Search

The lichen Usnea articulata collected from an unpolluted area was exposed for 6 months at 26 sites for the sample chosenusing a stratified random design, and the content of potentially toxic elements (PTEs) including As, Cd, Cr, Cu, Fe, Hg, Mn, Mo, Ni, Pb, Sn, V, and Zn, was assessed using ICP-MS. The health risk for both adults and children was then calculated using the PTEs concentrations. The results showed that despite the hostile urban conditions, transplanted lichens depicted clear deposition patterns of airborne PTEs, mostly associated with industrial sites, where As and other elements showed remarkably high values. The cumulative hazard index was below the risk threshold, both for adults and children. For the entire population (particularly children) residing in areas surrounding industrial sites, As and Cr appeared to be potentially carcinogenic elements.

In bioaccumulation studies, sample devitalization through acid washing or oven drying is commonly applied to enhance the element accumulation efficiency of moss sample. Such aspect, however, has never been considered in biomonitoring surveys using lichens. In this study, the trace element accumulation performance of living (L) and dead (D) samples of the lichen Pseudevernia furfuracea was compared by a side-by-side transplanting at 40 sites in a large, mixed land use area of NE Italy for 8 weeks. Devitalization was achieved without any physico-chemical treatments, by storing lichen samples in a dark cool room for 18 months. Health status of lichens was assessed before and after the sample exposure by chlorophyll fluorescence emission. Although elemental analysis of the two exposed sample sets revealed a similar trace element pollution scenario, the content of 13 out of the 24 selected elements was higher in D samples. By expressing results as exposed-to-unexposed (EU) ratio, D samples show a higher bioaccumulation signal in 80% of transplant sites for Al, Ca, Fe, Hg, Pb and Ti. Overall, the health status of lichen samples might lead to interpretational discrepancies when EU ratio is classified according to the recently proposed bioaccumulation scale.

This research focuses on the methodological standardization of bioaccumulation techniques by lichens. The leitmotif of this work is a biomonitor of airborne trace elements and other contaminants, the lichen Pseudevernia furfuracea (L.) Zopf, that was here repeatedly selected as test species. Firstly, the background element concentration values (BECs) for such species were assessed, since these are a prerequisite for the assessment of trace element pollution, by a large sampling effort over the Italian territory. In a first contribution, the occurrence of BEC differences of the two varieties of P. furfuracea (var. furfuracea and var. ceratea) was assessed using samples from remote areas. After having proved the absence of significant element content differences ascribable to taxonomic traits, in a second study, it was demonstrated that environmental descriptors were predictive of BECs, and these were provided for environmentally homogeneous Italian macro-regions. In this phase, the analytical outcomes of two acid mixtures for sample mineralization (i.e., a total digestion with hydrofluoric acid and a partial, aqua regia-based one) were also compared. The total digestion showed a better performance for the majority of elements. Two sets of digestion-specific BECs were provided, to be used as references in biomonitoring applications, depending on the selected mineralization procedure. Other approaches can be used to interpret bioaccumulation data. Case in point are the so-called “interpretative scales”. New scales for native lichens and transplants were respectively built up by analyzing the distribution of ratios between element concentration data and species-specific background concentration references (B ratio), contextually provided for two foliose lichens (Flavoparmelia caperata and Xanthoria parietina) and that of ratios between element concentration in exposed and unexposed samples (EU ratio) of two fruticose lichens (Evernia prunastri and Pseudevernia furfuracea). The new scales overcome critical points affecting previous ones. The second part of this research focuses on aspects related to the functioning of the lichen symbiosis, still using P. furfuracea as test species. Firstly, the effects of ozone (O3) on the physiology of previously field-stressed P. furfuracea samples were assessed. Samples were exposed for 6 weeks at sites with different levels of particulate and polycyclic aromatic hydrocarbon (PAH) emissions. Afterwards, samples were transferred to fumigation chambers, where they were O3-treated for 2 weeks. Physiological markers, elemental and PAH concentrations were measured in matched replicate sets at each experimental step. The O3-tolerance of the test species was proved, and interestingly, the content of some PAHs in samples with the highest enrichment levels significantly lowered after the ozonation, suggesting a role of O3 in degrading accumulated PAHs, with potential interpretative repercussions in transplant-based surveys aimed at evaluating PAH depositions in case of high O3 ground levels. A second contribution addresses a frequently investigated aspect for mosses, but not for lichens. Indeed, devitalization procedures are standardly carried out on moss samples, since these enhance the elemental capture by passive uptake processes. In this study, the accumulation performance of living and dead P. furfuracea samples is assessed through a high sample-sized transplant. Paired living-dead samples were exposed for 8 weeks at 40 sites in a study area of NE Italy. The two sample sets, consistently described low deposition levels over the study area, however, higher accumulation signals were revealed in dead lichens. When sites were classified according to the new bioaccumulation scale, some interpretational discrepancies arose, therefore the possibility of sample devitalization should be seriously considered, also to contribute to the methodological harmonization of biomonitoring techniques.

The concentration of selected trace elements and the magnetic properties of samples of the lichen Evernia prunastri exposed for 3 months in Milan (Italy) were investigated to test if magnetic properties can be used as a proxy for the bioaccumulation of chemical elements in airborne particulate matter. Magnetic analysis showed intense properties driven by magnetite-like minerals, leading to significant correlations between magnetic susceptibility and the concentration of Fe, Cr, Cu, and Sb. Selected magnetic particles were characterized by Scanning Electron Microscope and Energy Dispersion System microanalyses, and their composition, morphology and grain size supported their anthropogenic, non-exhaust origin. The overall combination of chemical, morphoscopic and magnetic analyses strongly suggested that brake abrasion from vehicles is the main source of the airborne particles accumulated by lichens. It is concluded that magnetic susceptibility is an excellent parameter for a simple, rapid and cost-effective characterization of atmospheric trace metal pollution using lichens.

The interpretation of lichen bioaccumulation data is of paramount importance in environmental forensics and decision-making processes. By implementing basic ideas underlying previous interpretative scales, new dimensionless, species-independent &ldquo, bioaccumulation scales&rdquo, for native and transplanted lichens are proposed. Methodologically consistent element concentration datasets were populated with data from biomonitoring studies relying on native and transplanted lichens. The scale for native lichens was built up by analyzing the distribution of ratios between element concentration data and species-specific background concentration references (B ratios), herein provided for Flavoparmelia caperata and Xanthoria parietina (foliose lichens). The scale for transplants was built up by analyzing the distribution of ratios between element concentration in exposed and unexposed samples (EU ratio) of Evernia prunastri and Pseudevernia furfuracea (fruticose lichens). Both scales consist of five percentile-based classes, namely, &ldquo, Absence of&rdquo, &ldquo, Low&rdquo, Moderate&rdquo, High&rdquo, and &ldquo, Severe&rdquo, bioaccumulation. A comparative analysis of extant interpretative tools showed that previous ones for native lichens suffered from the obsolescence of source data, whereas the previous expert-assessed scale for transplants failed in describing noticeable element concentration variations. The new scales, based on the concept that pollution can be quantified by dimensionless ratios between experimental and benchmark values, overcome most critical points affecting the previous scales.

The seasonal differences of the polycyclic aromatic hydrocarbons (PAHs) content in lichen transplants were investigated in an area of ca. 40 square kilometers in NE Italy characterized by different land use. Two sets of samples of the epiphytic lichen Pseudevernia furfuracea were collected in a pristine area of the Carnic Alps and transplanted to 40 exposure sites for a period of two months, respectively in late winter and in summer. Results revealed a pronounced difference between the two seasons in terms of PAH content and distribution patterns. After the summer exposure the PAH concentrations in the transplants were more than one order of magnitude lower than after the winter exposure (ranging from 48.22 to 272.73 ng g−1 dw and from 289.73 to 1575.85 ng g−1 dw in the summer and winter samples respectively). Also the main emission sources changed, mostly due to the drastic reduction in the emissions by wood burning for domestic heating and to the different meteorological conditions. In summer PAHs degradation was enhanced by intense UV radiation, high temperatures, and presence of ozone. The implications of these findings for the biomonitoring of PAHs pollution are addressed.