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

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.

Mercury Content and Amelioration of Its Toxicity by Nitric Oxide in Lichens

“…Owing to the low Hg amount in Evernia prunastri mentioned above and its soft thalli suitable for biochemical extraction, we selected this species for subsequent investigation focused on the toxicity of exogenous Hg and cross-talk with nitric oxide (see representative photo of Evernia thalli in Supplementary Figure S1 ). Total Hg content was not affected by SNP co-application, with an average value of 2.4 mg Hg/g DW, which is similar to data reported by Vannini et al [ 13 ] who also found over 2 mg Hg/g DW in the same species after 1 h of immersion in 100 µM Hg solution, as did we ( Figure 1 ). Lichen Ramalina farinacea , with similar fruticose thalli exposed to 100 µM Cd under identical exposure conditions, also contained close to 2 mg Cd/g DW [ 24 ], while terrestrial lichens Cladonia and Peltigera , exposed to 100 µM Hg under similar exposure conditions, contained over 1 mg Hg/g DW [ 12 ]; therefore, the sorption of metals seems to be affected by the applied concentration mainly.…”

“…Lichens are not plants, but lichenized fungi with their body (thallus) typically formed by the symbiotic association between fungus and green alga. Despite more common works focused on the use of lichens for biomonitoring of metallic pollution including the occurrence of Hg [ 6 , 7 , 8 , 9 , 10 , 11 ], physiological studies are rare [ 12 , 13 ].…”

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

“…Currently, the use of biochar in the environmental field concerns both the reduction of PTE mobility in soils to increase the edibility of crop products [ 28 , 29 ] and the removal of heavy metals from wastewater [ 31 , 32 ]. However, based on the results obtained in this study, its ability to provide information on the environmental availability of heavy metals such as Cd should not be ruled out, especially when it comes to water bodies.…”

“…Biochar (BC), the by-product of the pyrolysis of organic materials (often wood) for bioenergy production, is now attracting considerable attention, from an environmental perspective, as a strategy to stabilize PTEs in soils [ 27 , 28 , 29 ], thereby enabling their remediation [ 30 ]; as a tool for filtering contaminated water and air [ 31 , 32 , 33 ]; and as a sustainable strategy for agricultural purposes [ 34 , 35 ]. Despite these diverse applications, the potential of BC for environmental biomonitoring has been surprisingly underexplored.…”

“…There is extensive research in the literature on the ability of lichens to accumulate Cd (see [20,26] for examples), but there is no information on the fate of this metal after its environmental availability has been reduced. Biochar (BC), the by-product of the pyrolysis of organic materials (often wood) for bioenergy production, is now attracting considerable attention, from an environmental perspective, as a strategy to stabilize PTEs in soils [27][28][29], thereby enabling their remediation [30]; as a tool for filtering contaminated water and air [31][32][33]; and as a sustainable strategy for agricultural purposes [34,35]. Despite these diverse applications, the potential of BC for environmental biomonitoring has been surprisingly underexplored.…”