Biomedical subjects

H Wanner

Publications and source records attributed to H Wanner.

5 recordsLinked to original sources

PubMed2001

An integrated sorption-diffusion model for the calculation of consistent distribution and diffusion coefficients in compacted bentonite.

A thermodynamic sorption model and a diffusion model based on electric double layer (EDL) theory are integrated to yield a surface chemical model that treats porewater chemistry, surface reactions, and the influence of charged pore walls on diffusing ions in a consistent fashion. The relative contribution of Stern and diffuse layer to the compensation of the permanent surface charge represents a key parameter; it is optimized for the diffusion of Cs in Kunipia-F bentonite, at a dry density of 400 kg/m3. The model is then directly used to predict apparent diffusivities (Da) of Cs, Sr, Cl-, I- and TcO4- and corresponding distribution coefficients (Kd) of Cs and Sr in different bentonites as a function of dry density, without any further adjustment of surface chemical and EDL parameters. Effective diffusivities (De) for Cs, HTO, and TcO4- are also calculated. All calculated values (Da, De, Kd) are fully consistent with each other. A comparison with published, measured data shows that the present model allows a good prediction and consistent explanation of (i) apparent and effective diffusivities for cations, anions, and neutral species in compacted bentonite, and of (ii) Kd values in batch and compacted systems.

Adsorption↗

PubMed1996

A thermodynamic surface model for caesium sorption on bentonite.

Caesium sorption on Wyoming bentonite MX-80 has been studied in solutions of NaCl, KCl, MgCl(2), CaCl(2), NaNO(3) and Ca (NO(3))(2) of concentrations varying between 0.025 and 1 mol/L, as well as in a weakly saline (I=0.004 ml/L) and a strongly saline (I=0.46 mol/L) natural groundwater. These experiments have been used to derive a thermodynamic model for the interaction of caesium with the bentonite surface in accordance with a surface chemical model, including acid/base reactions developed recently for montmorillonite. The sorption behaviour of caesium on bentonite can be described, within the experimental and model uncertainties, in terms of a one-site ion exchange model. The ion exchange constant obtained for the reaction NaX+Cs(+) left arrow over right arrow CsX+Na(+) (where X represents the ion exchange sites on montmorillonite) is log(10) K(0)(ex)=1.6. Impurities in the bentonite, influencing the concentrations of competing cations, such as Na(+), K(+), Mg(2+) and Ca(2+), have a crucial impact on the sorption of caesium. This impact can be adequately quantified with the present model. The model predictions compare well with sorption data published in the open literature on both Wyoming bentonite MX-80 and other types of bentonite. Distribution coefficients from the literature obtained from both batch and diffusion experiments and varying over four orders of magnitude are reproduced and explained successfully by the model.

Journal Article↗

PubMed1996

Deposition of nitrogen-containing compounds to an extensively managed grassland in central Switzerland.

During four intensive observation periods in 1992 and 1993, dry deposition of nitrogen dioxide (NO(2)) and ammonia (NH(3)), and wet deposition of nitrogen (N) were determined. The measurements were carried out in a small, extensively managed litter meadow surrounded by intensively managed agricultural land. Dry deposition of NH(3) was estimated by the gradient method, whereas eddy correlation was used for NO(2). Rates of dry deposition of total nitrate (= nitric acid (HNO(3)) + nitrate (NO(3)(-))), total nitrite (= nitrous acid (HONO) + nitrite (NO(2)(-))) and aerosol-bound ammonium (NH(4)(+)) were estimated using deposition velocities from the literature and measured concentrations. Both wet N deposition and the vertical NH(3) gradient were measured on a weekly basis during one year. Dry deposition was between 15 and 25 kg N ha(-1) y(-1), and net wet deposition was about 9.0 kg N ha(-1) y(-1). Daily average NO(2) deposition velocity varied from 0.11 to 0.24 cm s(-1). Deposition velocity of NH(3), was between 0.13 and 1.4 cm s(-1), and a compensation point between 3 and 6 ppbV NH(3) (ppb = 10(-9)) was found. Between 60 and 70% of dry deposition originated from NH(3) emitted by farms in the neighbourhood. It is concluded that total N deposition is exceeding the critical load for litter meadows, is highly correlated to local NH(3) emissions, and that NH(3) is of utmost importance with respect to possible strategies to reduce N deposition in rural regions.

Journal Article↗

PubMed1985

[Effect of meteorologic and air hygiene factors on acute respiratory tract diseases in children--based on the example of the Biel region].

In the area of a Swiss town (Biel) and its surroundings, cases of various acute respiratory illnesses among children were recorded and correlated with measured parameters of weather and air pollution (sulfur dioxide, dust) during a period of 17 months. An increase in cases was noted during the fall and winter months, involving low temperatures, high humidity and weather conditions with northerly synoptic winds. Also, correlation of the cases to SO2 deposition values revealed a significant connection that may possibly be simulated by identical seasonal changes. No significant connection could be found between concentrations of SO2 or dust values and frequency of illness.

Air Pollutants↗

PubMed1976

[A follow-up of x-ray-treated tuberous hemangiomas after 15-20 years (author.s transl)].

The treatment of hemangiomas with X-rays has been sharply criticized because of their tendency to involute spontaneously. It has been the aim of this catamnestic study to re-examine for X-ray injury those patients, whose hemangiomas were irradiated 15-20 years ago. The findings indicate that signs of roentgenoderma can appear already with 800 r and increase rapidly over 1,500 r. The observed irreversible damages, however, were mostly not grave, but admonish a certain amount of restraint. An assessment of the effectiveness of low X-ray doses still requires verification considering a faster spontaneous involution.

Dose-Response Relationship, Radiation↗