Abstract:

Fluorosis is a widespread disease related to ingestion of high levels of fluorine through water and food. Although sometimes of anthropogenic origin, high levels of fluorine are generally related to natural sources. One of the main sources is represented by volcanic activity, which releases magmatic fluorine generally as hydrogen fluorine through volcanic degassing. For example, Mt. Etna in Italy is considered the greatest point source at the global scale, releasing on average 70 Gg of HF each year. But the impact of fluorine on human health is highly dependent on its chemical state, which means that high rates of release not necessary point to high impacts. The major pathway of magmatic fluorine to humans is in the form of fluoride ion (F-), through consumption of contaminated vegetables and drinking water. Contamination can happen either through direct uptake of gaseous HF or through rainwaters and volcanic ashes. Furthermore hydrogen fluoride, being one of the most soluble gases in magmas, exsolves only partially (< 20%) during volcanic activity. Volcanic rocks thus contain high levels of fluorine, which are transferred to groundwaters through water-rock interaction processes in the aquifers. Large magmatic provinces, like for example the East African Rift Valley, are therefore endemic for fluorosis. Finally a literature review of volcanic related fluorosis is given.

Excerpts:

Volcanoes represent the main natural persistent source of fluorine [6,7]. Fluorine is emitted by volcanoes mostly in the form of HF(g) [6], but emissions also contain much lower amounts of gaseous NH4F, SiF4, (NH4)2SiF6, NaSiF6, K2SiF6, KBF4 and organo-fluorides [4,8,9]. Volcanic emissions of fluorine take the form of either sluggish permanent release from quiescent volcanoes (passive degassing) or rarer but more impacting discharges during short-lived volcanic eruptions. Estimates of the global volcanogenic fluorine flux range 50 to 8600 Gg/a [6,7,10], with the former figure being probably an underestimate. Total anthropogenic emissions are in the same order of magnitude with the highest emissions are due to chlorofluorocarbon production (300 Gg/a) and coal burning (200 Gg/a) [5].

It has been estimated that passive degassing, like that existing at Mt. Etna (Italy) and Masaya (Nicaragua) volcanoes, accounts for about 90% of the volcanic fluorine release. In particular Mt. Etna is the largest known point source of atmospheric fluorine, contributing for about 70 Gg/a [11], even stronger than today’s total estimated anthropogenic release over Western Europe [12]. The influence of these emissions on the surrounding environment and in particular on vegetation has been investigated by several authors [12, 13, 14].

… Consequences on livestock are due either to direct ingestion of F-rich ashes deposited on the grass or to grazing of grass or drinking water that are F-contaminated. The problem is widespread in Iceland were the magmas are particularly F-rich. Since its settling in 9th century many eruptions on Iceland were responsible of F-poisoning of livestock. The first account of this problem was made after the 1693 eruption of Mt. Hekla by the farmer Eiriksson and the clergyman Petursson, which described the deformed teeth in sheep, cattle and horse calling them “ash-teeth” [21]. Death due to F-poisoning of livestock caused serious famines among Icelanders who were totally dependent on them. The worst episode followed the Laki eruption in 1783 causing the death of half of the population of Iceland [21]. Chronic fluorosis on grazing animals was also related to passive degassing (Ambrym, Vanuatu [22]) and to geothermal activity in recent volcanic areas Yellostone, U.S.A. [23]).

… The problem of fluorosis related to volcanic activity was first recognised in Japan were this pathology was called “Aso volcano disease” [27] due to the fact that fluorosis was widespread in the population living at the foot of this volcano…

References for excerpts:

[4] Weinstein LH, Davison A. 2003. Fluoride in the Environment, CABI Publishing.

[5] WHO. 2002. Fluorides. Geneva, World Health Organization. Environmental Health Criteria 227, pp. 268.

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[7] Halmer MM, Schmincke HU, Graf HF. 2002. The annual volcanic gas input into the atmosphere, in particular into the stratosphere: a global data set for the past 100 years, J. Volcanol. Geoth. Res., 115, 511-28.

[8] Francis P, Chaffin C, Maciejewski A, Oppenheimer C. 1996. Remote determination of SiF4 in volcanic plumes: A new tool for volcano monitoring, Geophys. Res. Lett., 23(3), 249-52, 1996.

[9] Schwandner FM, Seward TM, Gize AP, et al. 2004. Diffuse emission of organic trace gases from the flank and the crater of a quiescent active volcano (Vulcano, Aeolian Islands, Italy), J. Geophys. Res., 109, D04301.

[11] Francis P, Burton MR, Oppenheimer C. 1998. Remote measurements of volcanic gas compositions by solar occultation spectroscopy, Nature, 396, 567-70.

[12] Aiuppa A, Bellomo S, Brusca L, et al. 2006. Major ion bulk deposition around an active volcano (Mt. Etna, Italy), Bull. Volcanol., 68, 255-65.

[13] Garrec JP, Plebin R, Faivre-Pierret RX. 1984. The Influence of volcanic fluoride emissions on surrounding vegetation, Fluoride, 10, 152-6.

[14] Notcutt G, Davies F. 1989. Accumulation of volcanogenic fluoride by vegetation: Mt. Etna, Sicily, J. Volcanol. Geotherm. Res., 39, 329-33.

[21] Fridriksson S. 1983. Fluoride problems following volcanic eruption, In: Shupe, J.L., Peterson, H.B., Leone, N.C., (Eds.) Fluorides, – Effect on vegetation, animals and humans, Pearagon Press, UT, 339-44.

[22] Crimp R, Cronin S, Charley D, et al. 2006. Dental fluorosis attributed to volcanic degassing on Ambrym, Vanuatu, Cities on Volcanoes 4, Quito, Ecuador, 23-7 Jannuary 2006, Abstract book.

[23] Garrot RA, Eberhardt LL, Otton JK, et al. 2002. A geochemical trophic cascade in Yellowstone’s geothermal environments, Ecosystems, 5, 659-66.

[27] Kawahara S. 1971. Odontological observations of Mt. Aso-volcano disease, Fluoride, 4, 172-5.

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