Exposure of silver-nanoparticles and silver-ions to lung cells in vitro at the air-liquid interface

BACKGROUND: Due to its antibacterial properties, silver (Ag) has been used in more consumer products than any other nanomaterial so far. Despite the promising advantages posed by using Ag-nanoparticles (NPs), their interaction with mammalian systems is currently not fully understood. An exposure route via inhalation is of primary concern for humans in an occupational setting. Aim of this study was therefore to investigate the potential adverse effects of aerosolised Ag-NPs using a human epithelial airway barrier model composed of A549, monocyte derived macrophage and dendritic cells cultured in vitro at the air-liquid interface. Cell cultures were exposed to 20 nm citrate-coated Ag-NPs with a deposition of 30 and 278 ng/cm2 respectively and incubated for 4 h and 24 h. To elucidate whether any effects of Ag-NPs are due to ionic effects, Ag-Nitrate (AgNO3) solutions were aerosolised at the same molecular mass concentrations. RESULTS: Agglomerates of Ag-NPs were detected at 24 h post exposure in vesicular structures inside cells but the cellular integrity was not impaired upon Ag-NP exposures. Minimal cytotoxicity, by measuring the release of lactate dehydrogenase, could only be detected following a higher concentrated AgNO3-solution. A release of pro-inflammatory markers TNF-alpha and IL-8 was neither observed upon Ag-NP and AgNO3 exposures as well as was not affected when cells were pre-stimulated with lipopolysaccharide (LPS). Also, an induction of mRNA expression of TNF-alpha and IL-8, could only be observed for the highest AgNO3 concentration alone or even significantly increased when pre-stimulated with LPS after 4 h. However, this effect disappeared after 24 h. Furthermore, oxidative stress markers (HMOX-1, SOD-1) were expressed after 4 h in a concentration dependent manner following AgNO3 exposures only. CONCLUSIONS: With an experimental setup reflecting physiological exposure conditions in the human lung more realistic, the present study indicates that Ag-NPs do not cause adverse effects and cells were only sensitive to high Ag-ion concentrations. Chronic exposure scenarios however, are needed to reveal further insight into the fate of Ag-NPs after deposition and cell interactions.

Does fog chemistry in Switzerland change with altitude?

During two extended summer seasons in 2006 and 2007 we operated two battery driven versions of the Caltech active strand cloud water collector (MiniCASCC) at the Niesen mountain (2362 m a.s.l.) in the northern part of the Swiss Alps, and two devices at the Lägeren research tower (690 m a.s.l.) at the northern boundary of the Swiss Plateau. During these two field operation phases we gained weekly samples of fog water, where we analyzed the major anions and cations, and the isotope ratios of fog water (in form of δ2H and δ18O). Dominant ions in fog water at all sites were NH4+, NO3−, and SO42 −. Compared to precipitation, the enrichment factors in fog water were in the range 5–9 at the highest site, Niesen Kulm. We found considerably lower summertime ion loadings in fog water at the two Alpine sites than at lower elevations above the Swiss Plateau. The lowest ion concentrations were found at the Niesen Kulm site at 2300 m a.s.l., whereas the highest concentrations (a factor 7 compared to Niesen Kulm) were found in fog water at the Lägeren site. Occult nitrogen deposition was estimated from fog frequency and typical fog water flux rates. This pathway contributes 0.3–3.9 kg N ha− 1 yr− 1 to the total N deposition at the highest site on Niesen mountain, and 0.1–2.2 kg N ha− 1 yr− 1 at the lower site. These inputs are the reverse of ion concentrations measured in fog due to the 2.5 times higher frequency of fog occurrence at the mountain top (overall fog occurrence was 25% of the time) as compared to the lower Niesen Schwandegg site. Although fog water concentrations were on the lower range reported in earlier studies, fog water is likely to be an important N source for Northern Alpine ecosystems and might reach values up to 16% of the total N deposition and up to 75% of wet N deposition by precipitation.

Erosion in relation to nutrition and the environment.

When considering the erosive potential of a food or drink, a number of factors must be taken into account. pH is arguably the single most important parameter in determining the rate of erosive tissue dissolution. There is no clear-cut critical pH for erosion as there is for caries. At low pH, it is possible that other factors are sufficiently protective to prevent erosion, but equally erosion can progress in acid of a relatively high pH in the absence of mitigating factors. Calcium and phosphate concentration, in combination with pH, determine the degree of saturation with respect to tooth minerals. Solutions supersaturated with respect to enamel or dentine will not cause them to dissolve, meaning that given sufficient common ion concentrations erosion will not proceed, even if the pH is low. Interestingly, the addition of calcium is more effective than phosphate at reducing erosion in acid solutions. Today, several calcium-enriched soft drinks are on the market, and acidic products with high concentrations of calcium and phosphorus are available (such as yoghurt), which do not soften the dental hard tissues. The greater the buffering capacity of the drink or food, the longer it will take for the saliva to neutralize the acid. A higher buffer capacity of a drink or foodstuff will enhance the processes of dissolution because more release of ions from the tooth mineral is required to render the acid inactive for further demineralization. Temperature is also a significant physical factor; for a given acidic solution, erosion proceeds more rapidly the higher the temperature of that solution. In recent years, a number of interesting potentially erosion-reducing drink and food additives have been investigated.

A stratigraphic framework for abrupt climatic changes during the Last Glacial period based on three synchronized Greenland ice-core records: refining and extending the INTIMATE event stratigraphy

Due to their outstanding resolution and well-constrained chronologies, Greenland ice-core records provide a master record of past climatic changes throughout the Last Interglacial–Glacial cycle in the North Atlantic region. As part of the INTIMATE (INTegration of Ice-core, MArine and TErrestrial records) project, protocols have been proposed to ensure consistent and robust correlation between different records of past climate. A key element of these protocols has been the formal definition and ordinal numbering of the sequence of Greenland Stadials (GS) and Greenland Interstadials (GI) within the most recent glacial period. The GS and GI periods are the Greenland expressions of the characteristic Dansgaard–Oeschger events that represent cold and warm phases of the North Atlantic region, respectively. We present here a more detailed and extended GS/GI template for the whole of the Last Glacial period. It is based on a synchronization of the NGRIP, GRIP, and GISP2 ice-core records that allows the parallel analysis of all three records on a common time scale. The boundaries of the GS and GI periods are defined based on a combination of stable-oxygen isotope ratios of the ice (δ18O, reflecting mainly local temperature) and calcium ion concentrations (reflecting mainly atmospheric dust loading) measured in the ice. The data not only resolve the well-known sequence of Dansgaard–Oeschger events that were first defined and numbered in the ice-core records more than two decades ago, but also better resolve a number of short-lived climatic oscillations, some defined here for the first time. Using this revised scheme, we propose a consistent approach for discriminating and naming all the significant abrupt climatic events of the Last Glacial period that are represented in the Greenland ice records. The final product constitutes an extended and better resolved Greenland stratotype sequence, against which other proxy records can be compared and correlated. It also provides a more secure basis for investigating the dynamics and fundamental causes of these climatic perturbations.

Ion fractionation in young sea ice from Kongsfjorden, Svalbard

The fractionation of major sea-water ions, or deviation in their relative concentrations from Standard Mean Ocean Water ratios, has been frequently observed in sea ice. It is generally thought to be associated with precipitation of solid salts at certain eutectic temperatures. The variability found in bulk sea-ice samples indicates that the fractionation of ions depends on the often unknown thermal history of sea ice, which affects the structure of pore networks and fate of solid salts within them. Here we investigate the distribution of ions in Arctic sea ice that is a few weeks old with a reconstructible thermal history. We separate the centrifugable (interconnected) and entrapped (likely disconnected) contributions to the ice salinity and determine their ion fractionation signatures. The results indicate that differential diffusion of ions, rather than eutectic precipitation of cryohydrates, has led to significant ion fractionation. The finding emphasizes the role of coupled diffusive–convective salt transport through complex pore networks in shaping the biogeochemistry of sea ice.

Coupling of LMS with a fs-laser ablation ion source: elemental and isotope composition measurements

Mass spectrometric analysis of elemental and isotopic compositions of several NIST standards is performed by a miniature laser ablation/ionisation reflectron-type time-of-flight mass spectrometer (LMS) using a fs-laser ablation ion source (775 nm, 190 fs, 1 kHz). The results of the mass spectrometric studies indicate that in a defined range of laser irradiance (fluence) and for a certain number of accumulations of single laser shot spectra, the measurements of isotope abundances can be conducted with a measurement accuracy at the per mill level and at the per cent level for isotope concentrations higher and lower than 100 ppm, respectively. Also the elemental analysis can be performed with a good accuracy. The LMS instrument combined with a fs-laser ablation ion source exhibits similar detection efficiency for both metallic and non-metallic elements. Relative sensitivity coefficients were determined and found to be close to one, which is of considerable importance for the development of standard-less instruments. Negligible thermal effects, sample damage and excellent characteristics of the fs-laser beam are thought to be the main reason for substantial improvement of the instrumental performance compared to other laser ablation mass spectrometers.