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Hydrogen Fluoride (HF)

There are no documented examples of gaseous volcanic HF at high concentrations in locations where it would have an adverse effect on people's health. However, during explosive eruptions HF and fluoride can condense onto ash and tephra particles in the plume, forming an outer layer of adsorbed fluorine on the particles. Smaller particles have a larger surface area, so can adsorb more fluorine per unit mass than larger particles (Okarsson, 1980). These smaller particles are carried further from the volcanic source, so their greater fluorine-carrying capacity extends the zone of potential fluorine poisoning considerably. Since the fluorine is highly soluble in water, it is quickly introduced into watercourses if the ash encounters wet ground or rain (Gregory, 1996). To address this additional hazard, guideline levels for fluoride in drinking water are presented here along with those for atmospheric HF.

Exposure Effects
Existing Guidelines
Effects on Grazing Animals
Volcanic Examples and Incidents
Volcanic Gases and Aerosols Index


Hydrogen fluoride (HF) is a colourless gas with a strong irritating odour. It is soluble in all proportions in water (Gangolli, 1999) and is non-flammable. Hydrogen fluoride gas has a sour taste and reacts in moist air to form a mist. The gas is 30% less dense than air (0.82 g L-1 at 25° and 1 atm (Lide, 2003)). Typical concentrations of HF in dilute volcanic plumes are <1 ppm, and the tropospheric background level is very low (Brimblecombe, 1996; Oppenheimer et al., 1998).

Exposure Effects

Absorption of fluoride from gas exposure is mainly through the respiratory tract. Its high water solubility means that absorption in the nose and upper respiratory tract is rapid. Vapours of hydrogen fluoride are a severe irritant to the eyes, mucous membranes and the upper respiratory tract and inhalation may cause ulcers of the upper respiratory tract. Short-term overexposure causes extreme irritation and burning of the skin and mucus membranes. Repeated or prolonged exposure to lower concentrations may cause changes in the bones as well as chronic irritation of the nose, throat, and lungs (NIOSH, 1981). Concentration thresholds for health effects are outlined in the table.

Health effects of respiratory exposure to hydrogen fluoride gas
(Baxter, 2000; NIOSH, 1981; Sax and Lewis, 1989)

Exposure Limits (ppm) Health Effects
<3 Irritation of nose and eyes
3< Pronounced eye and respiratory symptoms, including burning throat and cough after 1 hour
30 Respiratory symptoms worsen. Can be tolerated for several minutes
50-250 Dangerous even for brief exposure
120 Maximum concentration in air that can be tolerated for 1 minute. Smarting of the skin, conjunctivitis and irritation of the respiratory tract occur

Deposition of volcanic HF into drinking water poses a serious threat in the form of fluorosis. Thresholds for concentrations of fluoride in water are outlined in the table below.

Health effects of ingesting fluoride via drinking water
(after Kaminsky et al., 1990)

(mg L-1)
Health Effects Population affected (%)
1 Dental Fluorosis 1-2
2 Dental Fluorosis 10
2.4-4.1 Dental Fluorosis 33
8 Osteosclerosis (on x-ray) -
>10 Skeletal Fluorosis -

Existing Guidelines

Only occupational guidelines exist for exposure to gaseous HF. A greater hazard is posed by the deposition of volcanic HF on ash and tephra and the subsequent introduction of fluoride into water supplies (see tables below). Application of the fluoride drinking water guideline values must take into account the local climatic conditions and any consequent increases in water consumption levels.

Occupational Guidelines for HF Gas

Country/ Institution Level (ppm) Level µg m-3 Averaging Period Guideline Type Date of Implem- 
Relevant Law Notes Ref.
EU - 2500 8 hour TWA Occupational Exposure Limit (OEL)   Adopted recomm-
1 830 STEL OEL   Adopted recomm- 
UK 3 2500 15 min MEL   New, IOELV   b
1.8 1500 8 hour TWA MEL   New, IOELV   b
USA 6 5000 15 min ceiling REL 2003 NIOSH   c
3 2500 8 hour TWA PEL   OSHA Regulations (Standards - 29 CFR) 1 d
3 2500 10 hour TWA REL 2003 NIOSH   c
2   10 min ERPG-1 1999 Emergency Response Planning Guideline   e
50   10 min ERPG-2 1999 Emergency Response Planning Guideline   e
170   10 min ERPG-3 1999 Emergency Response Planning Guideline   e
2   1 hour ERPG-1 1997 Emergency Response Planning Guideline   e
20   1 hour ERPG-2 1997 Emergency Response Planning Guideline   e
50   1 hour ERPG-3 1997 Emergency Response Planning Guideline   e
  1. ppm by volume at 25ºC and 760 torr.
  1. http://europa.eu.int/comm/employment_social/health_safety/docs/oels_en.pdf
  2. HSE, 2002. Occupational Exposure Limits 2002. HSE Books, Sudbury.
  3. NIOSH Pocket Guide to Chemical Hazards (NPG). http://www.cdc.gov/niosh/npg/npg.html
  4. OSHA Standards Website
  5. AIHA Emergency Response Planning Guidelines Committee, 2002. Emergency Response Planning Guidelines 2002 Complete Set, American Industrial Hygiene Association, Fairfax.

Drinking water tolerance levels for fluoride

Country/ Institution Level
(mg L-1)
Date of Implemen- 
Relevant Law Notes Ref.
UK 1.5 2000 Water Supply (Water Quality) Regulations SI No. 3184   a
WHO 1.5 1984   1 b
USA 4 2004 EPA 822-R-04-005 2 c
  1. Based on a consumption of 2 L water per day. Higher concentrations may give rise to dental fluorosis in some children.
  2. This is the maximum contaminant level and is currently under review. The non-enforceable secondary drinking water regulation for the prevention of cosmetic or aesthetic effects is 2 mg L-1.
  1. http://www.dwi.gov.uk/regs/si3184/3184.htm
  2. WHO, 2004. Guidelines for drinking-water quality, 3rd edn. World Health Organisation. Geneva, and http://www.who.int/water_sanitation_health/dwq/gdwq3/en/
  3. EPA 2004 Edition of the drinking water standards and health advisories, http://www.epa.gov/waterscience/drinking/

Effects on Grazing Animals

Poisoning in sheep is likely to occur where the fluorine content of dried grass exceeds 250 ppm. The most dangerous situations for grazing animals are usually some distance from the erupting volcano where the ash or tephra layer is so thin that it does not deter grazing. Poisoning can occur in regions where only a 0.5 mm thick layer of ash or tephra has deposited. Acute poisoning can be accompanied by depression, salivation, loss of appetite and co-ordination, abnormal breathing, nasal secretions, convulsive seizures, pulmonary oedema, kidney and liver damage, blindness, coma and death (O'Hara et al., 1982).

Volcanic Examples and Incidents

Measurements of fluxes of HF are much more common than concentrations and we have not been able to find any reports confirming direct impacts of high concentrations of gaseous HF on people. In general, it appears that levels of primary volcanic HF at degassing volcanoes are rarely hazardous, although the contamination of drinking water and soils by fluoride as a secondary effect is well documented.

  • Popocatepetl, Mexico: Near-vent concentrations of HF in February 1997 were ~0.3 ppm (250 µg m-3) (Goff et al., 1998), well below occupational guidelines.
  • Masaya, Nicaragua: Maximum concentrations in the plume at the rim of Santiago crater in May 2001 were 0.567 ppm (448 µg m-3) (Allen et al., 2002), again well below occupational guidelines, however, in March 1999, maximum plume concentrations averaged over the Masaya crater were >4 ppm (Horrocks et al., 1999), exceeding many short- and long- term exposure guidelines.
  • Kilauea Volcano, Hawaii: Measurements of HF in plumes formed by the interaction of lava and sea water in March 1990 were below guidelines at <1 ppm (Kullman et al., 1994), but measurements at the Pu`u `O`o eruptive vent in 2004 yielded HF concentrations ranging from ~3-15 ppm, well above most exposure limits (USGS, Hawaiian Volcano Observatory, unpublished data).

Impacts on animals from consuming effected vegetation and ash mixed with soil have frequently been reported, as have impacts on humans from consuming contaminated drinking water.

  • Nyiragongo, DR Congo: In 2003 water tanks collecting rainwater in several localities downwind of Nyiragongo were found to have fluoride concentrations up to 23 mg L-1, 15 times greater than the WHO guideline.
  • Lonquimay, Chile: During the 1988 activity, 100,000 farms animals were affected by fluoride contaminated ash and thousands of people suffered from health effects associated with high concentrations of fine ash (seeParticulate Matter (PM) and Aerosol) that may have been coated in fluoride (SEAN 14:6-7). Most of these people were subsequently evacuated.
  • Etna, Italy; Kilauea, Hawaii; La Soufriere, Guadeloupe: High levels of fluoride have been found in vegetation at these volcanoes (Garrec et al., 1977; Notcutt and Davies, 1989; Notcutt and Davies, 1993).
  • Furnas Caldera, Azores: High fluoride levels in lichen suggest that volcanic emissions may be responsible for high ground water F levels, which have caused dental fluorosis in the local population (Notcutt and Davies, 1999).
  • Hekla, Iceland: Following the 1970 eruption, a combination of a poor hay crop and fluorosis from fluoride adsorbed on ash caused the deaths of 3% of adult sheep and 8-9% of lambs in areas where there was as little as 1 mm thickness of tephra (Thorarinsson and Sigvaldason, 1972, O'Hara, et al., 1982).
  • Ruapehu, New Zealand: The deaths of several thousand sheep following the 1995 eruption are thought to be have been due to fluorosis and isolated cases of fluorosis in cattle were reported following both the 1995 and 1996 eruptions (Cronin et al., 2003).
  • Laki Craters, Iceland: Following the 1783-1784 eruption, fluorosis is believed to have accounted for a high proportion of the livestock deaths on the island (11,500 cattle, 28,000 horses and 190,000 sheep) (Gregory, 1996).


Allen, A.G., Oppenheimer, C., Ferm, M., Baxter, P.J., Horrocks, L.A., Galle, B., McGonigle, A.J.S. and Duffell, H.J., 2002. Primary sulfate aerosol and associated emissions from Masaya Volcano, Nicaragua. Journal of Geophysical Research, 107(D23).

Brimblecombe, P., 1996. Air Composition and Chemistry. Cambridge University Press, Cambridge.

Cronin, S.J., Neall, V.E., Lecointre, J.A., Hedley, M.J. and Loganathan, P., 2003. Environmental hazards of fluoride in volcanic ash: a case study from Ruapehu volcano, New Zealand. Journal of Volcanology and Geothermal Research, 121(3-4): 271-291.

Gangolli, S. (Ed.), 1999. The Dictionary of Substances and their Effects, 2nd edn. The Royal Society of Chemistry. Cambridge.

Garrec, J.P., Lounowski, A. and Plebin, R., 1977. The influence of volcanic fluoride emissions on the surrounding vegetation. Fluoride, 10(4): 152-156.

Goff, F., Janik, C.J., Delgado, H., Werner, C., Counce, D., Stimac, J.A., Siebe, C., Love, S.P., Williams, S.N., Fischer, T. and Johnson, L., 1998. Geochemical surveillance of magmatic volatiles at Popocatpetl Volcano, Mexico. Geological Society of America Bulletin, 110(6): 695-710.

Gregory, N., 1996. Toxicity hazards arising from volcanic activity. Surveillance, 23(2): 14-15.

Kaminsky, L.S., Mahoney, M.C., Leach, J.F., Melius, J.M. and Miller, M.J., 1990. Fluoride: benefits and risks of exposure. Critical Reviews in Oral Biology and Medicine, 1: 261-281.

Kullman, G.J., Jones, W.G., Cornwell, R.J. and Parker, J.E., 1994. Characterization of air contaminants formed by the interaction of lava and sea water. Environmental Health Perspectives, 102(5): http://ehpnet1.niehs.nih.gov/docs/1994/102-5/kullman.html.

Lide, D.R. (Ed.), 2003. CRC Handbook of Chemistry and Physics, 84th edn. CRC Press. Boca Raton, Florida.

National Institute for Occupational Safety and Health (NIOSH), 1981. Occupational Health Guidelines for Chemical Hazards, DHHS (NIOSH) Publication No. 81-123. http://www.cdc.gov/niosh/81-123.html.

Notcutt, G. and Davies, F., 1989. Accumulation of volcanogenic fluoride by vegetation: Mt. Etna, Sicily. Journal of Volcanology and Geothermal Research, 39(4): 329-333.

Notcutt, G. and Davies, F., 1993. Dispersion of gaseous volcanogenic fluoride, island of Hawaii. Journal of Volcanology and Geothermal Research, 56: 125-131.

Notcutt, G. and Davies, F., 1999. Biomonitoring of volcanogenic fluoride, Furnas Caldera, Sao Miguel, Azores. Journal of Volcanology and Geothermal Research, 92(1-2): 209-214.

O'Hara, P.J., Fraser A.J., James M.P., 1982. Superphosphate poisoning in sheep: the role of fluoride. New Zealand Veterinary Journal, 30: 191-201.

Oppenheimer, C., Francis, P., Burton, M., Maciejewski, A.J.H. and Boardman, L., 1998. Remote measurement of volcanic gases by Fourier transform infrared spectroscopy. Applied Physics B, 67: 505-515.

Oskarsson, N., 1980. The interaction between volcanic gases and tephra: fluorine adhering to tephra of the 1970 Hekla eruption. Journal of Volcanology and Geothermal Research 8, 251-266.

Sax, N.I. and Lewis, R.J., Sr., 1989. Dangerous Properties of Industrial Materials, 7th edn. Van Nostrand Reinhold. New York.

Smithsonian Institution, 1989. Lonquimay. Scientific Event Alert Network (SEAN) Bulletin, v. 14, nos. 6-7.

Thorarinsson, S. and Sigvaldason, G.E., 1972. The Hekla eruption of 1970. Bulletin Volcanologique, 36(2): 269-288.