Lichens as Biomonitors of Air Pollutants Deposition: Strategically Important Element Pollution 


 In this study, different lichen species (Lobaria pulmonaria, Cladonia furcata, Usnea longissima, Xanthoparmelia somloensis, and Flavopormelia caperata) as biomonitors of air pollutants deposition were investigated and element pollution (Ta, Bi, Hf, Nb, Ga, Sc, Li, Y, Ce, and Sr) was evaluated. According to obtained data, the highest accumulation was 43.9±2.1 mg/kg in Xanthoparmelia somloensis. Sr value detected in each lichen was quite high. Sr percentages for Lobaria pulmonaria, Cladonia furcata, Usnea longissima, Xanthoparmelia somloensis, and Flavopormelia caperata were 77%, 66%, 87%, 58%, and 78%, respectively. This indicates that the lichens accumulate Sr well. Also, other strategically important elements were also accumulative by lichens. The highest contamination factor (CF) values in lichen species were determined for Sr and Ta. The highest CF values of Hf, Nb, Li, Ga, and Bi were calculated for L. pulmonaria while the highest CF values of Sr, Y, Sc, and Ce were calculated for Xanthoparmelia somloensis. Moreover, the highest CF value of Ta was calculated for Flavopormelia caperata. EF values for Lobaria pulmonaria, Cladonia furcata, and Flavopormelia caperata were >10, only for Bi. EF values for Usnea longissima were <10. EF values for Xanthoparmelia somloensis were >10. PLI values for Lobaria pulmonaria and Usnea longissima were >1. As a result, the presence of strategically important elements detected in lichen species showed that lichens can be used as biomonitors of air pollutants.


Introduction
Environmental pollution is one of the major issues threatening human health and the ecosystem because of its toxicity and harmful effect.The major factors that contributed to the pollution of the environment are anthropogenic activities, the industrial revolution, and rapid development (Wang and Zhao, 2016;Maslamani et al., 2021).Nowadays, one of the main leading global problems is the presence of various pollutants in the environment.They not only affect the health of humans but also overshadow the life of other creatures (Bagheri et al., 2021).Chemical pollution of the environment which is one of the pollutions has major impacts on biodiversity, ecosystem function, and services throughout the world (Rockström et al., 2009;Kean et al., 2021).
The strategically important elements have various usage fields.As a result of the wide usage of these elements, they are released to the environment.Therefore, these elements have both pollutant characteristics and strategically importance.The elements having these properties chosen in this study are hafnium (Hf), tantalum (Ta), niobium (Nb), lithium (Li), strontium (Sr), bismuth (Bi), yttrium (Y), cerium (Ce), scandium (Sc), and gallium (Ga).
Gallium is an element with no known biological functions in livings (Kircheva and Dudev, 2021).Gallium has been extensively used in semiconductor industry.Gallium arsenide is applied in various electronic components.Furthermore, gallium has been extensively used in the medicine (Asadian and Ahmadi, 2020) because of its immunomodulating, antiinflammatory, analgesic, and anti-hypercalcemic activities (Kircheva and Dudev, 2021).
Bismuth is a green and rarely heavy metal.It has good chemical stability and peculiar physical and chemical properties (Wen et al., 2021).The development in the field of communication and microelectronics has been reflected in a concomitant increase in the demand for strategic metals tantalum (Ta) and niobium (Nb) (Shikika et al., 2020).Lithium (Li) has strategic importance for numerous industrial applications (e.g.lithium-ion batteries for mobile devices and electric vehicles) (WEF, 2019;Millot and Négrel, 2021).Hafnium (Hf) is a typical reactive element.Therefore, there is the high level of interest in using Hf in nickel-based alloy systems (Yancheshmeh et al., 2018).Strontium (Sr) is an alkaline-earth metal that is a common trace element in the environment.It has commercial uses (e.g.glass, ceramics, and ferrite magnets).Strontium consumption via various ways can have adverse health effects (e.g.osteomalacia and abnormal bone development (Musgrove, 2021).Yttrium is used in magnetic garnets (Yang et al., 2021).It has the effect of refining the grains of magnesium alloys, can reduce the amount of calcium required in magnesium-based alloys and may improve the properties of the alloy as well (Cheng et al., 2021).The high content of rare earth element yttrium in various products results in the accumulation in the body through the food chain, and endanger the health by inhibiting the growth of pre-osteoblasts and poisoning the nervous system (Gonzalez et al., 2015;Liu et al., 2021).Cerium (Ce) is the most abundant rare earth metal found in the earth's crust (Kurian, 2020).The long-term ingestion of rare earth elements influences on activities of digestive enzymes (Zhu et al.;2005;Migaszewski and Galuszka, 2014).Cerium minerals have been processed for industrial applications (Kurian, 2020).Scandium (Sc) is one of the most valuable metals.Amongst many applications, it is used in the production of high strength and lightweight aluminium alloys and solid oxide fuel cells (Peters et al., 2020).
The amount of the elements accumulated in the lichen thallus proportionally represents their presence in the atmosphere.When it comes to epiphytic species, the thallus acts as a vehicle for transmitting the particles by direct deposition from the air.Therefore, lichens serve as valid instruments and proxies to assess the air quality and the potential contamination sources of elements (Conti and Cecchetti, 2001;Brunialti and Frati, 2014;Parviainen et al., 2020).Their prolonged exposure time to environmental factors, lack of cuticles or stomata and the absence of mechanisms of excretion make lichens behave like bioaccumulators of aerosol (Hale, 1979;1983;Parviainen et al., 2020).Lichens can accumulate even minor elements to measurable concentrations (Gauslaa et al., 2020).
The main purpose of this study is to determine the accumulation of some strategically important elements (Ta, Bi, Hf, Nb, Ga, Sc, Li, Y, Ce, and Sr) in different lichen species (Lobaria pulmonaria, Cladonia furcata, Usnea longissima, Xanthoparmelia somloensis, and Flavopormelia caperata).When the literature is examined, there are few studies on accumulation of strategically important elements in lichens, and therefore we focused on the following issues in our study; (i) In the study, we identified different lichen species (Lobaria pulmonaria, Cladonia furcata, Usnea longissima, Xanthoparmelia somloensis, and Flavopormelia caperata) in Artvin, Murgul (Turkey) and determined the strategically important elements in each lichen species (ii) We statistically evaluated the relationship between lichens in terms of strategic elements accumulated by lichens (iii) We calculated the accumulation amounts and percentages of the strategic elements in lichen species (iv) We assessed the element pollution by calculating enrichment factors, contamination factors, and pollution loud indexes.Therefore, this study is quite new, original, and a study that will make a sound in the literature.
Lichen samples are harvested by hand with an instrument.Lichen samples are brought to the laboratory.Lichens are removed from foreign materials.Then, lichen samples are dried at 25 o C and powdered.The analysis procedure for lichen samples are briefly given: samples are cold leached with HNO3.After cooling a modified Aqua Regia solution of equal parts concentrated HCl, HNO3 and DI H2O are added to each sample to leach in a heating block of the hot water bath.Samples are made up to volume with dilute HCl before filtered.All samples are analyzed by ICP/MS (ICP/MS-Perkin-Elmer ELAN 9000) to evaluate strategic elements (Hf, Ta, Nb, Li, Sr, Bi, Y, Sc, Ce, and Ga).Details of QA/AC are given in Table S1.

Pollution status
The terrigenous or anthropogenic origin of elements in lichens were evaluated by the calculated enrichment factor (EF) (Parviainen et al., 2020).Enrichment factors for different lichen species were calculated by: where EF: enrichment factor, Elichen: element value in lichen (mg/kg), Allichen: Al value in lichen (mg/kg), Ecrust: element value in the Earth's crust (mg/kg) Alcrust: Al value in the Earth's crust (mg/kg).
The degree of contamination in Artvin (Murgul) region were evaluated by the calculated contamination factor (CF) (Koroleva and Revunkov, 2017).Contamination factors were calculated by: where CF: contamination factor, Ci: element value in lichen (mg/kg), Cb: element value in control area (mg/kg).In this study, eastern Alps and northern Apennines were chosen as control (Cecconi et al., 2018) (for all elements, except elements Ta and Ga which do not exist in their study).Ta and Ga values were taken from Markert (1991).
Pollution load index (PLI) indicating how much the sample exceeds the metal concentrations of natural environments and also giving an indication of the overall toxicity status for the sample is defined as the nth root of the multiplication of CFs (Salo et al., 2012).PLI was calculated by: where,  1 is the CF of the first element,  2 is the CF of the second element value,  3 is the CF of the third element value,   is the CF of the nth element in the lichens species.

Statistical analysis
IBM SPSS Statistics 22 (USA) is used to evaluate data.Pearson correlation tested to indicate the relationship between lichens that accumulate strategic elements.In addition, the relationship between strategic elements detected in lichens was examined.

Accumulation by Lobaria pulmonaria
Strategically important elements accumulated by Lobaria pulmonaria are given in Figure 1.lugubris.In our study, the lowest element concentration was 0.006±0.001mg/kg for Ta.

Accumulation by Usnea longissima
Strategically important elements accumulated by Usnea longissima are given in Figure 3.
It can be said that the best accumulation by Xanthoparmelia somloensis is for Sr.The distribution percentages of the strategic elements accumulated by Xanthoparmelia somloensis are given in Figure 4(b).According to Figure 4(b), the highest element value was 58% for Sr, while the lowest element value 0.0026% for Ta.Also, Bi and Nb values in Xanthoparmelia somloensis were below 1%.Y, Sc, Ce, Ga, and Li values were 7%, 5%, 21%, 4%, and 5%, respectively.

Accumulation by Flavopormelia caperata
Strategically important elements accumulated by Flavopormelia caperata are given in Figure 5. the highest element value was 78% for Sr, while the lowest element value 0.0089% for Ta.

Comparison of strategic elements accumulated by lichen species
Comparison of strategically important elements accumulated by Lobaria pulmonaria, Cladonia furcata, Usnea longissima, Xanthoparmelia somloensis, and Flavopormelia caperata is given in Figure 6.

Assessment of pollution status
In this study, after the accumulation values of strategically important elements in different lichen species were determined, pollution status values were calculated.In this context, the enrichment factors calculated for different lichen species are given in Table 1.(Bi:31.65,Y:12.46,Sc:12.93,and Ce:12.25).
The contamination factors are given in Figure S1.As a result, the highest CF values in lichen species investigated were determined for Sr and Ta.Biological behaviours of Sr resemble those of calcium because of chemical similarity of them.The close relationship between calcium and strontium has been proven in studies with various plant systems, algae and yeasts.It has been shown that strontium may substitute for calcium in binding processes at biological cell surfaces as well as in active uptake via divalent cation transport systems (Anupama et al., 2016).Therefore, it is not surprising the high value of Sr in lichen species.Although strontium is released into the atmosphere as a result of natural processes such as entrainment of dust particles, resuspension of soil by wind, and sea spray (URL, 1), antropogenic sources are also present.Near to the studied region, the copper flotation wastes from a mine are stored in the empty pit mine, the ore of which is finished.It is known that high concentrations of strontium are detected in drinking water in the area close to where these wastes are stored.Strontium is probably dispersed by atmospheric transport to near region of these flotation waste deposits and is subsequently deposited in lichens.The transportation and redeposition on Earth by dry or wet deposition of Sr released into the air from various activities is reported by WHO (2010).Rain, sleet, snow, or other forms of moisture can wash airborne particles containing Sr from the atmosphere by the process of wet deposition (URL, 1).Strontium identification in air from the hazardous waste sites was reported in the literature (URL, 1).Furthermore, as reported by (URL, 1) human activities releasing strontium into the atmosphere include burning of coal, and land application of phosphate fertilizers resulting in the release into the atmosphere in windblown soil.The main sources of tantalum in the environment are geologic, mostly as a result of the weathering of rocks, but a potential anthropogenic source of it is from the combustion of coal (Divine and Goering, 2004;Goering and Ziegler, 2004

Statistics studies
The relationships between lichens that accumulate strategic elements were given in Table 2.

Figure 6 .
Figure 6.Here There are six categories corresponding to CF values(Stojanowska et al., 2020): Category 1 (C1) CF < 1 no contamination; Category 2 (C2) 1 < CF < 2 suspected contamination; Category 3 (C3) 2 < CF < 3.5 slight contamination; Category 4 (C4) 3.5 < CF < 8 moderate contamination; Category 5 (C5) 8 < CF < 27 severe contamination; Category 6 (C6) CF > 27 extreme contamination.The highest CF value was determined for Ta (C4) in Lobaria pulmonaria while Nb (C4), Ga (C4), and Li (C4) followed it.These results indicated moderate contamination.The elements that indicated slight contamination were Ce (C3) and Sc (C3) while Y (C2), Bi (C2), and Sr (C2) indicated suspected contamination.Hf (C1) indicated no contamination.CFs were calculated at the C4 category for three elements, C3 category for two elements, C2 category for three elements, and C1 category for one element.The highest CF value was determined for Sr (C5) in Cladonia furcata indicating severe contamination.As a result, it can be said that the source of Sr in the lichen Cladonia furcata is probably anthropogenic emissions.Ce and Y were at C2 category indicating suspected contamination.Sc (C1), Li (C1), Ga (C1), Bi (C1), Hf (C1), Nb (C1), and Ta (C1) indicated no contamination.CFs were calculated at the C1 category for seven elements, C2 category for two elements, and C5 category for one element.Most of the CFs were classified as C1.The highest CF value was determined for Ta (C4) in Usnea longissima indicating moderate contamination.Sr, Ce, Ga, Sc and Nb were at C2 category indicating suspected contamination.Li (C1), Y (C1), Hf (C1), and Bi (C1) indicated no contamination.CFs were calculated at the C1 category for four elements, C2 category for five elements, and C4 category for one element.The highest CF value was determined for Sr (C5) in Xanthoparmelia somloensis while and Ce (C5) followed it.These results indicated severe contamination.Y and Li were at C4 category indicating moderate contamination.Sc and Ga were at C3 category indicating slight contamination.Nb (C1), Hf (C1), Bi (C1), and Ta (C1) indicated no contamination.CFs were calculated at the C5, C4, and C3 categories for two elements, C1 category for one element.As a result, it can be said that the source of Sr and Ce in the lichen Xanthoparmelia somloensis is probably anthropogenic emissions.The highest CF value was determined for Ta (C5) in Flavopormelia caperata indicating severe contamination.As a result, it can be said that the source of Ta in the lichen Flavopormelia caperata is probably anthropogenic emissions.Sr was at C2 category indicating suspected contamination.Nb (C1), Ga (C1), Sc (C1), Bi (C1), Ce (C1), Li (C1), Y (C1), and Hf (C1) indicated no contamination.CFs were calculated at the C1 category for eight elements, C5 and C2 category for one element.Most of the CFs were classified as C1.
Considering these values, it can be said that the best accumulation by Lobaria pulmonaria is for Sr.The distribution percentages of the strategic Rivera et al. (2018)reported Ta concentration as 0.00275 µg/g in lichen Himantormia lugubris.In our study, Hf, Bi, Nb, Ga, Y, Sc, Li, and Ce concentrations in Lobaria pulmonaria were 0.031±0.001,0.04±0.002,0.12±0.006,0.4±0.02,0.657±0.03,0.7±0.03,0.81±0.04,and2.2±0.1 mg/kg, respectively.Rivera et al. (2018)reported Hf and Sc concentrations as 0.0377 and 0.319 µg/g in lichen Himantormia lugubris, respectively.In our Rivera et al. (2018)entration was 26.8±1.3mg/kgforSr,while the lowest element concentration was 0.006±0.001mg/kgforTa.In the literature,Rivera et al. (2018)reported Sr and Ta concentrations between 17 and 63 µg/g and between <0.002 and 0.0044 µg/g in lichen Usnea antarctica, respectively.Furthermore, the highest Sr and Ta In the literature,Rivera et al. (2018)reported Hf and Sc concentrations between 0.0088 and 0.0447 µg/g and between 0.158 and 1.051 µg/g in lichen Usnea antarctica, respectively.Furthermore, the highest Hf and Sc concentrations in Usnea aurantiacoatra were reported as 0.0278 µg/g and 0.576 µg/g, respectively.In our study, the strategic elements in Usnea longissima were Sr>Ce>Y>Sc>Li>Ga>Nb>Hf>Bi>Ta.It can be said that the best accumulation by Usnea longissima is for Sr.The distribution percentages of the strategic elements accumulated by Usnea longissima are given in Figure3(b).According to Figure3(b), the highest element value was 87% for Sr, while the lowest element value 0.027% for Ta.Also, Bi, Nb, and Hf values in Usnea longissima were below 1%.Y, Sc, Ce, Ga, and Li values were 2%, 2%, 7%, 1%, and 1%, respectively.

Table 1 .
(Parviainen et al., 2020)ed, the highest EF value in Lobaria pulmonaria was 15.83 for Bi, while the lowest value was 0.27 for Hf.The highest EF value in Cladonia furcata was 23.74 for Bi, while the lowest value was 0.30 for Ta.The highest EF value in Usnea longissima was 7.91 for Bi, while the lowest value was 0.17 for Nb.The highest EF value in Xanthoparmelia somloensis was 31.65 for Bi, while the lowest value was 0.10 for Ta.The highest EF value in Flavopormelia caperata was 31.65 for Bi, while the lowest value was 0.20 for Ta.EF values < 10 are considered as terrigenous, whereas EF values > 10 are considered to be impacted by anthropogenic activity(Parviainen et al., 2020).According to Table1, EF values for Lobaria pulmonaria, Cladonia furcata, and Flavopormelia caperata were >10, only for Bi.EF values for Usnea longissima were <10.EF values for Xanthoparmelia somloensis were >10 ; URL, 2).As a result of combustion of coal may caused high Ta in lichens investigated.The highest CF values of Hf, Nb, Li, Ga, and Bi were calculated for L. pulmonaria while the highest CF values of Sr, Y, Sc, and Ce were calculated for Xanthoparmelia somloensis.Moreover, the highest CF value of Ta was calculated for Flavopormelia caperata.In this study, pollution loud index (PLI) values were calculated within the scope of this study.A PLI below 1 indicates that elemental loads are near the background level, and above 1 indicate the extent of pollution.PLI indicates how much a sample exceeds the metal concentrations of natural environments and give an indication of the overall toxicity status for a sample (Salo et al., 2012).According to obtained data, PLI values for Lobaria pulmonaria and Usnea longissima were >1.PLI values for Lobaria pulmonaria and Usnea longissima were 2.43 and 1.14, respectively.PLI values for Cladonia furcata, Xanthoparmelia somloensis, and Flavopormelia caperata were 0.19, 0.89, and 0.57, respectively.