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Geothermal Resources Council Transactions, Vol. 21, SeptembedOctober 1997

Monitoring of Arsenic, Boron and Mercury by Lichen and Soil Analysis in the Mt. Amiata Geothermal Area (Central )*

Stefan0 Loppi, Dipartimento di Biologia Ambientale UniversitP di Via P.A. Mattioli 4,l-53100Siena, Italy

ABSTRACT Epiphytic lichens and top-soils fiom the Mt. Amiata geo- ingly used as biomonitors. In forest ecosystems, plant leaves thermal field (central Italy) were analyzed for their As, B and are the main interceptor of airborne elements, however element Hg content. Three areas were selected: 1) Abbadia S. Salvatore, uptake via the roots may confbse and obscure the interpretation where a large Hg mine with smelting and roasting plant was lo- of leaf data in terms of airborne deposition (Deu and Kreeb, cated; 2) , where there are geothermal power 1993). Lichens, symbiotic organisms consisting of algae and plants; 3) a remote site far from mines and geothermal power fungi, do not depend on root uptake and receive nutrients di- plants. The results showed that the geothermal power plants do rectly from the atmosphere. They lack a waxy cuticle and sto- not represent a macroscopic source of arsenic and boron con- mata, and the elements are easily incorporated in their tissues tamination in the area. As far as mercury is concerned, at the Hg (Hale, 1983). Furthermore, the element content of lichen thalli mining area of Abbadia S. Salvatore concentrations were ex- has been found to be directly correlated with environmental tremely high both in soil and epiphytic lichens, and the anoma- levels (Sloof & Wolterbeek, 1991). Lichens that grow on trees lous content in these organisms was due to the uptake of ele- (epiphytic) have proved to be very useful for monitoring the mental mercury originating from soil degassing. At the geo- pollution load arising from geothermal power plants (Loppi, thermal area of Piancastagnaio, soil mercury was not different 1996; Loppi and Bargagli, 1996). from that in the control area, but Hg in lichens was almost twice The aim of the present study, performed in the Mt. Amiata the control levels, suggesting that the gaseous emissions from geothermal area, was to evaluate the amount of As, B and Hg the geothermal power plants are an important source of air con- present-due to the exploitation of geothermal fluids, by assay- tamination. ing epiphytic lichens and top-soil. To achieve this goal, three areas were selected: 1) Abbadia S. Salvatore, where a large Hg mine with smelting and roasting plant was located; 2) Pian- Introduction castagnaio, where there are geothermal power plants; 3) a re- Although geothermal energy was regarded as a clean re- mote site far from mines and geothermal power plants. source until the 1960s, it is by no means without environmental impact (hannsson & Kristmannsdbttir 1992). Trace ele- ments such as As, B and Hg are commonly associated with geo- Study Area thermal fluids, their relative concentrations depending on fluid Mt. Amiata (1738 m) in southern (central Italy), characteristics (Bowen, 1989). Biological hazard due to geo- was once well known for its cinnabar deposits. Total produc- thermal emissions has mainly been investigated in terms of tion of Hg output from mines exceeded 3010~flasks (Bombace mercury (Siegel and Siegel, 1975). et al., 1973). Mining and smelting activities ceased in 1976, but Biological monitoring has proved to be very useful in the as- high levels of Hg are still present in soil, air and vegetation sessment of air pollution and different plant species are increas- (Barghigiani and Ristori, 1994). The geothermal field extends over an area of about 80 km2

*Research carried out in the framework of Contract N. 10/94 with ENEL with elevation ranging from 350 to 1000 m. The geological set- SPA. ting consists of sedimentary (up to 700-800 m) and volcanic

137 Loppi

(above 800 m) rocks. The climate is humid sub Mediterranean, means was tested by one-way analysis of variance (ANOVA) with mean annual rainfall in the range of 1000-1555 mm and using the Scheffe’s test. mean annual temperatures ranging from 9.7 to 1 1.3”C. Four power plants are in operation in the area. Three of them Results and Discussion (PC3, PC4, Bellavista) have a nominal power of 20 MW with condensing turbine, and use fluids from the deep reservoir Table 2 summarizes the results of lichen and soil analyses at (about 3500 m). The other power plant (PC2) is non- the three locations. With respect to the control area, only con- condensing with a nominal power of 8 MW; the fluids ex- centrations of Hg turned out to be higher in lichens at Abbadia ploited are from the shallow reservoir (about 800 m). All of S. Salvatore and Piancastagnaio and only at Abbadia S. Salva- them re-inject the exploited fluids as a means of waste disposal. tore in soil. Table 1 reports the main features of the power plants in terms of airborne pollutants emitted (ENEL,1996). Table 2. Mean values 2 standard deviation and ranges of concentrations @g/gdw) of As, B and Hg in lichen and soil samples. Different letters indi- Table 1. Main features of the geothermal power plants in terms of air- cate differences at p 0.05. borne pollutants emitted (from ENEL, 1996). As B Hg, Abbadia S. Salvatore (mining area)

Lichen 2.88 -C 0.34 9.9 2 3.6 1.27 -t 1.49 (2.57 - 3.43) (5.4 - 13.8) (0.2 - 3.87)

Soil 21.6 -c 6.9 40.5 2 22.2 28.80 -c 19.48“ (13.9 - 30.7) (24 - 79.5) (6.07 - 59.74)

Materials and Methods Piancastagnaio (geothermal area) In May 1995, in each of the three areas selected, 3-6 whole Lichen 12.58 & 0.46 113.1 -c 4.1 0.43 -t 0.1 6 Ii thalli of the foliose lichen Parmelia sulcata were collected in 5 sampling sites at a height of 1.5-2 m above the ground. This (2.02 - 3.28) (9.5 - 19.8) (0.27 - 0.69) species was chosen because of its wide distribution and be- Soil 14.95 +. 2.83 50.5 2 10.3 1.23 2 0.66 cause it had already been used in biomonitoring surveys in the (11.4 - 19.1 ) (33 - 60) (0.69 - 2.25) study area (Bargagli et al., 1987a). At each site, 8 superficial (0- 10 cm) soil samples were also taken. Remote Site (control area)

In the laboratory, lichen and soil samples were air dried and Lichen 2.82 2 0.68 10.1 2 1.9 0.23 2 0.1 t: sorted to remove as much extraneous material as possible. (2.20 - 3.91) (7.7- 12.7) (0.1 4 - 0.36) Since certain elements accumulate in foliose lichens in zones Soil 23.28 2 17.40 39.5 2 14.7 1.92 2 0.79 according to age, i.e. exposure time (Bargagli et al., 1987b), only the outermost 3 rnm of the thallus were detached and ana- (12.1 - 541 (17.5 -57.1) (1.01 - 2.89) lyzed. This part is physiologically the most active and has an age of about one year (Fisher abd Proctor, 1978). Similarly, to properly compare element concentrations in soils, it is neces- Worldwide, the average soil concentration of As is 6 pdg, sary to analyze the same grain-size fraction in all samples (So- with a typical range of 0.1-55 pg/g (Kabata-Pendias and Pen- cied Italiana della Scienza del Suolo, 1985),and thus, soil sam- dias, 1979). The values measured in the present survey, al- ples were sieved at 250 pm. though within this range, were slightly higher on an average ba- The samples were powdered and homogenized and about sis at all three locations. 150 mg were mineralized in a pressurized digestion system However, As concentrations in soils from Piancastagnaio (Teflon bomb) with concentrated “03 for 10 h at 130°C. were the lowest measured, suggesting that there is no contribu- Trace element concentrations, expressed on a dry weight basis, tion from geothermal activity. This is further confirmed by were determined by: 1) atomic absorption spectrophotometry some unpublished analyses of polluted soils from the geother- using a hydride generator for As and the cold vapor technique mal area of Travale-Radicondoli (central 1taly), which showed for Hg; 2) inductively coupled plasma emission spectrometry concentrations in the range 52.8-63.5 pglg. €or B. Analytical quality was checked by analyzing the Stan- Also in Lichens, As concentrations were included in the dard Reference Materials N. 1572 “citrus leaves” and N. 27 1 1 range reported by Sloof and Wolterbeek ( 199 1) for remote ar- “Montana soil” (NIST,Gaithersburg, USA). eas of the Netherlands (0.5-17 pglg), but on an average basis Prior to statistical procedures, trace element concentrations were higher than the 1.7 pg/g reported by these authors. How- were transformed to logarithms to correct for skewed distribu- ever, the fact that the lowest values were measured at Pian- tions (Bailey, 198 1). Significance of differences between castagnaio and the range of concentrations in the geothennal

138 Loppi area (2.02-3.28 pg/g) matched those reported by G6mez Per- ,., , ...... alta and Chavez Carmona (1995) and Loppi and Bargagli (1996) for the geothermal areas of Los Azufres (Mexico) and 0.9lt n “f Travale-Radicondoli (0.66- 14.32 and 0.19-3.55 pg/g respec- 0 tively), suggests that there is no contribution fkom geothe~al activity. . According to Baker and Chesnin (1 973, normal B levels in soil are in the range of 2-100 pg/g, with an average concentra- 0 tion of about 25 pg/g. Simiiarly for As, values measured in the 0 Abbadla S. Salvatore present survey were in this range but on an average basis were 0 Plancartrgnaio slightly higher at all three locations. Al~oughnot statistically A RemoteSlto I I different, Piancastagnaio had the highest mean value (50.5 0.1 pg/g), which was, however, far below the 132-207 pg/g meas- 0 5 10 15 20 25 30 35 40 45 50 55 60 65 ured in polluted soils fiom the geothermal area of Travale- Hg Soil (pg1g dw) Radicondoli (unpublished data).The same was true for lichens, Figure 1. Mercury content in soil vs. lichens. in. which normal B values are generally in the range of 5-25 pg/g but with an average concentration of 6-10 pgfg (Gouch et al., 1980). The mean B concentratiqn at Piancastagnaio (1 3.1 As far as mercury is concerned, at the Hg mining area of Ab- pg/g) was below the 17.8 and 42 pg/g reported for lichens @om badia S. Salvatore concentrations were extremely high both in the geothermal areas of Travale-Radicondoii (Loppi & Barga- soil and epiphytic lichens, and the anomalous content in these gli, 1996) and Puhimau (Hawaii) (Connor, 1979) respectively. organisms was due to the uptake of elemental mercury originat- According to Adriano (1986), the normal concentration of ing from soil degassing. At the geothermal area of Piancastag- Hg in soil ranges from 0.06-0.20 pg/g, but according to Baroni naio, soil mercury was not different from that in the control et al. (1994), background Hg levels in rocks from southern area, but Hg in lichens was almost twice the control levels, sug- Tuscany are higher, on the order of 0.25 pg/g, with peaks of 1 gesting that the gaseous emissions from the geothennal power pg/g. Mercury levels found in soils in the present survey are de- plants are an important source of air contamination. cidedly high, with the highest value (59.74 pg/g) measured in soil collected at the minespoil. Despite the high values, no sta- References tistical difference was found between soils from the geothermal Adriano, D.C., 1986. Trace elemenfsin the ferreslrialenvironment. Springer, area and the remote area. Berlin. Also in lichens, Hg concent~tionswere affected by the past Armannsson H., Kris~annsd&~ir,H., 1992. Geo~e~alenvi~nmen~ im- mining activity, but in this case, in the geothermal area Hg lev- pact. Geofhermics,2 1: 869-880. els were also higher than in the remote area. Nonnal Hg values Bailey, N.T.J., 198 1. Stafisticalmethodsin biology. Hodder & Stoughton, Lon- in lichens from unpolluted areas not affected by geochemical don. anomaly are generally less than 0.2 pg/g (Gouch et al., 1980). Baker, D.G.,Chesnin L., 1975. Chemical monitoringofsoils.A&. Agron., 27. The very high mean Hg value found at Abbadia S. Salvatore Bargagli, R., losco F.P., Barghigiani C., 1987a Assessment of mercury disper- (1.27 pglg) can only be explained taking into account the de- sal in an abandoned mining area by soil and lichen analysis. ~aferAir Soil PoIIuI., 36: 219-225. gassing of elemental mercury from the soil (Figure l), a fact which has been already reported (Bargagli et al., 1987a). Con- Bargagli, R., losco F.P., D’Amato M.L., 1987b. Zonation oftrace metal accu- mulation in three species ~iongingto the genus Parmelia. C~foga~je centrations of Hg at Piancastagnaio (0.43 pglg) were almost Bryol. Lichhol., 8: 331-337. twice those found in the remote area (0.23 pg/g). According to Barghigiani, C., Ristori T., 1994. Mercury levels in agricultural products of Mt. Bargagli and B~~igiani(1991) and Loppi and Bargagli Amiata (Tuscany, I tafy). Arch. iron. Confam.Tmicol., 26: 329-334. (1 9961, Hg concentrations in lichens from the geothermal areas Baroni F., Protano G.,Riccobono F., 1994. Mercury content of the rocks of of Larderello and Travale-Radicondoli (central Italy) are in the Tuscany. A geochemical contribution to geology of Hg-ores. Afti Accad ranges 0.16-0.82 and 0.05-0.56 pg/g respectively. The range of FisiocrificiSiena, 13: 59-67. concentrations found at Piancastagnaio (0.27-0.69 pg/g) is per- Bombace, M.A.,Cigna Rossi L., Clemente G.F.,Zuccaro-Labellarte G., Alle- fectly in line with these values. In this latter case, the most grini M., Lanzola L., Gatti L., 1973. Ricerca ecologica sulle zone mercurif- ere del Monte Amiata. Igiene SanifhPubblica, 29: 19 1-237. likely source of Hg for epiphytic lichens are the gaseous emis- sions from the geothermal power plants. Bowen, R., 1989. Geothermal resources. Elsevier Applied Science, London. Connor J.J., 1979. Geochemistry of ohiaand soil lichen, Puhimauthermal area, Hawaii. Sci. Total Environ., 12: 241-250. Conclusions Deu M., Kreeb K.H., 1993. Seasonal variations of foliar metal content in three From the results of the present survey it can be concluded fruit species. In: Markert. B. (ed.), Plants as biomonitors. Indicators for heavy metals in the terrestrial environmenf,VCH, Weinheim, 577-591. that the geothe~alpower plants do not represent a rnacro- ENEL, 1996. Team Emissioni e Bilanci di Massa - Relazione di Settore. In: In- scopic source of arsenic and boron contamination in the Mt. dagrne per la valutazione degli efletti sull ‘ambiente delle emissioni aero- Amiata area. disperse degli impianri geofermoele f fricidell ‘area amiafina.

139 Loppi

Fisher, P.J., Proctor M.C.F., 1978. Observations on a season’s growth in Par- Loppi, S., 1996. Lichens as bioindicators of geothermal air pollution in central melia caperafa and P. sulcata in South Devon. Lichenologrst, IO: 8 1-89. Italy. Bryologist, 99: 41-48. Gornez Peralta M., Chbvez Carmona A., 1995. Liquenes como indicadores Loppi, S., Bargagli R., 1996. Lichen biomonitoringof trace elements in ageo- biologicos en el campo Geottrmico Los Azufres, Michoacacan, Mexico. thermal area (central Italy). WaferAir Soil Pollut., 88: 177-187. Geofermiu,11: 137-143. Siegel, M.S.,Siegel B.Z., 1975. Geothermal hazard. Mercury emission. Envi- Gough, L.P., Severson R.C., Jackson L.L., 1988. Determining baseline element ron. Sci Technol. Left., 9: 413. composition of lichens. Water Air Soil Polllut., 38: 157-167. Sloof, J.E., Wolterbeek H.T.,1991. National trace-element air pollution rnoni- Hale, M.H.,1983. The biology of lichens. Edward Arnold, London. toring survey using epiphytic lichens. Lichenologisf,23: 139-165. Kabata-Pendias, A., Pendias H., 1984. Trace elements in soils and plants. Societa ltaliana della Scienza del Suolo, 1985. Metodi normalizzati di analisi CRC, Boca Raton, Florida. del molo. Edagricoie, Bologna.

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