Mark R. D. Seaward

Correlation between the nitrogen concentration of two epiphytic lichens and the traffic density in an urban area

A field experiment was carried out in the urban environment of the Grenoble area using two epiphytic lichens: the nitrophytic Physcia adscendens and the acidiphytic Hypogymnia physodes. Two complementary studies characterized this experiment. Firstly, a sampling of the two lichens in 48 sites randomly located throughout the Grenoble area indicated that roads (size and proximity to sampling sites) influenced the nitrogen concentrations of P. adscendens, but not those of H. physodes. Secondly, to study more accurately the influence of roads, a traffic index was calculated and applied along two transects located perpendicularly to urban motorways. Significant positive correlations were found between this traffic index and the total nitrogen concentration of P. adscendens.

The date palm (Phoenix dactylifera L.) as a biomonitor of lead and other elements in arid environments

The date palm (Phoenix dactylifera L.) has been tested as a possible biomonitor of metal pollution in Riyadh city, Saudi Arabia. The metal content (Pb, Zn, Cu, Ni, Cr and Li) was determined for washed and unwashed leaflets collected from a wide range of sites with different degrees of metal pollution (urban, suburban, highway and industrial areas) and from a rural (control) site. Differences between washed and unwashed samples revealed that metal pollutants exist as superficial contaminants, especially levels of Pb and Zn, which varied according to the metal source. However, P. dactylifera leaflets were found to be suitable biomonitors for metal pollution in Riyadh and similar arid and semi-arid environments.

Calcium oxalate in lichen biodeterioration studied using FT-Raman spectroscopy

Abstract The biodeterioration of diverse natural and man-made substrata by Caloplaca aurantia, Lecanora muralis and Acarospora oxytoma has been studied using FT-Raman spectroscopy with 1064 nm laser excitation. Each of the three lichen species produce relatively large amounts of calcium oxalate in encrustations at the thallus—substratum interface during the biodeterioration process; the Raman spectroscopic technique is capable of identifying non-destructively the monohydrate, with ν(CO) stretching bands at 1463 and 1496 cm−1 and the dihydrate, with a ν(CO) stretching band at about 1475 cm(su−1). In this work, the presence of calcium oxalate monohydrate and dihydrate in the lichen encrustations is identified for these high-oxalate producing biodeteriorative lichen systems. The results indicate that the lichens adopt different methods for the production and removal of the hydrated calcium oxalates in the encrustations.

BIOLOGICAL ORIGIN OF MAJOR CHEMICAL DISTURBANCES ON ECCLESIASTICAL ARCHITECTURE STUDIED BY FOURIER TRANSFORM RAMAN SPECTROSCOPY

Lichens, formerly considered as weathering agents in a geological context, are shown to be capable of biodeteriorating stone substrata within a relatively short time-scale. Detailed Raman spectroscopic studies have demonstrated the highly destructive properties of calcium oxalate produced by lichen thalli. Dirina massiliensis forma sorediata is capable of chemically disturbing substrata to depths of almost 2 mm in under 12 years and converting the substrata into substantial quantities of calcium oxalate. Studies of disfigurement of English church walls assumed to have been rendered with a decorative or protective surface via restoration, have also been proved spectroscopically to be the result of this lichen’s biodeteriorative action.

Raman spectra of oxalates in lichen encrustations on Renaissance frescoes

Abstract The vibrational Raman spectra of lichen encrustations on biodeteriorated Renaissance frescoes have been recorded using a laser Raman microprobe. The major chemical species identified in the encrustations is calcium oxalate. Other vibrational features in the Raman spectra have been assigned to fragments of the substratum incorporated from the biodeterioration process and to organic by-products of lichen metabolism such as erythrin, lecanoric acid and meso -erythritol.

Particle size effect for metal pollution analysis of atmospherically deposited dust

The metallic compositions of 231 atmospherically deposited dust samples obtained from widely-differing environments in Riyadh city, Saudi Arabia, have been investigated in relation to the particle size distributions. Sample data are presented which show that particle size classification is very important when analysing dust samples for atmospheric metal pollution studies. By cross-correlation and comparison, it was found that the best way to express the results of the metal concentration trend was as an average of particle ratios. Correlations between the six metals studied, namely Pb, Cr, Ni, Cu, Zn and Li, were found for every particle size (eight categories) and reveal that the metal concentrations increased as the particle size decreased. On the basis of this work, it is strongly recommended that future international standards for metal pollutants in atmospherically deposited dusts should be based on particle size fractions.

Lichen biodeterioration under different microclimates: an FT Raman spectroscopic study

Abstract The FT Raman spectra of lichen-substratum encrustations of Diploicia canescens on a limestone church tower are reported. The presence of calcium oxalate dihydrate in the encrustations was identified from the ν (CO) stretching fundamentals at 1474, 908 and 506 cm −1 of the oxalate ion. Quantitative measurements were made of the relative amounts of lichen cellulose, characterised by ν (CH) stretching at 2934 cm −1 , pigmentation, characterised by ν (CC) stretching at 1526 cm −1 , and calcium oxalate dihydrate along radial transects of surfaces of lichen thalli and encrustations. It was found that the biodeterioration of the limestone substratum did not involve the incorporation of particles of the substratum into the central zone of the thallus, unlike other high-oxalate producing lichen species. A preliminary investigation has been made of the relationship between microclimate, in terms of air and wall temperatures and humidity, and the biodeteriorative capability of thalli exemplified by calcium oxalate dihydrate production: it would appear that warmer and drier sites are more conducive to calcium oxalate dihydrate production by D . canescens under these circumstances.

Lichen Recolonization of Trees in the Jardin du Luxembourg, Paris

A recent survey of epiphytic lichens in the Jardin du Luxembourg has shown there to be a marked improvement in the air quality of Paris over the past decade. Recolonization by at least 11 lichen species has occurred during that period. It has taken almost 100 years for epiphytic lichens to re-establish in the Jardin du Luxembourg, where William Nylander in the 1890s was able to amply confirm his far reaching hypothesis, made 30 years earlier, on the direct relationship between lichen survival and air pollution.

The role of lichens in the biodeterioration of ancient monuments with particular reference to central Italy

Abstract A critical appraisal is made of the part played by lichens in the deterioration of a wide range of archaeological materials. Stone- and art- work in exposed and partially enclosed environments were examined to identify those most vulnerable to attack. Assessment was made of the relationships between particular species and the physical and chemical nature of their substrata, to establish those species responsible for disfigurement and those causing damage. Particular attention was paid to recent environmental changes conductive to lichen invasion of terracotta, mortar and painted plaster.

Preliminary Raman microscopic analyses of a lichen encrustation involved in the biodeterioration of renaissance frescoes in Central Italy

Raman microscopic analysis has proved effective in the interpretation and characterization of both the physical and chemical nature of the lichen/substratum system. In the case of Dirina massiliensis forma sorediata, a lichen causing extensive damage to Italian frescoes, the lichen-generated encrustation has been proved to be composed essentially of calcium oxalate. This particular biodeterioration process may be slowed down, or indeed inhibited, by the presence of certain compounds, as yet undertermined, used in the preparation of surfaces and the painting of frescoes. From a conservators point of view, Raman microscopic analysis uses microscopic samples in the nanogram-picogram range and is non-destructive of the sample.