A may occur at pre-synaptic terminals, or the post-synaptic density, following chronic antipsychotic drug exposure. Moreover, relatively little is known about the potential effects of psychotropic drugs other than antipsychotics on SV2A. To address these questions directly, we herein used immunostaining and confocal microscopy to explore the effect of chronic (28-day) exposure to clinically relevant doses of haloperidol, olanzapine or the mood stabilizer lithium on presynaptic SV2A, postsynaptic Neuroligin (NLGN) puncta and their overlap as a measure of total synaptic density in the rat prefrontal and anterior cingulate cortex. We found that, under the conditions tested here, exposure to antipsychotics had no effect on SV2A, NLGN, or overall synaptic puncta count. In contrast, chronic lithium exposure significantly increased NLGN puncta density relative to vehicle, with no effect on either SV2A or total synaptic puncta. Future studies are required to understand the functional consequences of these changes.

At the world's edge: Reconstructing diet and geographic origins in medieval Iceland using isotope and trace element analyses.

OBJECTIVES: A multi-isotope study was conducted on individuals buried at Skriðuklaustur monastery (AD 1493-1554) to investigate their geographic origins and dietary composition. Comparative material from individuals excavated from Skeljastaðir, an inland farm site was also analyzed. MATERIALS AND METHODS: Bone collagen was extracted from 50 humans (Skriðuklaustur and Skeljastaðir) and 25 animals (Skriðuklaustur) and analyzed for δ13 C, δ15 N, and δ34 S. Dental enamel samples from 31 individuals (Skriðuklaustur) were also analyzed for 87 Sr/86 Sr, δ18 O, δ13 C, and trace elements (Pb, Sr, Zn, Ba). RESULTS: The mean value determined from individuals from Skriðuklaustur (n = 36) was δ13 C = -18.7 ± 0.8‰, δ15 N = 12.8 ± 1.1‰, and δ34 S = 9.0 ± 1.6‰, whereas at Skeljastaðir (n = 14), it was δ13 C = -20.5 ± 0.8‰, δ15 N = 7.8 ± 0.9‰, and δ34 S = 9.4 ± 1.6‰. At Skriðuklaustur, human dental enamel samples (n = 31) provided a 87 Sr/86 Sr range of 0.7060-0.7088, δ18 Ophosphate from 13.9 to 16.1‰ and δ13 Ccarbonate from -16.6 to -12.9‰. Inferred drinking water (δ18 Odw ) values range from -12.3 to -8.9‰. Sr concentrations range from 25.8 to 156.7 ppm, Ba from 0.11 to 0.81 ppm, Zn from 43.8 to 145.8 ppm, and Pb from 0.13 to 9.40 ppm. DISCUSSION: A combination of results indicates that the people from Skriðuklaustur were born in Iceland, but some lived inland during childhood while others lived closer to the coast. Since Skriðuklaustur was a hospital, these individuals may have sought medical treatment at the monastery. The δ13 C and δ15 N values determined from bone collagen indicate that the people residing at Skriðuklaustur consumed a diet high in marine protein, while those residing at Skeljastaðir exhibit values more consistent with terrestrial resources.

Mountain glaciation drives rapid oxidation of rock-bound organic carbon.

Over millions of years, the oxidation of organic carbon contained within sedimentary rocks is one of the main sources of carbon dioxide to the atmosphere, yet the controls on this emission remain poorly constrained. We use rhenium to track the oxidation of rock-bound organic carbon in the mountain watersheds of New Zealand, where high rates of physical erosion expose rocks to chemical weathering. Oxidative weathering fluxes are two to three times higher in watersheds dominated by valley glaciers and exposed to frost shattering processes, compared to those with less glacial cover; a feature that we also observe in mountain watersheds globally. Consequently, we show that mountain glaciation can result in an atmospheric carbon dioxide source during weathering and erosion, as fresh minerals are exposed for weathering in an environment with high oxygen availability. This provides a counter mechanism against global cooling over geological time scales.

Highly saline fluids from a subducting slab as the source for fluid-rich diamonds.

The infiltration of fluids into continental lithospheric mantle is a key mechanism for controlling abrupt changes in the chemical and physical properties of the lithospheric root, as well as diamond formation, yet the origin and composition of the fluids involved are still poorly constrained. Such fluids are trapped within diamonds when they form and so diamonds provide a unique means of directly characterizing the fluids that percolate through the deep continental lithospheric mantle. Here we show a clear chemical evolutionary trend, identifying saline fluids as parental to silicic and carbonatitic deep mantle melts, in diamonds from the Northwest Territories, Canada. Fluid-rock interaction along with in situ melting cause compositional transitions, as the saline fluids traverse mixed peridotite-eclogite lithosphere. Moreover, the chemistry of the parental saline fluids--especially their strontium isotopic compositions--and the timing of host diamond formation suggest that a subducting Mesozoic plate under western North America is the source of the fluids. Our results imply a strong association between subduction, mantle metasomatism and fluid-rich diamond formation, emphasizing the importance of subduction-derived fluids in affecting the composition of the deep lithospheric mantle.

Grain size partitioning of platinum-group elements in road-deposited sediments: implications for anthropogenic flux estimates from autocatalysts.

Twelve road-deposited sediment samples were analyzed for platinum-group elements (PGEs) and Pb in the <63 microm fraction of an urban watershed in Hawaii. Three samples were further fractionated into five size classes, from 63-125 microm to 1000-2000 microm, and these were analyzed for PGEs and Pb. Concentrations in the <63 microm fraction reached 174 microg/kg (Pt), 101 microg/kg (Pd), 16 microg/kg (Rh), and 1.3 microg/kg (Ir). Enrichment ratios followed the sequence Rh>Pt=Pd>Ir. Iridium was geogenic in origin, while the remaining PGEs indicated significant anthropogenic contamination. Palladium, Pt and Rh concentrations and enrichment signals were consistent with PGE bivariate ratios and PGE partitioning in three-way catalysts. Size partitioning indicated that the <63 microm fraction had the lowest PGE concentrations and mass loading percentages. These data suggest that autocatalyst PGE flux estimates into the environment will be significantly underestimated if only a fine grain size fraction is analyzed.