Persistent mercury hot spot in Central Europe and Skalka Dam reservoir as a long-term mercury trap.

This study aimed to evaluate the relevance of the floodplain pollution sinks of the legacy mercury (Hg) hot spot in Kössein-Röslau river system (east Bavaria, Germany) for further mobilisation and fluvial transport of mercury in suspended particulate matter (SPM), as an important transport medium of Hg in aquatic systems. The channel belt fluvial erosion as the secondary pollution pathway was also considered. The hot spot has originated from the production of Hg compounds such as C2H5HgCN and C6H5HgCl in Chemical Factory Marktredwitz, and even more than 30 years after the factory abandonment, the Kössein and the Röslau rivers still export polluted fine grained SPM (median 25-35 µm) with mean annual concentrations of 17.4 mg/kg. SPM sampling was performed by floating samplers, supported by floodplain drill cores and by recent channel sediments manually collected along the polluted rivers further. Based on long-term monitoring data set from state enterprise Povodí Ohre, fish in the Skalka Reservoir have had Hg concentrations in their muscles up to 6 mg/kg for at least the last 14 years, exceeding the European maximal limit of 0.5 mg/Hg/kg. In addition, the Hg inventory in the Kössein-Röslau river stretches was therefore calculated; it produced an estimate of ca. 21 t Hg in a 22-km-long channel belt, prone to fluvial remobilisation during floods. Although a major portion of the fluvially transported Hg has yet been trapped by the Skalka Reservoir, the Hg content in the SPM exported farther downstream still varies between 2 and 10 mg/kg Hg. Due to the considerable Hg inventory in the Kössein-Röslau rivers, an improvement will not occur downstream unless specific measures target the secondary pollution mechanism(s).

Robust assessment of moderate heavy metal contamination levels in floodplain sediments: a case study on the Jizera River, Czech Republic.

Enrichment factors for Cr, Cu, Ni, Pb and Zn in floodplain fines from the middle and the lower courses of the Jizera River (a tributary of the Elbe River in the Czech Republic) were evaluated to compare the original contamination profiles with post-depositional and pedogenic changes. Background concentrations of heavy metals were assessed from uncontaminated sediments (soils) in the study area that belong to the same sedimentary facies and were not affected by reductimorphic processes. Facies assignment is accessible by geophysical imaging combined with core analysis. Sediments from point bars and channel banks in direct contact with riverine water are more heavily polluted than overbank fines from the distal floodplain. The point pollution source, a century-old battery and car production facility in the city of Mladá Boleslav, has certainly been responsible for Ni and Cr pollution, contributed substantially to Cu and Pb pollution, and had a less significant effect on the Zn enrichment factor. Although the use of soil enrichment factors has been criticized, these factors help to manage hydraulic sorting and recognition of post-depositional migration in soil profiles of floodplain sediments. When moderate pollution (enrichment factor about 1.5 for Cu, Pb and Zn) is found, background concentrations must be carefully evaluated and natural enrichment must be taken into account. Studies of such small enrichment factors contribute to the understanding of the dispersal and fates of pollutants in floodplains.

Fluorescence of reduced charge montmorillonite complexes with methylene blue: Experiments and molecular modeling.

The intensity of fluorescence of montmorillonites fully saturated by methylene blue (MB) is very poor due to energy dissipation in MB aggregates. A series of reduced charge montmorillonites (RCM) were prepared from Na-homoionic SWy and Ca homoionic SAz with the aim to decrease the MB aggregation. Fine tuning MB adsorption degree by charge reduction and MB concentration enabled controlled production of different dye species from aggregates via dimers to monomers. It was shown that the intensity of the fluorescence of low-loaded MB-RCM complexes is enhanced by several orders of magnitude with respect to dye-saturated original montmorillonites. XRD analyses, molecular modeling, and diffuse reflectance spectroscopy revealed that low MB-loaded RCMs are very probably adsorbed mainly on the external montmorillonite surface as isolated dye molecules. Such a state cannot be achieved in the solid state without very careful tailoring of the host-guest interaction.

Analysis of organic colouring and binding components in colour layer of art works.

Two methods of analysis of organic components of colour layers of art works have been tested: IR microspectroscopy of indigo, Cu-phthalocyanine, and Prussian blue, and MALDI-TOF-MS of proteinaceous binders and a protein-containing red dye. The IR spectra distortion common for smooth outer surfaces and polished cross sections of colour layer of art works is suppressed by reflectance measurement of microtome slices. The detection limit of the three blue pigments examined is approximately 0.3 wt% in reference colour layers in linseed oil binder with calcite as extender and lead white as a drying agent. The sensitivity has been sufficient to identify Prussian blue in repaints on a Gothic painting. MALDI-TOF-MS has been used to identify proteinaceous binders in two historical paintings, namely isinglass (fish glue) and rabbit glue. MALDI-TOF-MS has also been proposed for identification of an insect red dye, cochineal carmine, according to its specific protein component. The enzymatic cleavage with trypsin before MALDI-TOF-MS seems to be a very gentle and specific way of dissolution of the colour layers highly polymerised due to very long aging of old, e.g. medieval, samples.