Mercury in epiphytic lichens of the Crimean peninsula

Current environmental concerns are associated with elevated levels of mercury (Hg) contamination, and monitoring studies are needed to estimate mercury atmospheric emissions as one of the hazardous global pollutants. Therefore, epiphytic lichens could be used as the most sensitive bioindicators of such environmental contamination. The presence of Hg in the air within the Russian Federation is connected with its emission from local sources of anthropogenic and natural origin and also atmospheric transport from other areas of mercury contamination. To date, few studies report mercury distribution in the Crimean peninsula and the data are still fragmentary. The aim of this study was to use the lichens Evernia mesomorpha Nyl., E. prunastri (L.) Ach., Xanthoria parietina (L.) Th. Fr., Cladonia rangiformis Hoffm., and Parmelia sulcata Tayl., collected from various rural and urban regions of the Crimean peninsula, to assess Hg contamination. The sampling areas were located within central, southwestern, southern, southeastern and eastern regions of the Crimean peninsula (See Fig. 1 and Table) and included those characterized by the mercury ore deposits in the metallogenic zones of the southern Crimea foothills and coastal area and the Kerch peninsula as well as industrial activities (mining and quarrying) located within the Crimean peninsula (45°24N; 34°00'E). All measurements of Hg concentration in epiphytic lichens (n=60; samples collected between 2015 and 2018) were conducted using a model RA-915 atomic absorption spectrometer (Lumex, “Uranium Geology International Center”, Tomsk, Russia) with a PYRO-915 attachment. This instrument had been previously used with high efficiency for total mercury determination in lichens (Panichev N et al., 2019; Esbri JM et al., 2015). All data on Hg concentration in epiphytic lichens from different Crimean regions are summarized in Table and it was in the range of 0.037-0.306 mkg/g (See Fig. 2) with a median (Me) value of 0.070 mkg/g (p25=0.058 mkg/g, p75=0.089 mkg/g). In urban territories (n=34), median Hg concentration was found to be 0.067 mkg/g (p25=0.058 mkg/g, p75=0.086 mkg/g) and in natural ecosystems it was 0.084 mkg/g (p25=0.060 mkg/g, p75=0.100 mkg/g). It was found that epiphytic lichens from the protected and park areas in the southern region contain the highest Hg concentrations (р<0.01) compared to the central, eastern and southwestern regions (See Fig. 3). The results of Hg determination in lichens demonstrate higher Hg concentrations (р=0.003) in samples collected in Crimean foothills and mountains (500 to 1000 m above sea level) compared to the lowlands (See Fig. 4). The latter reflects the role of the Main Ridge of the Crimean mountains as a natural barrier for the Hg transported with air masses as well as natural sources and geochemical characteristics of the monitored areas (precipitation, marine aerosols, underwater volcanoes, geological deposits of Hg minerals). The obtained results do not point to significant signs of atmospheric air pollution with Hg using epiphytic lichens as bioindicators because Hg concentration in all analyzed samples was relatively low and comparable to background Hg concentrations in other regions of the Russian Federation and other CIS countries. Revealed variations are dependent on the ecosystem type and also could be explained by the geographical diversity of the Crimean peninsula. Although the present research suggests that most of Hg is derived from natural sources it can be hypothesized that Hg concentrations in the environment might be increasing in future as a result of human activity mainly through intensification of agriculture and industry in Crimea. The paper contains 4 Figures, 1 Table and 40 References.

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