Multinational comparison study of aircraft pilot healthcare avoidance behaviour.

BACKGROUND: US and Canadian pilots are required to meet medical standards to secure their active flying status, but a subgroup exhibit healthcare avoidance behaviour due to fear of loss of that status. This phenomenon has the potential to impact pilot health, aeromedical screening and aviation safety. No international comparison study of pilot healthcare avoidance currently exists between US and Canadian pilots. AIMS: To compare the rate and subtypes of healthcare avoidance behaviour secondary to fear for loss of flying status between US and Canadian pilots. METHODS: A comparison analysis of data collected during two independent, non-probabilistic, cross-sectional internet surveys including any individual certified to perform flying duties in the USA (US survey) or Canada (Canadian survey). RESULTS: There were 4320 US pilots and 1415 Canadian pilots who completed informed consent and 3765 US pilots and 1405 Canadian pilots were included in the results. There were 56% of US pilots who reported a history of healthcare avoidance behaviour compared to 55% of Canadian pilots (P = 0.578). A multivariable logistic regression that included age, pilot type and gender showed that US pilots were slightly more likely than Canadian pilots to report this behaviour (odds ratio 1.22, 95% confidence interval 1.06-1.4). CONCLUSIONS: Healthcare avoidance behaviour due to fear of loss of flying status has a relatively high prevalence in both US and Canadian pilot populations.

Soil nitrogen dynamics in a river floodplain mosaic.

In their natural state, river floodplains are heterogeneous and dynamic ecosystems that may retain and remove large quantities of nitrogen from surface waters. We compared the soil nitrogen dynamics in different types of habitat patches in a restored and a channelized section of a Thur River floodplain (northeast Switzerland). Our objective was to relate the spatiotemporal variability of selected nitrogen pools (ammonium, nitrate, microbial nitrogen), nitrogen transformations (mineralization, nitrification, denitrification), and gaseous nitrogen emission (NO) to soil properties and hydrological processes. Our study showed that soil water content and carbon availability, which depend on sedimentation and inundation dynamics, were the key factors controlling nitrogen pools and processes. High nitrogen turnover rates were measured on gravel bars, characterized by both frequent inundation and high sediment deposition rates, as well as in low-lying alluvial forest patches with a fine-textured, nutrient-rich soil where anaerobic microsites probably facilitated coupled nitrification-denitrification. In contrast, soils of the embankment in the channelized section had comparatively small inorganic nitrogen pools and low transformation rates, particularly those related to nitrate production. Environmental heterogeneity, characteristic of the restored section, favors nitrogen removal by creating sites of high sedimentation and denitrification. Of concern, however, are the locally high NO efflux and the possibility that nitrate could leach from nitrification hotspots.

Analysis of carbon and nitrogen dynamics in riparian soils: model validation and sensitivity to environmental controls.

The Riparian Soil Model (RSM) of Brovelli et al. (2012) was applied to study soil nutrient turnover in a revitalized section of the Thur River, North-East Switzerland. In the present work, the model was calibrated on field experimental data, and satisfactorily reproduced soil respiration, organic matter stocks and inorganic nitrogen fluxes. Calibrated rates were in good agreement with the ranges reported in the literature. The main discrepancies between model and observations were for dissolved organic carbon. The sensitivity of the model to environmental factors was also analyzed. Soil temperature was the most influential factor at daily and seasonal scales while effects of soil moisture were weak overall. The ecosystem sensitivity to temperature changes was quantified using the Q10 index. The seasonal behavior observed was related to the influence of other forcing factors and to the different state (density and activity) of the microbial biomass pool during the year. Environmental factors influencing microbial decomposition, such as the C:N ratio and litter input rate, showed intermediate sensitivity. Since these parameters are tightly linked to the vegetation type, the analysis highlighted the effect of the aboveground ecosystem on soil functioning.

Metal solubility and speciation in the rhizosphere of Lupinus albus cluster roots.

The objective of this study was to investigate the influence of root exudation of organic acid anions on the speciation of major and trace metal cations in the rhizosphere of Lupinus albus cluster roots. Plants were grown in rhizoboxes containing repacked weakly acidic loam. Bulk soil solutions and, during the lifetime of cluster roots, rhizosphere solutions were collected using micro suction cups. During organic acid anion exudation bursts, metals in the rhizosphere of cluster roots were strongly mobilized. The concentrations of dissolved organic carbon derived from soil organic matter increased parallel to organic acid anions. Speciation calculations revealed that, during exudation, Al, Ca, Mn, and Zn in the cluster root rhizosphere were mainly bound with citrate, while Cu and Pb were always strongly bound to soil-derived dissolved organic matter. Our results indicate that cluster root exudation led on one hand to direct mobilization and complexation of metals like Al, Fe, and Zn by citrate and on the other hand to the mobilization of soil organic matter which complexes and solubilizes Cu and Pb.

Sorption of trace metals by standard and micro suction cups in the absence and presence of dissolved organic carbon.

Both the bioavailability of a trace metal (TM) in a soil and the risk of leaching to the ground water are linked to the metals concentration in the soil solution. Sampling soil solution by tension lysimetry with suction cups is a simple and established technique that is increasingly used for monitoring dissolved TM in soils. Of major concern, however, is the sorption of TM by the walls of the samplers. Metal sorption by different materials used in suction cups can vary widely, depending also on the chemistry of the soil solution. We compared the sorption of Cu, Zn, Cd, and Pb by different standard-size and micro suction cups in the laboratory at two pH values (4.5 and 7.5 or 8.0) in absence and presence of dissolved organic carbon (DOC). In addition, we investigated the sorption of DOC from different origins by the cup materials. At both pH values, the weakest sorption of all four TMs was exhibited by standard-size suction cups based on nylon membranes and by hollow fibers made from polyvinyl alcohol (PVA). At alkaline pH, borosilicate glass, ceramic materials, and polytetrafluorethylene (PTFE) mixed with silicate were characterized by generally strong sorption of all investigated TMs. In addition, Cu and Pb were strongly sorbed at low pH by PTFE-silicate and a ceramic material used for the construction of standard-size suction cups. On the other hand, sorption of Cu, Zn, and Cd by ceramic capillaries produced from pure aluminum oxide was negligible at low pH. Micro suction cups made of an unknown polymerous tube sorbed Cu strongly, but were well suited to monitor Zn, Cd, and Pb at low pH, and, in the presence of DOC, also at high pH. Major cations (Na+, Mg2+, K+, Ca2+) and anions (Cl-, NO3-, SO4(2-)) were not or very weakly sorbed by all cup materials, except for Mg2+, K+, and Ca2+ by borosilicate glass at pH 7.5. Trace metal sorption by suction cups was generally greatly reduced in the presence of DOC, especially at alkaline pH. The sorption of DOC itself depended on its source. Dissolved organic carbon from leaf litter extracts with a probably large hydrophobic fraction was sorbed more strongly than mainly hydrophilic DOC from a mineral soil solution.

Critical examination of trace element enrichments and depletions in soils: As, Cr, Cu, Ni, Pb, and Zn in Swiss forest soils.

The aim of this study was to obtain an overview of trace element concentrations in Swiss forest soils and to critically assess the measured values with respect to anthropogenic input vs. lithogenic background. Twenty-three sites were selected which represent a broad range of natural forest sites, bedrock material and soil types of Switzerland. At each site, samples were collected from all genetic soil horizons down to a C or B/C horizon. Total concentrations of As, Cr, Cu, Ni, Pb, and Zn in all samples were determined by X-ray fluorescence spectrometry. There were distinct differences in the geological background values estimated from the concentrations measured in the samples from the lowest soil horizon. Background concentrations for Cr and Ni were lowest in granite and gneiss, whereas Pb and Zn were highest in limestone and marl. Enrichment or depletion of the trace elements was assessed using Zr as reference element. Within the same profile, the six trace elements showed completely different enrichment/depletion patterns with depth. The various natural processes and anthropogenic inputs that can lead to these patterns are critically discussed. Based on this critical assessment, pollution of the investigated forest soils was found to be most severe for Pb and Zn and to a somewhat lesser extent for As and Cu, whereas anthropogenic input of Cr and Ni seems to be less important. The data suggest that a critical evaluation of enrichment factors is a better tool to assess soil pollution with trace elements than the use of maximum allowable concentrations (MAC) for topsoil samples. The enrichment factors calculated as described here consider the effects of geological variation on metal abundances whereas the MAC does not. In order to obtain an estimate of soil solution concentrations, water extracts of the samples collected from a subset of 10 soil profiles were analyzed for the same trace elements. Solubility of all elements generally decreased with soil depth. An exception was Cr, Cu, and Ni solubility in the humus layer, which was lower than in the underlying mineral horizon. For all elements, solubility was higher for the collective of soil samples depleted in this element when compared to the samples, in which the element was enriched.

Immediate provisional and long-term anterior prosthodontics: a comprehensive approach.

The success of any anterior prosthodontic restoration depends on many factors. Considering those multiple influences during treatment planning can profoundly affect the long-term success of such cases. Comprehensive dental care involves evaluating all available restoration options for treating any given patient's condition. The dentist is obligated to present all of these options to the patient without bias. The following case reports provide a perspective from which decision-making occurs before treatment planning is accomplished.

Equilibrium ion exchange method: methodology at low ionic strength and copper(II) complexation by dissolved organic matter in a leaf litter extract.

The equilibrium ion exchange method (EIM) is a powerful tool for the investigation of metal cation complexation by dissolved organic matter (DOM) in natural systems. Tests with different ion exchange resins demonstrated that under low ionic strength conditions (0.01 mol/kg) and in the presence of DOM, equilibration times of at least 24 h are required for experiments with Cu(II). The classical approach to the EIM was modified by using nonlinear reference adsorption isotherms in order to expand the method to a broader range of experimental conditions. For Cu(II) at low ionic strength (0.01 mol/kg), the reference isotherms between pH 4 and 6 were identical and were mathematically modeled in terms of Langmuir adsorption parameters. The EIM using nonlinear reference isotherms was validated between pH 4 and 6 by the correct determination of the stability constants for the complexes CuOxalate and Cu(Oxalate)(2). Then the method was used to quantitatively characterize the Cu(II) complexation behavior of DOM in an aqueous chestnut leaf litter extract between pH 4 and 6. In contrast to the classical approach to the EIM, data were analyzed by using plots [Cu](bound)/[Cu](free)vs. [Cu](bound). This allowed the determination of both, conditional stability constants and metal binding capacities for two different binding site classes. The logarithmic values of the stability constants were about 8 for the strong binding sites and 5.5-6 for the weak binding sites. The total Cu(II) binding capacity increased from 0.22 mol/(kg C) at pH 4 to 2.85 mol/(kg C) at pH 6.