EnvironmentalScienceProcesses & Impacts

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Use of moss and210

Technical University of Lodz, Institute of App

15, 90-924 Łodz, Poland. E-mail: mdlugosz

Tel: +48 42 631 31 67

† Student.

Cite this: DOI: 10.1039/c4em00366g

Received 1st July 2014Accepted 23rd September 2014

DOI: 10.1039/c4em00366g

rsc.li/process-impacts

This journal is © The Royal Society of

lichen species to identifyPo-contaminated regions

Magdalena Długosz-Lisiecka and Justyna Wrobel†

210Po concentration in urban air fluctuates as a result of natural 222Rn radionuclide exhalation and technical

activity that is especially linked with high-temperature processes. Each year, an average 11 GBq of 210Po is

released from local power plants into urban air. Over twomonths, about 180 samples in central Polandwere

collected. To detect the concentration of 210Po activity, two common species of biomonitors were chosen:

the moss Pleurozium schreberi and the lichen Hypogymnia physodes. For the same locale, 210Po in lichen

shows an average of twice the amount of activity concentration than the moss. In moss, 210Po

concentrations in Lodz ranged from 41.5 Bq kg�1 to 258.0 Bq kg�1, while in lichen it ranges from 74.2 Bq

kg�1 to 670.9 Bq kg�1. On the basis of the measured activity of 210Po maps, radionuclide distribution has

been prepared. For areas identified with higher concentrations of 210Po, Quantum Gis has been applied.

Environmental impact

This study is a continuation of the investigation of 210Po emission to the atmosphere. To identify areas with elevated content of this radionuclide, one lichen andone moss species were chosen. Both types of organisms were used for contamination factor determination and mapping of regions with higher 210Poconcentration in urban air. 210Po concentration in the lichen Hypogymnia physodes is an average of twice higher than in the moss Pleurozium schreberi. Thepresented maps conrm higher local emission of pollutants enriched in 210Po radionuclide. All regions with higher 210Po activity concentration can be stronglylinked with the release of escaping y ash from local coal power plants and old-type domestic central heating systems, mostly used in lo buildings in the centralpart of Lodz city.

Introduction

Urban air contains a whole range of radioactive elements ofdifferent natural and articial origins. The dominant part of thenatural isotopes is from the radioactive series, mainly uranium,radium and thorium, which are transported to the atmosphereby the soil resuspension process or as a result of industrialactivity, especially high-temperature processes.1,2 Such tech-nical activities discharge radionuclides in the source region.One of the most volatile and radiotoxic elements is polonium.

Polonium has many radioactive isotopes, with 210Po amongthe most important and most lasting presented in the envi-ronment, with a half-life of 138.4 days. 210Po is a product of the238U decay series and is released into the atmosphere via thedecay of 222Rn, which is spontaneously diffused from the earth'ssurface into the atmosphere. It decays continuously to 210Pothrough various other short-lived and long-lived radionuclides.In urban air, 210Po activity concentration is also a result ofcommon energetic coal combustion processes in power plantsand domestic furnaces. As a result of combustion processes,

lied Radiation Chemistry, Wroblewskiego

@mitr.p.lodz.pl; Fax: +48 42 631 31 05;

Chemistry 2014

210Po creates volatile compounds and almost immediatelyadsorbs on ne particles (especially those below 1 mm), whichcan easily penetrate the atmosphere despite the use of multi-level extraction or de-dusting systems. Ash fractions of less than1 mm are particularly dangerous as respiratory fractions.Emitted exhaust gas and ne particles of y ashes generatenatural radionuclides an order of magnitude greater than fossilfuels or surface soil in central Poland. The average activityconcentration of 210Po in escaping y ash reported3 previouslywas 1700 Bq kg�1. In the Lodz agglomeration, as a result of coalcombustion processes, about 11 GBq of 210Po and 0.9 GBq of210Pb per year are released into the atmosphere from three localpower plants.

Lichens are symbiotic organisms composed of fungi (myco-bionts) and green algae or cyanobacteria. Lichens and mossesin obtain their nutrient supply directly from atmosphericdeposition; as a result, they are effective biomonitors of envi-ronmental contamination. Both of them, thanks to theirmorphological and physiological features, show a high ability toaccumulate air pollutants (including toxic pollutants) and 210Poas well. In Poland, the most widespread and highly tolerant ofcontamination are these two organisms: the moss Pleuroziumschreberi and lichen Hypogymnia physodes. However, lichen aremore sensitive to SO2 and other pollutants; as a result, it is notpossible to correctly monitor 210Po in regions of high

Environ. Sci.: Processes Impacts

Environmental Science: Processes & Impacts Paper

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contamination, named “lichen deserts.” In general, both bio-monitors occur as a ratio of the activity concentration of 210Poand other radionuclides in a one-gram mass of the dryorganism and activity in the urban air.1,2 This feature helps toidentify the source of 210Po emission.

Mosses and lichen have been widely used as bio-accumulation,4 absorption,5 localization,6 release,7 and toxicityindicators of metals8 and radionuclides9 in the atmosphere andare measured by various instrumental techniques.10 210Po activitymonitoring by use of lichen andmosses was applied previously inTurkey,1,2,11 Sweden,12 India,13 Syria14 and in Poland.15

The aim of this work is to identify regions of higher 210Poconcentration in the urban air of the Lodzian agglomerationaer a heating period. Therefore, in addition to the standardalpha-spectrometric analysis, powerful visualization tools, suchas the Qantum Gis application,16 have been applied.

Table 2 Activity concentration in lichen andmosses in forests near thesmall villages of Witow and Jamno

210Po activity concentration [Bq kg�1]

Materials and methodsSampling

Lodz city is one of the most densely populated Polish andEuropean cities. Samples were taken in the Lodzian agglomer-ation, consisting of Lodz and surrounding towns and thevillages of Witow, Zawoja and Jamno. There are huge environ-mental contrasts between these regions. Most samples weretaken in Lodz city located in central Poland. In the city centrum,three coal power plants are located with a total power of 2.6 GW.For comparison, samples were taken in regions surrounding thetowns and villages.

About 180 lichen and moss samples were collected. Sampleswere taken out in February and March 2014, just aer the coldwinter season. The samples were taken only from trees, not fromconcrete or metal elements, for a normalized living condition ofthe biomonitors. The samples were dried at room temperaturefor 3 days minimum, and aer this the lichen thallus and mossleaves were cleaned, fragmented and ground in a mortar. Anaverage of 0.2 g of the green part of the leaves of the moss andtop part of the lichen thallus samples were placed in a Teoncontainer and lled with 50 ml of 1 M HCl. Aer 24 hours ofleaching, the solution was ltered. 210Po present in the solutionwas separated by spontaneous deposition on silver discs at 80 �Cover a minimum of 8 h. The activity of 210Po was determinedusing an alpha spectrometry system with a PIPS detector.

Witow village Jamno village

Pleurozium schreberi 91.6 � 6.2 69.8 � 4.5Polytrichum commune 154 � 8 144 � 7Hypogymnia physodes 273 � 9 205 � 8Cladina rangiferina 164 � 8 No data

Accuracy

The yield of polonium separation by this method was calculatedby use of IAEA reference materials IAEA 300 and IAEA 434.Results are presented in Table 1.

Table 1 The 210Po measured and certified activity in reference materials

Code 210Po measured activity [Bq kg�1]

IAEA 300 marine sediment 340 � 18IAEA 434 phosphogypsum 641 � 23

Environ. Sci.: Processes Impacts

Evidently, good agreement between the measured andcertied value of activity was obtained.

Results and discussionThe choice of moss and lichen species for analysis

In the forest located next to the village of Witow, several speciesof mosses and lichens (mosses: Pleurozium schreberi, Poly-trichum commune, lichens: Hypogymnia physodes, Cladina ran-giferina (L.) Nyl.) were collected to compare the 210Po activityconcentration in different species. Polytrichum commune accu-mulated more 210Po (�154 Bq kg�1) than Pleurozium schreberi(<100 Bq kg�1). The lichens also show certain trends. Hypo-gymnia physodes had an accumulated 273 Bq kg�1, while Cla-dina rangiferina had 164 Bq kg�1 at the Witow region.

In a forest located close to Jamno village, results showed thesame trend, which conrms the accumulation ability of variousindicator species Table 2.

For further analysis of 210Po, the commonly occurring mossPleurozium schreberi and lichen Hypogymnia physodes wereselected. The relatively higher 210Po activity concentration inbiomonitor samples is typical in regions of polonium emis-sion.1,2,11,17 In regions with higher source emission (the center ofLodz), the ratio of activity of 210Po in samples of lichen relativeto the activity in mosses at the same location ranged from 0.92to 3, with an average ratio equal to 1.99 (Fig. 1). Fig. 1 conrms aweak correlation (r ¼ 0.73) between 210Po activity concentrationin lichen and moss samples at the same location. Therefore,lichen, as the better accumulator of this metal, is more usefulfor monitoring the activity of 210Po in urban air.

Difference of 210Po activity in various parts of the biomonitors'body

To understand the absorption mechanism, the radionuclidewas analyzed separately in different parts of the biomonitor. Inthis study, statistically signicant differences between 210Poactivity concentration in various parts of the moss body and indifferent sizes of lichen thalli were found.

210Po certied activity [Bq kg�1] Standard deviation%

340.5 �0.1680.0 (on the base of 210Pb) 5.6

This journal is © The Royal Society of Chemistry 2014

Fig. 1 The 210Po activity concentration in lichen Hypogymnia phys-odes and in moss Pleurozium schreberi at the same sampling site.

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Lichen shows an intercellular absorption of the metals18

through an exchange process, thus lichens are perfect accu-mulators of the metals. Because they have no root system,lichen can uptake metals from the atmosphere and then effi-ciently transport it through the whole thallus. Local insolationand the presence of SO2 and other stress compounds candramatically change the rate of growth and reduce the lichenpopulation.

On the other hand, a large lichen thallus seems to be anefficient tool for the absorption of pollutants by wet and dryprecipitation from the atmosphere. For Hypogymnia physodes,small and large samples from the same location were analyzed.The same species can exhibit differences in theiraccumulation properties depending on the samples' diameter.A brancher thallus of the lichen body can accumulate, onaverage, 50% more polonium than a small part of the lichenbody (Table 3).

Mosses do not have an epidermis and cuticle; thereforemetal ions can easily penetrate the cell wall. Mosses do not havea proper root system, but have threadlike rhizoids only as ananchor to the substrate. Mosses absorb water and nutrientsmainly through their leaves. It is well known that the transportof minerals between segments and parts of the moss body islimited because of the lack of vascular tissue. Mosses accumu-late metals in a passive ion exchange.18 In this study, signicantdifference (t-test, p < 0.005) in 210Po activity concentrationbetween the three moss body parts was measured. Theconcentration of 210Po in the pincer system is several timeshigher than in stems and leaves. Similar results were noted forthe root system of the orchid Cymbidium aloifolium (Lo)Swartz.19 The main reason for the higher concentration of 210Po

Table 3 210Po activity concentration in relation to size of lichenHypogymnia physodes

Code sample Small thallus [Bq kg�1] Large thallus [Bq kg�1]

10 121 � 5 203 � 1012 168 � 7 244 � 7Z4 153 � 6 471 � 16

This journal is © The Royal Society of Chemistry 2014

in the different parts of the plant might be the articiallyproduced fallout radionuclides from the past. It should benoted that 210Po activity in the surface soil is an order ofmagnitude lower. The average activity of 210Po in the topsoil isequal to 29.1 � 1.5 Bq kg�1. Polonium content in soil could notbe a reason for a higher radionuclide activity concentration inthe pincer system of the analysed Pleurozium schreberi speciespresented in Table 4. This data conrms the absorption ofradionuclide directly from the atmosphere by dry and wetprecipitation of the pollutants. Escaped y ashes released fromtechnical activities seem to be the main source of the highest210Po activity concentration measured in the biomonitors in theLodzian agglomeration.

Inuence of wind on 210Po distribution

The distribution of 210Po activity concentration in biomonitorsdepends on 210Pb and the articial discharge of pollutants fromdomestic heating systems or local coal power plants20 enhancedin 210Pb and 210Po radionuclides. The samples were taken justaer the snow layer disappeared, in a period of low natural210Pb production from 222Rn radionuclide exhalated from theground and maximal 210Pb and 210Po emission from energeticcoal combustion. The wind rose for Lodz suggests north-westand west, and rarely, an east direction of the wind. In conclu-sion, most contaminations emitted mostly from point sourcesare preferably moved in these directions Fig. 2.

The analysis conrmed the correlation between the 210Poactivity concentration in mosses and lichens depending on thedistance from the emission source. In this study, several regionswere found with a higher 210Po activity concentration. Thelocalization of each suggests energetic coal combustion as thedominant 210Po origin. For easy indication21 of such regions, acontamination factor, Fp for moss or Fh for lichen, has beenapplied:

Fp ¼ Axp

ATxp

and Fh ¼ Axh

ATxh

(1)

where: Ax is210Po activity concentration in samples of Pleu-

rozium schreberi (p) orHypogymnia physodes (h), taken in the citycentre, and ATx is

210Po activity concentration in samples of bothbiomonitors (p) and (h), sampled in the forest, far (about 10 km)from anthropogenic activity.

The contamination factor Fp for Pleurozium schreberi mossuctuates from 1.07 to 8.78, with an average of 2.45. ForHypogymnia physodes lichen, Fh value was obtained between0.95 and 9.06, with an average of 3.00.

Table 4 210Po activity in various moss Pleurozium schreberi bodyparts

Code sample Pincers [Bq kg�1] Stems [Bq kg�1] Leaves [Bq kg�1]

W4 786 � 16 415 � 12 125 � 8J1 737 � 19 373 � 10 69.8 � 3.5J2 847 � 28 226 � 9 144 � 6

Environ. Sci.: Processes Impacts

Fig. 2 Wind rose for (a) Lodz city centrum and (b) suburb area.

Fig. 3 Contamination factors for (a) Hypogymnia physodes and (b)Pleurozium schreberi vs. distance from the coal power plant stack.

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The contamination factor for both biomonitors uctuateswith distance from the power plant stack. Depending on thewind, the maximum rose of 210Po activity concentration wasobtained for a distance of about one km, which then decreases.Because of the presence of lichen in the desert, it was notpossible to verify 210Po presence in all directions around thelocal power plants (Fig. 3). For better visualization of the 210Pocontent in the air, easy maps were prepared.

Fig. 4 Map of Fp in lichen (Pleurozium schreberi) in the Lodzianagglomeration.

Maps of 210Po activity concentration in the Lodzianagglomeration

Both biomonitors show maximal concentrations in regions ofcoal power plants that are located close to large urban settle-ments and in the region of old Town (Fig. 4 and 5). In thisregion, contamination factors Fp and Fh were equal to 9.1(activity concentration equal 671 � 23 Bq kg�1) and 8.8 (457 �21 Bq kg�1), respectively. A lower activity concentration was

Environ. Sci.: Processes Impacts

determined in the suburb of Lodz city. In this region, maximalcontamination factors Fp and Fh produced values of 5.1 (379 �15 Bq kg�1) and 1.7 (112 � 4 Bq kg�1), respectively. The lowestactivity concentration was measured from samples taken outfrom deep forests located next to small villages. These resultswere applied as a natural background of 210Po content in thebiomonitors.

In this study, signicant differences in concentrations in thepower plant region and the suburb were observed (t-test, p <0.001). In the suburb region, the activity of 210Po is lower thanthe uctuations between radionuclide concentrations. Theactivity in the biomonitors at the sampling points could be

This journal is © The Royal Society of Chemistry 2014

Fig. 5 Map of Fh in the moss (Hypogymnia physodes) in the Lodzianagglomeration.

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affected by various ecological conditions and individual lichenand moss predispositions. The uncertainty of the presentedresults does not exceed 5%. The presented maps (Fig. 4 and 5)suggest the presence of local pollution emission sources. Theprevailing winds inuence the local distribution of ne,escaping y ashes and the dilution of 210Po activityconcentration.

Both maps were elaborated in the Quantum Gis application,version 1.8.0 (Lisboa). For visualization, three layers wereapplied: a map of the city, map of the sampling points, andinterpolation results. The calculated 210Po contaminationfactors were visualized by interpolation methods based onInverse Distance Weighting (IDW).

In the next step of this study, correlation between 210Po andother natural as well as articial radionuclides will be analyzed.

Conclusion

This study is a continuation of the investigation on 210Poemission to the atmosphere.22 Biomonitors were used to iden-tify areas with elevated content of this radionuclide and thus thelocal sources of its emission. For 210Po activity concentrationanalysis, one lichen and one moss species were chosen. Bothtypes of organisms were applied for contamination factordetermination and mapping of regions with higher 210Poactivity concentration in urban air.

210Po concentration in the lichen Hypogymnia physodes is anaverage of twice higher than in the moss Pleurozium schreberi.However, Hypogymnia physodes, as a more suitable biomonitor,could not be found in the most polluted regions; therefore thehighest 210Po concentration could not be analyzed.

The presented maps conrm higher local emission ofpollutants enriched in 210Po radionuclide. All regions identiedwith higher 210Po contamination can be strongly linked with therelease of escaping y ashes from the local coal power plantsand old-type domestic central heating systems mostly used inlo buildings in the central part of Lodz city.

Acknowledgements

This research work is supported by the National Science Centrein the grant SONATA no. UMO-2012/07/D/ST10/02874.

This journal is © The Royal Society of Chemistry 2014

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