Volcanic and anthropogenic contribution to heavy metal content in lichens from Mt. Etna and Vulcano island (Sicily)

Environmental Pollution 108 (2000) 153±162

www.elsevier.com/locate/envpol

Volcanic and anthropogenic contribution to heavy metal content in lichens from Mt. Etna and Vulcano island (Sicily) D. Varrica a, A. Aiuppa a, G. DongarraÁ a,b,* a

Dipartimento C.F.T.A., UniversitaÁ di Palermo, via Archira® 36, 90123 Palermo, Italy Istituto di Geochimica dei Fluidi del CNR, Via U. La Malfa 153, 90135 Palermo, Italy

b

Received 24 November 1998; accepted 24 August 1999

``Capsule'': Lichens were used to determine element concentrations in relation to natural or anthropogenic sources.

Abstract Major and trace element concentrations were determined in two lichen species (Parmelia conspersa and Xanthoria calcicola) from the island of Vulcano and all around Mt. Etna. In both areas, the average concentrations of Al, Ca, Mg, Fe, Na, K, P and Ti are substantially greater than those of other elements. Several elements (Br, Pb, Sb, Au, Zn, Cu) resulted enriched with respect to the local substrates. The Br and Pb enrichment factors turned out to be the highest among those calculated in both areas. Data indicate that mixing between volcanic and automotive-produced particles clearly explains the range of Pb/Br shown by lichen samples. Sb is also enriched, revealing a geogenic origin at Vulcano and a prevailing anthropic origin at Mt. Etna. Distribution maps of the enrichment factors show a generalized enrichment of Au and Zn near Mt. Etna, whereas Cu appears to be enriched prevalently in the NE±SE area. The highest levels of Au and Cu at Vulcano occur E±SE from the craters, following the prevailing wind direction. # 2000 Elsevier Science Ltd. All rights reserved. Keywords: Lichens; Trace metals; Biomonitoring; Volcanic emissions; Airborne particles

1. Introduction Since the studies of Zoeller et al. (1974) and Duce et al. (1975), it has become clear that continental dust and sea-water spray cannot account for the global dispersion of volatile elements (Hg, Se, Sb, As, Cu, Zn, Pb) in the atmosphere. Airborne particulate sampling in urban areas has revealed that human activities (automotive gasoline, oil and coal combustion, smelter activity) produce and release to the atmosphere large amounts of trace elements (Cawse and Peirson, 1974; Paciga et al., 1975; Harrison and Williams, 1982; Harrison and Sturges, 1983). Volcanoes are also trace element emitters. Studies both on volcanic gases (Stoiber and Rose, 1970; Menyailov and Nikitina, 1980; Gemmel 1987), and particulate matter collected directly

* Corresponding author. Present address: Dipartimento C.F.T.A., UniversitaÁ di Palermo, via Archira® 36, 90123 Palermo, Italy. Tel.: +39-91-6161516; fax: +39-91-6168376. E-mail address: [email protected] (G. DongarraÁ).

from volcanic plumes (Cadle et al., 1973; Mroz and Zoeller, 1975; Lepel et al., 1978; Buat-MeÂnard and Arnold, 1978) have shown that metal elements are separated from magma during degassing and transported by rising gases as halides, native elements or sulfur compounds. Approaching the surface, they condense forming small particles which are then dispersed throughout the atmosphere. Even though volcanic contribution seems to be of little importance for most trace elements on a global scale (Lantzy and Mackenzie, 1979), volcanic-derived particles may become important in areas characterized by active volcanism. For instance, Buat-MeÂnard and Arnold (1978) showed that particulate Cd, Hg, Se, Cu and Zn emitted by the Mt. Etna plume are comparable to the amount of these elements released in the Mediterranean area by anthropogenic sources. Bergametti et al. (1984) carried out an aircraft survey to study the chemical composition of particulate matter in the Mt. Etna plume and its transport in the atmosphere, and were able to identify particulate sulfur at a great distance (260 km) from the emission point. However, Bargagli et al. (1991),

0269-7491/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0269-7491(99)00246-8

154

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

studying the metal content of vegetation on Vulcano island, recognized as negligible the environmental impact of the volcanic emission. In the present paper an attempt is made to estimate the contribution of natural, volcanic and anthropogenic sources to metal contents in lichens from two of the most active volcanic areas in Sicily: the island of Vulcano and Mt. Etna (Fig. 1). The spread of metals in these two sites has also been investigated. A further aim of this paper was to evaluate whether the sole fumarole activity, as occurring at Vulcano island, is a signi®cant source of metals in the surrounding environment. The choice to investigate the areas of Mt. Etna and Vulcano island arose from the consideration that they belong to di€erent geodynamic environments and exhibit signi®cant di€erences in volcanic activity (permanent degassing from open central craters and frequent high volume lava ¯ow eruptions at Mt. Etna versus hydrothermal±volcanic activity at Vulcano). Furthermore, the Mt. Etna area is densely populated with many villages surrounding the lower ¯anks of the volcano and a large town (Catania) at its southeastern corner. The island of Vulcano is, on the other hand, scarcely in¯uenced by

anthropogenic activities, being devoid of industrial activities and with a rather limited automotive trac. Lichen samples were collected over a large area around both volcanic edi®ces and then analysed for major and trace element contents. Lichens have been successfully used in environmental studies concerning air quality and the atmospheric dispersion of volatile compounds (Nieboer et al., 1972; Tuominen and Jaakkola, 1973; Czehura, 1977; Puckett and Finegan, 1980; Garty 1985; Notcutt and Davies, 1989; Bargagli et al., 1991; Nimis et al., 1993). They are characterized by a thallous structure and di€er from higher plants by having neither cuticle nor stomata and by depending on the atmosphere for their nutrition. Their peculiar physiology and morphology force them to absorb and accumulate from the atmosphere chemical elements in gaseous, liquid or particulate form and, owing to the absence of excretion mechanisms, lichens cannot expel them. The whole surface of the thallus is involved in the accumulation process and, since it is exposed to air for long periods of time, metal contents in lichens allow an assessment of the environmental conditions of a certain area over prolonged periods of observation.

Fig. 1. Location of the study areas.

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

2. Study sites, materials and methods 2.1. Geological settings Mt. Etna (3300 m above sea level) is the largest active volcano in Europe. The last considerable eruption occurred in 1991±93. It has grown during the last 500,000 years along tensional faults cutting a thick continental crust. The volcanic pile is mainly composed of alkali basalt±hawaiite lava ¯ows, with more evolved volcanites (trachyte) and pyroclastics locally interposed (Chester et al., 1985). Etna's activity is mostly e€usive and degassing from summit craters continuously releases volatiles into the atmosphere (Allard et al., 1991). The huge amount of volatiles emitted by Mt. Etna was explained by Lambert et al. (1986) and Pennisi and Le Cloarec (1998) by the continuous replenishing of a shallow magmatic chamber by non-degassed magma from depth. Up to now the most complete report on particulate trace elements collected by air ®ltration in the plume of Mt. Etna is that by Buat-MeÂnard and Arnold (1978), who measured concentrations of a large suite of elements revealing high enrichment factors for S, Cl, Br, Se, Hg, Cd, Ag, Au, Zn Cu, Pb, As and Sb. Varekamp et al. (1986) found abundant Al, Fe, Casulfate and sulfuric acid droplets in the volcanic plume. Cu and Zn were also found in most sulfates. Mt. Etna accounts for 1±10% of trace metals emitted by volcanoes on a global scale (Gauthier and Le Cloarec, 1998; Allard et al., in preparation). The island of Vulcano (Northeastern Sicily) belongs to the volcanic arc of the Aeolian Islands. Volcanic activity in the area started around 120,000 years ago (Keller, 1980). Recent activity (younger than 15,000 years) has built up the pyroclastic and lava cone of La Fossa (Frazzetta and La Volpe, 1991). The island is made up of rocks belonging to a shoshonitic series, from basalt to rhyolite. More potassic undersaturated lavas are also present. The last eruption occurred in 1888±90. The present-day volcanic activity consists only of intense hydrothermal activity concentrated round the crater and in the area surrounding the cone. Literature regarding trace elements emitted by the fumarole ®eld on Vulcano island is quite scanty. The sole exceptions are data from analyses of sublimates (Garavelli et al., 1993; Garavelli, 1994) and condensates (Piccardi et al., 1979; Brondi and Dall'Aglio, 1991; Pennisi et al., 1997), which usually refer to only a few elements. The identi®ed minerals in sublimates include cannizzarite (Pb46Bi54S217), galenobismuthite (PbBi2S4), cotunite (PbCl2), sphalerite (ZnS), pyrite (FeS2), lillianite (Pb3Bi2S6) and greenockite (CdS) (Martini et al., 1988; Garavelli et al., 1993; Ferrara et al., 1995). High contents of bromine have been observed in collected salammoniac sublimates (Coradossi et al., 1996), where bromine substitutes for chlorine. The occurrence of Cu, Zn, Cd, Sb, Bi and Pb in condensates

155

has been documented by Piccardi et al. (1979), who attributed the presence of these trace elements to the reaction of acidic solutions with the wallrock. The presence of mercury and other trace elements in vegetation from Vulcano island and Mt. Etna was investigated by Bargagli et al. (1991) and Barghigiani et al. (1988). Notcutt and Davies (1989) related the presence of Cu, Fe, Mg, Mn, Zn and F in lichen samples collected on the upper ¯anks of the volcano to the spread of the Mt. Etna plume. 2.2. Material and analytical techniques A total of 147 lichen samples, 50 from Vulcano and 97 from Mt. Etna, were collected during a 1-year survey (1997±98). The sampling sites are indicated in Figs. 4 and 5. Two lichen species (Parmelia conspersa (Ehrh) Ach. and Xanthoria calcicola Ochsner), collected on rocky substrate, were used in this study. At Vulcano island only samples of P. conspersa were collected. At Mt. Etna 37 samples of P. conspersa were collected and 60 samples of X. calcicola. Several di€erently orientated thalli were collected from each of the 147 sampling sites. These two lichen species were chosen for sampling since they are widespread throughout the survey area and because it has been demonstrated to be in general agreement with the chemical data from these two species (DongarraÁ et al., 1995; Carrot et al., 1996). Both species belong to the `foliose' growth-form categories for lichens. These lichen species can be lifted easily and almost free from the rocky surface. Samples were always removed from the substrate using wooden knives. They were ®rst air-dried at room temperature and then oven-dried at 40 C for 24 h. Lichens were sorted and cleaned of debris and soil with a toothbrush and small wooden sticks under a low magni®cation stereomicroscope. No lichen samples were found on Mt. Etna at an altitude higher than 1800 m above sea level, and on the Vulcano crater. All the elements were analyzed at Activation Lab. Ltd (Canada), by instrumental neutron activation analysis (INAA), except Ca, Zn, Cu, Pb, Ni, Mn, Sr, V, P, Mg, Ti and Al which were analyzed by ICP±MS. NBS 1572 `citrus leaves' and 1632 B were used as standard reference materials. Several replicates yielded a precision of 20% for trace elements and in the range 5±10% for the main components. Some descriptive statistical parameters of major and trace elements in lichens are listed in Table 1. 2.3. Factoring method A subset of 17 element concentrations from each studied area was subjected to factor analysis (principal component method of factoring) examining the relationship between variables (R-mode of analysis). Only a few main lithogenic constituents were introduced in the

156

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

Table 1 Average and variation coecient (CV%) of the analysed elementsa Etna

Au As Br Ca Co Cr Cs Fe K Mo Na Ni Rb Sb Sc Se Sr Th U Zn Cu Pb Mn V P Mg Ti Al Y

Table 2 Varimax rotated factor matrix for the lichen samples from Mt. Etnaa

Vulcano

Average

CV%

Average

CV%

0.018 2 31 20,668 5 14 0.8 9755 6485 0.90 2600 8 20 1.3 3 1.4 120 2.2 0.6 146 43 57 169 29 762 3423 1162 14,619 7

148 62 58 80 60 77 87 74 48 88 61 72 60 130 61 53 46 64 62 107 100 95 67 51 55 55 48 64 43

0.044 5 37 17,968 6 17 1.8 9858 9377 2.0 3525 7 36 0.6 4 1.5 171 5 1.9 128 117 37 247 36 1312 3932 846 17,964 14

142 53 46 63 54 50 66 110 44 61 72 82 58 66 70 85 86 72 60 34 109 87 76 66 25 73 61 64 74

a Concentrations are expressed in mg/kg (dry wt). The variation coecient is the ratio: SD/mean.

analysis, in order to reduce its complexity and to facilitate interpretation of extracted factors. The number of factors to be extracted was determined by the Kaiser criterion which deletes all factors with an associated eigenvalue of less than 1. This means to retain all factors which contain greater variance than the original standardized variables. To bring the complexity of a variable to a minimum, the extracted factors were rotated according to the Varimax procedure, which maximizes the variance of the squared loadings in each column. Tables 2 and 3 present the terminal solutions of orthogonally rotated factors, along with the associated eigenvalues and communalities. These latter indicate to what extent the factors account for the variance of each variable. 2.4. Enrichment factors To better understand the complex data sets, enrichment factors (EFs) were calculated for all the elements according to the following equation (Puckett and Finegan, 1980): EF ˆ …X=Al†lich: =…X=Al†subst: ;

…1†

Factor Factor Factor Factor Communalities 1 2 3 4 Al As Au Br Ca Cr Cs Cu K Na Mg Pb Rb Sb Sc Ti Zn Eigenvalues % expl. variance Cumulative expl. variance (%)

0.95 0.70 ÿ0.19 0.27 ÿ0.23 0.87 0.88 0.08 0.92 0.74 0.91 ÿ0.06 0.91 0.19 0.91 0.78 0.17

0.05 0.35 0.27 0.75 ÿ0.01 0.30 0.07 0.10 0.01 0.29 0.20 0.68 0.02 0.87 0.17 0.25 0.74

ÿ0.04 0.20 0.52 0.14 ÿ0.82 0.07 0.19 ÿ0.08 0.04 0.02 ÿ0.01 ÿ0.58 0.08 0.05 0.03 ÿ0.12 0.01

0.03 0.02 0.37 0.04 0.19 ÿ0.10 ÿ0.14 0.87 ÿ0.06 0.31 0.08 0.06 ÿ0.14 0.06 0.14 0.29 0.11

7.68 0.45 0.45

2.85 0.17 0.62

1.41 0.08 0.70

1.22 0.07 0.77

0.91 0.66 0.51 0.66 0.76 0.86 0.84 0.78 0.85 0.74 0.88 0.79 0.84 0.80 0.88 0.77 0.59

a For each column are also reported the associated eigenvalue, the percentage of total variance accounted for by the factor and the cumulative percentage.

where X and Al refer, respectively, to the concentrations of the element of interest and of the reference element in the lichen sample (lich.) and in the local substrate (subst.). Al was used as reference element as it is a wellde®ned crustal element and shows very low chemical reactivity. An element is considered enriched when its EF exceeds 1. Nevertheless, caution must be exercised in the choice of the threshold value as, besides various contributions to metal contents in lichens, two other factors may increase the variance of the enrichment factors: experimental error in analytical determinations, and the intrinsic variance of the element/Al ratio in the substrate taken as reference material. The level of possible analytical error was estimated at approx. 20% for trace elements and in the range of 5±10% for the main components. Considering that the relative error of a generic quotient L=X/Y is less than or equal to the sum of relative error which a€ects each determination of X and Y, we may assume that a reasonable estimate of the error level in the numerator of Eq. (1) is in the 30±40% range. Uncertainty in the denominator may be more serious, due to the large variability in trace element contents of rocks even of similar bulk composition. To minimize this last type of error, average compositions of volcanites from Mt. Etna and Vulcano island were, respectively, computed from large sets of analyses reported in the literature (Cristofolini et al., 1991; Barbieri et al., 1993; Treuil et Joron, 1994; Tonarini et al., 1995, for Mt. Etna; Keller, 1980, for Vulcano island). In

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162 Table 3 Varimax rotated factor matrix for the lichen samples from Vulcano islanda

Al As Au Br Ca Cr Cs Cu K Na Mg Pb Rb Sb Sc Ti Zn Eingevalues % expl. variance Cumulative expl. variance (%)

Factor 1

Factor 2

Factor 3

Communalities

0.90 0.08 0.66 0.10 0.17 0.58 0.91 ÿ0.03 0.94 0.91 0.78 0.01 0.86 ÿ0.23 0.54 0.83 ÿ0.14

0.37 0.57 ÿ0.05 0.04 0.72 0.64 ÿ0.12 0.72 ÿ0.02 0.24 0.51 0.13 ÿ0.06 0.01 0.74 0.36 0.50

ÿ0.13 0.23 0.55 0.64 0.03 0.17 ÿ0.04 ÿ0.39 ÿ0.04 0.02 ÿ0.16 0.70 0.19 0.37 ÿ0.10 ÿ0.10 0.19

0.97 0.38 0.73 0.42 0.55 0.78 0.84 0.68 0.89 0.88 0.89 0.51 0.78 0.19 0.86 0.83 0.31

6.55 0.39 0.39

3.20 0.19 0.58

1.71 0.10 0.68

a For each column are also reported the associated eigenvalue, the percentage of total variance accounted for by the factor and the cumulative percentage.

addition, Fig. 2, showing the average EF for each element in lichens from Mt. Etna and Vulcano island, highlights two groups of elements. The ®rst, including the non-volatile elements (often termed lithophiles), is characterized by an average EF of 1.5 and a standard deviation (s) of 0.7; the second group contains the elements Br, Pb, Sb, Au, Zn and Cu, with an average EF greater than 3, which represents the aforementioned mean value (1.5) plus 2s. Therefore, at a signi®cance level of 5% (a=0.05), the origin of these last elements appears to be di€erent from the lithophile elements and they may be considered enriched with respect to the local crustal source. These ®ndings are consistent with the results of the previous multivariate analysis. An attempt is made in the following section to identify the sources of these elements and their spread in the surrounding environment. Our approach is mainly based on the results of factor analysis, the computed EFs and some typical element ratios. 3. Discussion In both areas, the average concentrations of Al, Ca, Mg, Fe, Na, K, P and Ti are substantially greater than those of other elements. These typical crustal elements account for more than 95% in weight of all the elements analysed. A signi®cant in¯uence of Na and Mg from the

157

marine environment can be ruled out on the basis of the computed EFs (see below). Factor analysis of the Etna data attributed 76% of the total variance in the chemistry of the lichens to four factors (Table 2). The signi®cant high positive loadings of the crustal elements Al, As, Cr, Cs, K, Na, Mg, Rb, Sc, and Ti on factor 1, which explain 44% of the total variance, point to the dominant contribution of soilderived aerosols. The association of Pb, Br, Sb and Zn is re¯ected on factor 2, explaining 15% of the total variance. These elements may be volcanic or anthropic in origin. Eight per cent of the total variance is accounted for by factor 3, where Ca and Pb are present with high negative loadings. This factor reveals no much additional details other than an indication that Ca, in spite of being one of the most abundant crustal elements, shows low correlations with the other lithophile elements of factor 1. The signi®cant loadings of Pb on factors 2 and 3 also indicate two independent sources for this element. The last factor is entirely dominated by Cu and, subordinately, by Au. Although Na shows a factor loading on this factor as high as Au, most of its variance is explained by factor 1. Three factors, explaining approximately 68% of the total variance, were extracted from Vulcano island data (Table 3). Most of the elements exhibit high factor loadings on both factors 1 and 2, making it dicult to attribute a geochemical meaning to these factors. On the other hand, factor 3 shows the Pb±Br association already observed in the Etna samples, and it probably represents volcanic emissions, since pollution sources can be ruled out to a large extent. Fig. 2 shows that the same elements are enriched at Vulcano (Br>Pb>Sb>Zn>Au>Cu) and at Mt. Etna (Br>Pb>Sb>Zn>Au>Cs>As, Ni, Cu). The Br and Pb EFs computed in this study for the lichens of Vulcano and Etna are by far the highest among those calculated in both areas. They average, respectively, 72 and 13 at Vulcano and 76 and 49 at Mt. Etna. One of the most important emission sources of Pb into the earth's atmosphere is the combustion of gasoline, to which Pb is added in tetra-alkyl form due to its anti-knock properties. Automotive particulate also represents a signi®cant source of bromine in the atmosphere as it is added to gasoline to reduce the formation of Pb oxides inside automotive engines. According to gasoline composition, the Br/Pb mass ratio in fresh automotive-produced leaded particles should be around 0.39 (Harrison and Sturges, 1983; Sturges and Harrison, 1986). This ratio, termed `ethyl ratio', is generally assumed as a `marker' of aerosols produced by gasoline combustion. In the study areas, sea spray and volcanic emissions are also potential sources of Br. Br is commonly associated with other halogens (Cl, F) in volcanic gases. Cawse (1975) explained the high Br content in air particulates collected in the UK during January±March

158

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

Fig. 2. Average enrichment factors (EFs) for the analysed elements in lichen samples from Mt. Etna and Vulcano island. EFs have been calculated using Al as the reference element and average concentrations in local rocks taken from the literature. The dashed line indicates the boundary, at a signi®cance level of 5% (a=0.05), between enriched and non-enriched elements.

1973 as partly due to particles emitted during the eruption of Heimaey volcano in Iceland. Buat-MeÂnard and Arnold (1978) estimate a Br ¯ux of 3200 t/year and a Pb ¯ux of 130 t/year from Mt. Etna. Estimated ¯uxes for Vulcano (0.078 t/year for Br and 0.01 t/year for Pb, respectively) are considerably lower (Martini et al., 1988). A correction for sea spray contribution has been applied to our data by the following equation: Br ˆ Brtot ÿ …Br=Na†sea  Nalich

…2†

However, the calculated Br non-marine concentration (Br*) is underestimated because the previous equation assumes that all the sodium in lichen samples comes from sea water. Fig. 3 is a plot of Pb/Br* ratios versus Pb absolute concentrations in the analysed lichens. Many sample points cluster close to the ethyl ratio (here as Pb/Br =2.7) suggesting that deposition of automotive particles is a process occurring in both areas. However, very low ratios are also observed. The range of variability for the Pb/Br ratio in some volcanic ¯uids is also plotted in Fig. 3, for comparative purposes. Buat-Menard and Arnold (1978) give a Pb/Br ratio of 0.057 for the particles collected from the Etna plume. The values (from 0.3 to 0.57) measured by the same authors in particulate matter collected near high-temperature manifestations (hornitos and hot vents) are similar to those shown by gases released by other volcanoes (Stoiber and Rose, 1970; Gemmel, 1987). Fig. 3 clearly indicates that mixing between volcanic particles and automotive-produced

Fig. 3. Pb/Br* ratio versus total Pb (ppm) in lichen samples from Mt. Etna and Vulcano island. Br* is the Br concentration after correction for sea water contribution. The ethyl ratio (Pb/Br=2.7) and the observed range in earth's volcanic ¯uids are also shown.

particles explains the range of Pb/Br shown by lichen samples. Distribution maps of the Pb/Br* ratio are shown in Fig. 4. At Mt. Etna, the anthropogenic

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

159

Fig. 4. Distribution maps of Pb/Br* at Mt. Etna and Vulcano island. Br* is the Br concentration after correction for sea water contribution.

contribution is more signi®cant near the town of Catania and along the main roads. Lowest Pb/Br* ratios are observed on the highest slopes of the volcano. At Vulcano, the highest Pb/Br* ratios are observed in the lichen samples collected along a road connecting the village with the inner part of the island. After Br and Pb, Sb is by far the most enriched element found at Vulcano and Mt. Etna. Average EFs for Sb are considerably higher at Mt. Etna (EF=37) than at Vulcano (EF=9). As indicated by factor analysis, Sb is mainly correlated with Pb and Br in both areas. While at Vulcano island Sb seems to have mainly a geogenic origin, the high EFs of Sb at Mt. Etna are mainly due to anthropogenic sources as the observed Pb/Sb ratio in lichens is in the same range (20±40) found in aerosol samples collected in urban areas of Sicily (Aiuppa et al., in preparation) and in other towns (Bonanni et al., 1992). Among the most common elements present in volcanic plumes and high-temperature fumaroles are Au, Cu and Zn (Lepel et al., 1978; Symonds et al., 1987; Gemmel, 1987; Zreda-Gostynska et al., 1997). Table 1 indicates the general higher contents of Au and Cu in lichens from Vulcano island than from Mt. Etna. Distribution maps of the EFs of Au, Cu and Zn are shown in Fig. 5. Generalized enrichment of Au and Zn may be recognized in the Etnean area, probably because they are in¯uenced both by natural and anthropogenic sources, while Cu is mainly enriched in the NE±SE area. With regard to the latter element, a very high EF (356) was obtained by Vie le Sage (1983) from a hornito at 400 C, situated along the southeast crater of Mt. Etna.

Notcutt and Davies (1989) showed that high concentrations of copper in lichens may be recognized east and northeast of the main craters and related such an anomaly, as well as the presence of ¯uorine, to the spread of plume in the wake of prevailing winds. With respect to the island of Vulcano, it may be observed that Zn is enriched over the whole survey area and, particularly, in the eastern part. Similarly, the highest levels of Au and Cu occur E±SE of the crater, following the prevailing wind direction on the island. Signi®cant anomalies of Cu and Zn were also observed by Bargagli et al. (1991) in surface soils and pine needles from Vulcano. Resuspension of dust from outcropping hydrothermal deposits, enriched in Cu, Zn and Au (Fulignati and Sbrana, 1998), cannot be ruled out. Finally, the Ca±Pb association, as indicated by factor analysis of Mt. Etna data, suggests that automobile fuel combustion may produce the slight EF of Ca (EF=3). Silva and Prather (1997) have shown that 60% of the inorganic particles produced by old vehicles are characterized by the chemical association Pb±Ca. Ca is believed to be a remnant of the re®ning process, as it is contained to a large extent in crude oil. Industrial activities near Mt. Etna may also explain the slight enrichment observed for Ni (average EF=3). 4. Conclusions Two di€erent groups of elements have been recognized in the analyzed lichens: the lithophile elements,

160

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

Fig. 5. Distribution maps of Au, Cu and Zn enrichment factors (EFs) for (a) Vulcano island and (b) Mt. Etna.

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

derived from the local crustal material, and the enriched elements (Sb, Br, Pb, Zn, Au, Cu), forming volatile compounds and mainly originating from anthropogenic sources and/or volcanic gases. Among the latter, Pb, Br and Sb concentrations in lichens seem to be considerably a€ected by human activities. However, the EFs observed for Pb and Br in lichens cannot be attributed exclusively to automotive fuel combustion, but are partly the result of volcanic exhalations. This is more evident on the island of Vulcano, where the anthropogenic in¯uence is very limited. The di€usion of Br is surprising since, apart from any marine contribution, it occurs in the air at very great distances from possible sources of emission. From an environmental viewpoint this presents a particularly important problem concerning the background levels in air currently reached by Br. Cu, Au and Zn contents are mainly derived from volcanic degassing. It appears from this study that their dispersion is related to distance from craters as well as the prevailing wind direction. Comparison between the chemical data reported in the literature and those obtained during the present research, provided in a manner completely independent of other conventional methods, con®rms that volcanoes are a continuous source of trace elements injected into the atmosphere: erroneously, it is believed that they are only responsible for the emission of metals and other elements during eruptive phases. Fumarole activity, as the data regarding the island of Vulcano suggest, may be a signi®cant source of metals in the surrounding environment. In towns and cities near volcanic areas, natural emissions are added to those due to anthropogenic activity. Therefore, both geogenic and anthropogenic sources must be taken into account when planning environmental controls. The results obtained in this work show that a signi®cant part of the atmospheric aerosol deposited on lichens derives from weathering of rocks and from transport of the ®nest material by winds. Although this circumstance may constitute a disadvantage in using lichens, as soil contribution may obscure the e€ects of di€erent metal sources, they still remain useful, simple and cheap sampling media for mapping the dispersal of some environmental contaminants. Acknowledgements The authors would like to thank two anonymous reviewers who signi®cantly improved the quality of this paper by their insightful comments. This research was supported by the Italian National Council of Research (CNR) - Istituto di Geochimica dei Fluidi, which the authors whish to thank. Financial support was also provided by MURST (funds 60%).

161

References Allard, P., Carbonnelle, J., Dajlevic, D., Le Bronec, J., Morel, P., Robe, M.C., Maurenas, J.M., Faivre-Pierret, R., Martin, D., Sabroux, J.C., Zettwoog, P., 1991. Eruptive and di€use emissions of CO2 from Mount Etna. Nature 351, 387±391. Barbieri, M., Cristofolini, R., Delitala, M.C., Fornaseri, M., Romano, R., Taddeucci, A., Tolomeo, L., 1993. Geochemical and Sr-isotope data on historic lavas of Mount Etna. J. Volc. Geotherm. Res. 56, 57±69. Bargagli, R., Barghigiani, C., Siegel, B.Z., Siegel, S.M., 1991. Trace metal anomalies soils and vegetation on two active island volcanoes: Stromboli and Vulcano (Italy). Sci. Total Environ. 102, 209±222. Barghigiani, C., Bargagli, R., Siegel, B., Siegel, S., 1988. Source and selectivity in the accumulation of mercury and other metals by the plants of Mt. Etna. Water, Air and Soil Pollution 39, 395±408. Bergametti, G., Martin, D., Carbonnelle, J., Faivre-Pierret, R., Vie Le Sage, R., 1984. A mesoscale study of the elemental composition of aerosols emitted from Mt. Etna Volcano. Bull. Volcanol. 47-4 (2), 1107±1114. Bonanni, P., Di Paolo, C., Doytchinov, S., Falchi, G., Galletti, M., Gragnani, R., Michetti, I., Tidei, F., Turi, E., 1992. Attribuzione di elementi maggiori ed in traccia contenuti nel particolato atmosferico alle diverse sorgenti di emissione nell'aria di Civitavecchia. Risultati preliminari. In: ENEA Report RT/AMB/92/24, 60. Brondi, M., Dall Aglio, M., 1991. Evolution of mercury, arsenic, antimony, radon and helium contents in ground waters and fumaroles since 1983 through 1989 at Vulcano Island (Southern Italy). Acta Vulcan. 1, 233±241. Buat-MeÂnard, P., Arnold, M., 1978. The heavy metal chemistry of atmospheric particulate matter emitted by Mount Etna volcano. Geophys. Res. Lett. 5 (4), 245±248. Cadle, R.D., Wartburg, A.F., Pollak, W.H., Gandrup, B.W., Shedlovsilk, J.P., 1973. Trace costituents emitted to atmosphere by Hawaiian volcanoes. Chemosphere 6, 231±234. Carrot, F., Clocchiatti, R., Deschamps, C., Grasso, M.F., 1996. Les lichenes capteurs naturels des particules d'origine volcanique: le cas de volcans actives du sud de l'Italie. In: Proceedings of the Symposium on ``Methodologie en matiere de bioindication lichenique''. Ass. Franc. de Lich. Fontainebleau, March 1996. Cawse, P.A., 1975. Anomalous high concentrations of particulate bromine in the atmosphere of the UK. Chemosphere 2, 107±112. Cawse, P.A., Peirson, D.H., 1974. A survey of atmospheric trace elements in the U.K., 1972±1973. UKAEA Harwell Report R7669, HMSO. Chester, D.K., Duncan, A.M., Guest, J.E., Kilburn, C.R.J., 1985. Mount Etna: the anatomy of a volcano. Chapman and Hall, London. Coradossi, N., Garavelli, A., Salamida, M., Vurro, F., 1996. Evolution of the Br/Cl ratios in fumarolic salammoniac from Vulcano (Aeolian Islands, Italy). Bull. Volcanol. 58, 310±316. Cristofolini, R., Corsaro, R.A., Ferlito, C., 1991. Variazioni petrochimiche nella successione etnea: un riesame in base a nuovi dati da campioni di super®cie e da sondaggi. Acta Vulcanol. 1, 25±37. Czehura, S.J., 1977. A lichen indicator of copper mineralization, Lights Creek District, Plumas County, California. Econ. Geol. 72, 796±803. DongarraÁ, G., Ottonello, D., Sabatino, G., Triscari, M., 1995. Use of lichens in detecting environmental risk and in geochemical prospecting. Environ. Geol. 26, 139±146. Duce, R.A., Ho€man, G.L., Zoeller, W.H., 1975. Atmospheric trace metals at remote northern and southern hemispheric sites: pollution or natural? Science 187, 59±61. Ferrara, G., Garavelli, A., Pinarella, L., Vurro, F., 1995. Lead isotope composition of the sublimates from the fumaroles of Vulcano

162

D. Varrica et al. / Environmental Pollution 108 (2000) 153±162

(Aeolian Island, Italy): inferences on the deep ¯uid circulation. Bull. Volcanol. 56, 621±625. Frazzetta, G., La Volpe, L., 1991. Volcanic history and maximum expected eruption at ``La Fossa di Vulcano'' (Aeolian Island, Italy). Acta Vulcanol. 1, 107±113. Fulignati, P., Sbrana, A., 1998. Presence of native gold and tellurium in the active high-sul®dation hydrothermal system of the La Fossa volcano (Vulcano, Italy). J. Volcanol. Geotherm. Res. 86, 187±198. Garavelli, A., 1994. Mineralogia e geochimica di fasi vulcaniche condensate. I sublimati dell'isola di Vulcano tra il 1990 ed il 1993. PhD thesis, University of Bari, Bari. Garavelli, A., Garbarino, C., Laviano, R., Vurro, F., 1993. Solfuri e solfosali tra i prodotti di deposizione dell'area craterica di Vulcano± Isole Eolie (ME). Plinius 10, 161±162. Garty, J., 1985. The amount of heavy metals in some lichens of the Negev Desert. Environ. Poll. 10B, 287±300. Gauthier, P.J., Le Cloarec, M.F., 1998. Variability of alkali and heavy metal ¯uxes released by Mt. Etna volcano, Sicily, between 1991 and 1995. J. Volcanol. Geotherm. Res. 81, 311±326. Gemmel, J.B., 1987. Geochemistry of metallic trace elements in fumarolic condensates from Nicaraguan and Costa Rica volcanoes. J. Volcanol. Geotherm. Res. 33, 161±181. Harrison, R.M., Sturges, W.T., 1983. The mesurement and interpretation of Br/Pb ratios in airborne particles. Atmos. Environ. 17, 311±328. Harrison, R.M., Williams, C.R., 1982. Airborne cadmium, lead and zinc at rural and urban sites in North-west England. Atmos. Environ. 16, 2669±2681. Keller, J., 1980. The island of Vulcano. Rend. Soc. It. Miner. Petrol. 36 (1), 369±414. Lambert, G., Le Cloarec, M.F., Ardouin, B., Le Roulley, J.C., 1986. Volcanic emissions of radionuclides and magma dynamics. Earth Planet. Sci. Lett. 76, 185±192. Lantzy, J.R., Mackenzie, F.T., 1979. Atmospheric trace metals: global cycles and assessment of man's impact. Geochim. Cosmochim. Acta 43, 511±525. Lepel, E.A., Stefansson, K.M., Zoeller, W.H., 1978. The enrichment of volatile elements in the atmosphere by volcanic activity: Augustine volcano, 1976. J. Geophys. Res. 83, 6213±6220. Martini, M, Capaccioni, B., Giannini, L., 1988. Past and present in¯uence of volcanic systems on the surface environments: Vulcano and Lipari (Eolian islands, Italy). Boll. GNV, 383±391. Menyailov, I.A., Nikitina, L.P., 1980. Chemistry and metal contents of magmatic gases, the Tolbachik volcanoes gas (Kamchatka). Bull. Volcanol. 43, 197±207. Mroz, E.J., Zoeller, W.H., 1975. Composition of atmospheric particulate matter from the eruption of Heimaey, Iceland. Science 180, 461±464. Nieboer, E., Ahmed, H.M., Puckett, K.J., Richardson, D.H.S., 1972. Heavy metal content of lichens in relation to distance from a nickel smelter in Sudbury, Ontario. Lichenologist 5, 292±304. Nimis, P.L., Castello, M., Perotti, M., 1993. Lichens as bioindicators of heavy metal pollution: a case study at La Spezia (North Italy). In: Markert, B. (Ed.), Plants as Biomonitors. Indicators for Heavy Metals in the Terrestrial Environment. VCH, Weinheim, pp. 265±284.

Notcutt, G., Davies, F., 1989. The environmental in¯uence of a volcanic plume, a new technique of study, Mount Etna, Sicily. Environ. Geol. Water Sci. 14 (3), 209±212. Paciga, J.J., Roberts, M., Jervis, R.E., 1975. Particle size distribution of lead, bromine and cloride in urban-industrial aerosols. Envir. Sci. Technol. 9, 1141±1144. Pennisi, M., Le Cloarec, M.F., 1998. Variations of Cl, F and S in Mount Etna's plume, Italy, between 1992 and 1995. J. Geoph. Res. 103, 5061±5066. Pennisi, M., Tonarini, S., Ferrara, G., Leeman, W.P., 1997. Contenuto e composizione isotopica del Boro nei condensati fumarolici della Fossa di Vulcano. Atti del Convegno GNV, Roma 3±5 March 1997. Piccardi, G., Martini, M., Legittimo Cellini, P., 1979. On the presence of Cu, Zn, Cd, Sb, Bi and Pb in the fumarolic gases of Vulcano (Aeolian Island). Soc. Ital. di Min. e Petr. 35, 627±632. Puckett, K.J., Finegan, E.J., 1980. An analysis of the element content of lichens from the Northwest Territories, Canada. Can. J. Bot. 58, 2073±2088 . Silva, P.J., Prather, K.A., 1997. On-line characterization of individual particles from automobile emissions. Environ. Sci. Technol. 31, 3074±3080. Symonds, R.B., Rose, W.I., Reed, M.H., Lichte, F.E., Finnegan, D., 1987. Volatilization, transport and sublimation of metallic and non metallic elements in high temperature gases at Merapi Volcano, Indonesia. Geochim. Cosmochim. Acta 51, 2083±2101. Stoiber, R.E., Rose, W.I., 1970. The geochemistry of Central American volcanic gas condensates. Geol. Soc. Am. Bull. 81, 2891±2912. Sturges, W.T., Harrison, R.M., 1986. Bromine:lead ratios in airborne particles from urban and rural sites. Atmos. Environ. 20, 577±588. Tonarini, S., Armienti, P., D'Orazio, M., Innocenti, F., Pompilio, M., Petrini, R., 1995. Geochemical and isotopic monitoring of Mt. Etna 1989±1993 eruptive activity: bearing on the shallow feeding system. J. Volcanol. Geotherm. Res. 64, 95±115. Tuominen, Y., Jaakkola, 1973. Absorption and accumulation of mineral elements and radioactive nuclides. In: Ahmadjiian, V., Hale, M.E. (Eds.), The Lichens. Academic Press, London, pp. 185± 223. Treuil, M., Joron, J.L., 1994. Etude geÁochimique des eÂleÂments en traces dans les laves eÂmises au cours de l'eÂruption 1991±1993 de l'Etna. Mise en evidence des contributions de la source, de la fusion partielle, de la di€erenciation et des modaliteÂs de transfert des magmas. Acta Vulcanol. 4, 29±45. Varekamp, J.C., Thomas, E., Germani, M., Buseck, P.R., 1986. Particle geochemistry of volcanic plumes of Etna and Mount St. Helens. J. Geophys. Res. 91 (B12), 12,233±12,248. Vie Le Sage, R., 1983. Chemistry of the volcanic aerosols. In: Tazie€, H., Sabroux, J.C. (Eds.), Forecasting volcanic events. Elsevier, pp. 445±474. Zoeller, W.H., Gladney, E.S., Duce, R.A., 1974. Atmospheric concentrations and sources of trace metals at the South Pole. Science 183, 199±201. Zreda-Gostynska, G., Kyle, P.R., Finnegan, D., Prestbo, K.M., 1997. Volcanic gas emissions from Mount Erebus and their impact on the Antarctic environment. J. Geophys. Res. 102 (B7), 15,039±15,055.