New Interpretative Scales for Lichen Bioaccumulation Data: The Italian Proposal

Abstract

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 “bioaccumulation scales” 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, “Absence of”, “Low”, “Moderate”, “High”, and “Severe” 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.

Magnetic Emissions from Brake Wear are the Major Source of Airborne Particulate Matter Bioaccumulated by Lichens Exposed in Milan (Italy)

“…Lichen thalli transplanted at the control site showed values (Table 1) well within the range of background concentrations for this species [29]. After 3 months of exposure in Milan, samples of E. prunastri exhibited accumulation for all elements at all sites, with very few exceptions (Table 1), with mean values exceeding those of the control sample by a factor 1.2 (Cd) to 6.3 (Sb).…”

Estimating Environmental Contamination and Element Deposition at an Urban Area of Central Italy

“…In bioccumulation studies, the technique of lichen transplants, i.e., samples taken from an unpolluted site and transferred to the study area, has several advantages over the use of native samples: It overcomes the limit of the absence of native lichens in heavily polluted areas (and also in urban contexts), the exposure time is known, and the interpretation of the results can be based on pre-exposure (control) values [9]. Furthermore, the interpretation of lichen bioaccumulation data becomes of paramount importance in decision-making processes and environmental forensics, requiring standardized procedures that account for data uncertainty and produce clear outcomes [6,7,10].…”

“…In this study, we investigated the bioaccumulation of selected trace elements in lichen samples transplanted for three months in an urban area of Central Italy and delineated, by integrating recently proposed interpretative methods [6,10], the main environmental contaminants, their sources, and fluxes of element depositions in lichens converted as estimates of their average annual deposition rates.…”

Congruence Evaluation of Mercury Pollution Patterns Around a Waste Incinerator over a 16-Year-Long Period Using Different Biomonitors

“…Although BSs' results can be used to easily describe the spatial and temporal pattern of Hg emissions in a given area, a proper way to use these data in order to estimate the exact Hg air concentrations seems to remain a problem without a solution [56,57]. Nevertheless, in order to contextualize the magnitude of the observed pollution scenario, the results of active and passive BSs based on lichens can be expressed as a function of the species-specific background elemental content (BEC; [58][59][60]). This allows researchers to evaluate pollution phenomena as a relative difference between the pollutant concentrations measured in lichen samples exposed in a polluted area and those collected in unpolluted, background areas (EC ratio, see the work of [61]; now EU ratio, see the work of [60]).…”

“…Nevertheless, in order to contextualize the magnitude of the observed pollution scenario, the results of active and passive BSs based on lichens can be expressed as a function of the species-specific background elemental content (BEC; [58][59][60]). This allows researchers to evaluate pollution phenomena as a relative difference between the pollutant concentrations measured in lichen samples exposed in a polluted area and those collected in unpolluted, background areas (EC ratio, see the work of [61]; now EU ratio, see the work of [60]). If these concepts would be applied to our data, we might classify the observed pollution scenario as an event causing an increase of Hg concentration circa 6.4, 24, and 4 times higher than the usual Hg content observable in the native population of X. parietina, P. furfuracea (pre-exposure values; see the work of [18]), and R. pseudoacacia, respectively.…”