Uptake and release of copper ions in epiphytic lichens

Accumulation and Release of Cadmium Ions in the Lichen Evernia prunastri (L.) Ach. and Wood-Derived Biochar: Implication for the Use of Biochar for Environmental Biomonitoring

Biochar (BC) boasts diverse environmental applications. However, its potential for environmental biomonitoring has, surprisingly, remained largely unexplored. This study presents a preliminary analysis of BC's potential as a biomonitor for the environmental availability of ionic Cd, utilizing the lichen Evernia prunastri (L.) Ach. as a reference organism. For this purpose, the lichen E. prunastri and two types of wood-derived biochar, biochar 1 (BC1) and biochar 2 (BC2), obtained from two anonymous producers, were investigated for their ability to accumulate, or sequester and subsequently release, Cd when exposed to Cd-depleted conditions. Samples of lichen and biochar (fractions between 2 and 4 mm) were soaked for 1 h in a solution containing deionized water (control), 10 µM, and 100 µM Cd2+ (accumulation phase). Then, 50% of the treated samples were soaked for 24 h in deionized water (depuration phase). The lichen showed a very good ability to adsorb ionic Cd, higher than the two biochar samples (more than 46.5%), and a weak ability to release the metal (ca. 6%). As compared to the lichen, BC2 showed a lower capacity for Cd accumulation (-48%) and release (ca. 3%). BC1, on the other hand, showed a slightly higher Cd accumulation capacity than BC2 (+3.6%), but a release capacity similar to that of the lichen (ca. 5%). The surface area and the cation exchange capacity of the organism and the tested materials seem to play a key role in their ability to accumulate and sequester Cd, respectively. This study suggests the potential use of BC as a (bio)monitor for the presence of PTEs in atmospheric depositions and, perhaps, water bodies.

Accumulation of Cadmium in Transplanted Lichen Pyxine cocoes (Sw.) Nyl., with Reference to Physiochemical Variation and Kinetics of Cadmium Biosorption

The present study aims to signify the role of Pyxine cocoes (Sw.) Nyl. (P. cocoes) as cadmium (Cd) biomonitor in atmosphere. This was achieved by quantifying the amount of Cd accumulated in transplanted P. cocoes, when stimulated with known concentrations of Cd (5µM, 50µM, 100µM, 150µM and 200µM) at increasing intervals of time up-to 40 days. All the five concentrations exhibited increasing trend of accumulation with time. As depicted by Pearson's Correlation (at p < 0.001), anti-oxidative enzymes (superoxide dismutase r= -0.812, ascorbate peroxidase r= -0.802, catalase r= -0.757) and electrical conductivity (r = 0.693) were the most efficient parameters to depict increased Cd presence in atmosphere. In the current study, accumulation of Cd by transplanted lichen has been first time analyzed by biosorption kinetics. The uptake of Cd by P. cocoes followed pseudo-second-order kinetics (range of R₂² value was 0.969-0.998). The marker parameters in combination with the ability to accrue Cd fortifies P. cocoes's role as a biomonitor.

Accumulation and Release of Mercury in the Lichen Evernia prunastri (L.) Ach

Simple Summary

Lichens are among the most used and most effective biomonitors of airborne mercury (Hg); however, although the ability of lichens to take up Hg and provide accurate patterns of Hg contamination around emission sources is well documented, information on their ability to reflect the decreasing environmental availability of this element is minimal and contrasting. The aim of this study was to investigate both the accumulation and release of Hg²⁺ in lichens, using Evernia prunastri as a model species, and hypothesizing that 24 months is sufficient for treated samples to return to background values. The results of this study highlighted the ability of the lichen E. prunastri to reflect very quickly the available Hg concentration, as well as to indicate an ameliorated situation (e.g., the closure of an Hg source). However, we have found evidence that an acute pollution episode can influence the content of Hg in lichens for several years.

Abstract

This study investigated the dynamics of the accumulation and release of Hg²⁺ in lichens, using Evernia prunastri (L.) Ach. as a model species. Thalli were incubated with solutions containing 1, 10, and 100 µM Hg²⁺ and then exposed for 1, 2, 3, 6, 12, 18, and 24 months at the Botanical Garden of the University of Siena (a location free from local Hg sources). Lichen samples accumulated Hg proportionally to the exposure concentration, and after the exposure, reductions over time were evident, already starting from 1–2 months. After 24 months, samples released 72–74 (healthy thalli) to 94% (unhealthy thalli) of the accumulated Hg, but control values of untreated samples were never reached. Depending on the Hg content after the exposure, stable decreased concentrations were reached after 6–24 months. The results of this study highlight the ability of the lichen E. prunastri to reflect rapidly increasing environmental Hg concentrations, as well as to indicate an ameliorated situation (e.g., the closure of an Hg source). However, we have found evidence that an acute pollution episode can influence the content of Hg in lichens for several years.

Modeling heavy metal release in the epiphytic lichen Evernia prunastri

In this study, the release of Cu²⁺ and Zn²⁺ was investigated and modeled in the epiphytic lichen Evernia prunastri. Samples were incubated with solutions containing these metals at ecologically relevant concentrations (10 and 100 μM) and then transplanted to a remote area and retrieved after 1, 2, 3, 6, 12, and 18 months. The results showed that, after 12 months, all samples faced similar metal reductions of ca. 80-85%, but after this period, all the involved processes seem to be no longer capable of generating further reductions. These results suggest that the lichen E. prunastri can provide information about environmental improvements after exposure to high or very high pollution levels in a relatively short period of time.

Can Chitin and Chitosan Replace the Lichen Evernia prunastri for Environmental Biomonitoring of Cu and Zn Air Contamination?

This study compared the ability of the lichen Evernia prunastri, chitin and chitosan to take up Cu²⁺ and Zn²⁺. It was hypothesized that chitin and chitosan have an accumulation capacity comparable to the lichen, so that these biopolymers could replace the use of E. prunastri for effective biomonitoring of Cu and Zn air pollution. Samples of the lichen E. prunastri, as well as chitin (from shrimps) and chitosan (from crabs), were incubated with Cu and Zn solutions at concentrations of 0 (control), 10, 25, 50, 75, and 100 µM and analyzed by Inductively Coupled Plasma Mass Spectrometry (ICP-MS). Metal concentrations accumulated by lichen, chitin and chitosan samples were strongly and linearly correlated with the concentrations in the treatment solutions. The lichen always showed significantly higher accumulation values compared to chitin and chitosan, which showed similar accumulation features. The outcomes of this study confirmed the great effectiveness of the lichen Evernia prunastri for environmental biomonitoring and showed that chitin and chitosan have a lower accumulation capacity, thus suggesting that although these biopolymers have the potential for replacing E. prunastri in polluted areas, their suitability may be limited in areas with intermediate or low pollution levels.