doi:10.1016/j.jvolgeores.2007.04.013
Copyright © 2007 Elsevier B.V. All rights reserved.
Environmental impact of magmatic fluorine emission in the Mt. Etna area
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Sergio Bellomoa, b, 
, 
, Alessandro Aiuppaa, b, Walter D’Alessandrob and Francesco Parelloa
aDipartimento CFTA, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy
bIstituto Nazionale di Geofisica e Vulcanologia, Sezione di Palermo, via La Malfa 153, 90146 Palermo, Italy
Received 5 April 2006;
accepted 23 April 2007.
Available online 17 May 2007.
Abstract
The sustained and uninterrupted plume degassing at Mount Etna volcano, Southern Italy, represents the troposphere's most prominent natural source of fluorine. Of the 
200 Mg of fluorine (as HFg) emitted daily by the volcano, 1.6 ± 2.7 Mg are deposited by wet and dry deposition. Fluorine-deposition via volcanic ash, here characterised for the first time, can be quite significant during volcanic eruptions (i.e. 60 Mg of fluorine were deposited during the 2001 eruption through volcanic ash, corresponding to 85% of the total fluorine deposition). Despite the fact that these depositions are huge, the fate of the deposited fluorine and its impact on the environment are poorly understood. We herein present original data on fluorine abundance in vegetation (Castanea Sativa and Pinus Nigra) and andosoils from the volcano's flank, in the attempt to reveal the potential impact of volcanogenic fluorine emissions. Fluorine contents in chestnut leaves and pine needles are in the range 1.8–35 μg/g and 2.1–74 μg/g respectively; they exceed the typical background concentrations in plants growing in rural areas, but fall within the lower range of typical concentrations in plants growing near high fluorine anthropogenic emission sources. The rare plume fumigations on the lower flanks of Mt Etna (distance > 4 km from summit craters) are probably the cause of the “undisturbed” nature of Etnean vegetation: climatic conditions, which limit the growth of vegetation on the upper regione deserta, are a natural limit to the development of more severe impacts. High fluorine contents, associated with visible symptoms, were only measured in pine needles at three sites, located near recently-active (2001 to 2003) lateral eruptive fractures. Total fluorine contents (FTOT) in the Etnean soils have a range of 112–341 μg/g, and fall within the typical range of undisturbed soils; fluorine extracted with distilled water (FH2O) have a range of 5.1 to 61 μg/g and accounts for 2–40% of FTOT. FH2O is higher in topsoils from the eastern flank (downwind), while it decreases with depth in soil profiles and on increasing soil grain size (thereby testifying to its association with clay–mineral-rich, fine soil fractions). The fluorine adsorption capacity of the andosoils acts as a natural barrier that protects the groundwater system.
Keywords: Mt. Etna; fluorine; environmental volcanology; impact of volcanic F; soils; vegetation; volcanic ash
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Fig. 1. Location of the sampling sites. Right: a sketch of Mt Etna's area. The grey bold line represents the limits the Etnean volcanic products; the bold dashed line shows the border of the horseshoe-shaped valley named “Valle del Bove”. Left: zoom of Etna's summit area (covered area, 15 × 15 km). The summit craters are labelled as NE — North-East Crater; SE — South-East Crater; BN — Bocca Nuova; VOR — Voragine. Soil sampling sites discussed with more detail in the text are also indicated with their initials (L — Leccio; R — Roverella; F — Faggio: E3 — Etna3; E5 — Etna5) or with a number (31, 35 and 48). SAS, CIT and PRO are three vegetation sampling sites with peculiar features (see text). On the basis of the wind rose from 700 hPa (bottom right — Birgi station dataset of the period 2001–2003), the sampling sites were subdivided in downwind (diamonds — from 22°50′ to 202°50′ on the eastern flank) and upwind (squares — western flank) with respect to the summit crater's emissions. Some of the sites were sampled for more than one media; in this case the symbols are nested.
Fig. 2. Isolines of fluorine deposition (g/m2) via volcanic ash on the south-eastern flank of Mt. Etna during the 2001 eruption.
Fig. 3. (a) Soluble fluorine on the ashes of the 2001 eruption versus grain-size (Φ = − log2 grain-size in mm); thick marks are median values of the grain-size class. Variation with distance from the eruptive vent of (b) fluorine concentration in ash leachates and (c) total soluble fluorine deposition, are also shown.
Fig. 4. Variation with distance from the summit craters of (a) Hydrogen fluoride in air (data from Aiuppa et al., 2004a); (b) fluoride bulk deposition (data from Aiuppa et al., 2006); (c) fluorine content in chestnut leaves; (d) fluorine content in pine needles; (e) water extractable, (f) oxalate extractable and (g) total fluorine in topsoils. Samples collected downwind with respect to the summit crater are shown as grey diamonds, while those collected upwind as black squares. The line labelled as dl in graph (a) indicates the detection limit of the method. The encircled samples in (d) are discussed further in Fig. 5.
Fig. 5. Fluorine contents in pine needles as a function of their year of growth. Anomalous accumulation in the sites PRO, CIT and SAS are highlighted.
Fig. 6. Total (FTOT), acid oxalate extractable (FOX) and water extractable (FH2O) fluorine contents in the grain-size classes of three Etnean topsoils. Samples 31 and 35 were collected downwind from the summit craters, while sample 48 was collected upwind.
Fig. 7. Depth-profiles of total (FTOT), acid oxalate extractable (FOX) and water extractable (FH2O) fluorine contents in five soils. In the bottom right graph, FH2O of all profiles are plotted together with an enlarged scale.
Fig. 8. Time variations of deposition fluxes at Etna compared with estimated HF fluxes from the summit craters (see text). All data in Mg/day. The mass percentages (%) of plume-derived fluorine deposited on Etna's flanks is also shown.
Fig. 9. F adsorption efficiency of two soil profiles as a function of time. The starting solution is a natural rainwater sample with initial fluorine content of 3.8 mg/l.
Table 1.
Fluorine concentrations in ash leachates and deposition data
km = distance from the 2550 m vent of the July–August 2001 lateral eruption; ash dep. = total ash deposition; total F dep. = total leachable fluorine deposition (bulk sample); leachable fluorine analysis performed on separate grain-size classes (Φ = -log2 grain size in mm) are also reported. n.s. = no sample.
Table 2.
Fluorine contents in chestnut leaves and in pine needles collected in the Etnean area
Concentrations are expressed as µg/g of dry weight; km = distance from the summit craters; sites upwind from the summit crater are in italics. Pine samples collected in 2003 are subdivided into years of growth.
Table 3.
Fluorine contents in the Etnean soils
FH2O = fluorine extracted using distilled water; FOX = fluorine extracted using acid oxalate; FTOT = total fluorine content; km = distance from summit craters; sites upwind from the summit crater are in italics; Φ = log2 grain size in mm.
Corresponding author. Dipartimento CFTA, Università di Palermo, via Archirafi 36, 90123 Palermo, Italy. Tel.: +39 091 6849409; fax: +39 091 6849449.
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