Investigation of mercury speciation in lichens.

Epiphytic lichens have long been considered to be reliable bioindicators of air pollution. In the present study only one lichen species, Hypogymnia physodes (L.) Nyl., was chosen; this species is very often used for biomonitoring in Europe. Total mercury and methylmercury were determined in lichens taken from various polluted and unpolluted locations in Slovenia, including a mercury mining area around Idrija. Additionally, total gaseous mercury in air was also determined at several sampling points.     

Extraction of arsenic compounds from lichens

Different extraction procedures were applied to improve the extraction efficiency of arsenic compounds from lichens. Two lichen species were chosen from an arsenic-contaminated environment: epiphytic Hypogymnia physodes (L.) Nyl. and terricolous Cladonia rei Schaer. Samples were extracted with water at temperatures of 20, 60 and 90 °C, using mixtures of methanol/water (9:1, 1:1 and 1:9), Tris buffer and acetone and the extracts speciated. Water and Tris buffer showed the best extraction efficiency of all extractants used; however, the extraction efficiency was still less than 23%. Since a major fraction of arsenic appeared to be associated with trapped soil particles, a sequential extraction procedure originally designed for soils (extraction steps: (1) 0.05 mol l⁻¹ (NH₄)₂SO₄; (2) 0.05 mol l⁻¹ (NH)₄H₂PO₄; (3) 0.2 mol l⁻¹ NH₄-oxalate buffer, pH 3.25; (4) mixture of 0.2 mol l⁻¹ NH₄-oxalate buffer and 0.1 mol l⁻¹ ascorbic acid, pH 3.25; (5) 0.5 mol l⁻¹ KOH) was applied and found to remove 45% of the total arsenic from H. physodes and 83% from C. rei. The lipid-soluble fraction of arsenic was estimated by k₀-INAA analysis of diethylether extracts and was found to be negligible. An HPLC-UV-HGAFS system was used to determine the arsenic compounds extracted. In both lichen species, arsenous acid, arsenic acid, monomethylarsonic acid, dimethylarsinic acid, arsenobetaine, trimethylarsine oxide and glycerol-ribose were detected. In addition, phosphate-ribose was found in H. physodes.     

Analytical and statistical analysis of elemental composition of lichens

The elemental composition of lichens from remote southern South America regions has been studied with analytical and statistical techniques to determine if the values obtained reflect species, growth forms or habitat characteristics. The enrichment factors are calculated discriminated by species and collection site and compared with data available in the literature. The elemental concentrations are standardized and compared for different species. The information was statistically processed, a cluster analysis was performed using the three first principal axes of the PCA; the three groups formed are presented. Their relationship with the species, collection sites and the lichen growth forms are interpreted.     

Non-destructive analysis of pigments and other organic compounds in lichens using Fourier-transform Raman spectroscopy: a study of Antarctic epilithic lichens

Lichens in Antarctic habitats are subjected to environmental extremes, including UVB radiation, desiccation and low temperatures, as well as to rapid fluctuations in these. Lichens synthesise a variety of chemical compounds in response to their environmental conditions which contribute towards their colour, and which act as protectants against physiological stresses. The fluorescence generated by the lichens at 532 nm can be used in epifluorescence microscopy to identify their presence on substrata but this can severely affect the Raman spectra using visible excitation. The advantage of the near infrared excitation used in FT-Raman spectroscopy in minimising fluorescence emission facilitates the molecular characterisation of lichen encrustations without having to remove the thallus from its substrate or remove or otherwise damage any part of the thallus. Spectroscopic biomarkers are proposed which allow the lichens to be characterised by the identification of characteristic lichen substances; the use of these biomarkers for the preliminary taxonomic identification of Antarctic lichens is examined and some potential pitfalls are described.     

Distribution of mercury in lichens across St. Charles, St. James, and St. John Parishes, Louisiana

Concentrations of mercury in the lichens Ramalina stenospora and Parmotrema praesorediosum were determined using a Bacharach Model 50B analyzer system employing the Environmental Protection Agency (EPA) cold vapor atomic absorption method. Samples were collected from the limbs of live oak trees in a three-parish area in south-east Louisiana. The highest concentrations detected were above 0.8 ppm (μg/ml) and fell off rapidly with increasing distance from possible sources of trace metals. The spatial distribution of mercury concentrations correlated with predominant wind patterns for the region.     

Fatty-acid and phospholipid composition of lichens of the Volga basin

The composition of the fatty acids and phospholipids of 16 species of lichens collected in the basin of the river Volga has been studied. The main phospholipid was phosphatidylcholine the amount of which ranged in the various species from 33.3 to 85.5% of the total phospholipids. Other phospholipids were also found: phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol. The main fatty acids were the 16:0, 18:0, and 18:1 varieties. Institute of the Ecology of the Volga Basin, Russian Academy of Sciences, Tol'yatti. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 613–615, September–October, 1991.     

Fatty-acid and phospholipid composition of lichens of the Volga basin

The composition of the fatty acids and phospholipids of 16 species of lichens collected in the basin of the river Volga has been studied. The main phospholipid was phosphatidylcholine the amount of which ranged in the various species from 33.3 to 85.5% of the total phospholipids. Other phospholipids were also found: phosphatidylethanolamine, phosphatidylserine, phosphatidylinositol, and phosphatidylglycerol. The main fatty acids were the 16:0, 18:0, and 18:1 varieties.Institute of the Ecology of the Volga Basin, Russian Academy of Sciences, Tol'yatti. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 613–615, September–October, 1991.     

Potential of lichens for monitoring iodine-129 and chlorine-36

Chlorine-36 (half life 3.01 × 10⁵ year), a beta emitter, is produced naturally but its presence has been enhanced by atmospheric weapons testing and other nuclear activities. Iodine-129 has a half life of 1.57 × 10⁷ years and is also produced by nuclear activities, in particular fuel reprocessing. Many elements have a long biological half-life in lichens, which were thus investigated so as to assess their suitability for ³⁶Cl and ¹²⁹I monitoring. Lichens sampled between 1998 and 2008 were analysed for total chlorine, and selected samples were processed for ³⁶Cl measurement using Accelerator Mass Spectrometry (AMS); ¹²⁹I was analyzed by gamma spectrometry. Different aspects are discussed: long-term storage in lichens versus environmental mobility, levels in samples collected near a reprocessing facility, and potential for spatial and temporal monitoring.     

Raman spectroscopy of hot desert, high altitude epilithic lichens

Twenty-three highly-coloured lichen specimens belonging to the genera Candelariella, Aspicilia and Xanthoria from high altitude sites in the Atacama Desert, Chile, 2300-4500 metres, have been analysed non-destructively by Raman spectroscopy. The vibrational band assignments in the spectra of the specimens, which were still attached to their limestone or sandstone substrata, were accomplished by comparison with the chemical compositions obtained from wet chemical extraction methods. Carotenoids and chlorophyll were found in all specimens as major components and the characteristic spectral signatures of calcium oxalate monohydrate (whewellite) and dihydrate (weddellite) could be identified; chemical signatures were found for these materials even in lichen thalli growing on the non-calcareous substrata, indicating probably that the calcium was provided here from wind- or rain-borne sources. The Raman spectral biomarkers for a variety of protective biomolecules and accessory pigments such as usnic acid, calycin, pulvinic acid dilactone and rhizocarpic acid have been identified in the lichens, in broad agreement with the chemical extraction profiles. The present study indicates that some form of non-destructive taxonomic identification based on Raman spectroscopy was also possible.     

Investigation of semi-thin cryosections of lichens by laser microprobe mass spectrometry

The application of the laser microprobe mass spectrometry to the in-situ characterization of organic aromatic constituents in cryosections of microlichens is described. The samples were photographed before and after microprobe measurement by fluorescence microscopy or transmission electron microscopy to obtain more detailed information on the histological distribution of the compounds examined within the biological structures. This new technology has major advantages for integrated study of the morphology, anatomy and chemistry of plants.