Hydrogen fluoride

CHEMICAL SUBSTANCE IDENTIFICATION

Chemical name                 

Hydrogen fluoride

Synonyms                           

hydrofluoric acid [1], Fluorhydric acid, fluorine, Hydrogen fluoride, anhydrous [2]

IUPAC name

hydrogen fluoride [1]

CAS No

7664-39-3

REACH registration number

EC No

Molecular formula              

FH or HF [1,2]

Substance group/chemical family

Mono constituent substance/ Inorganic [1]

Appearance

Physical state

Odour

Form

Colour

Gaseous (100%) [1], fuming liquid or gas [2]

strong, irritating odour [2]

Liquified gas (100%) [1]

colourless

USES AND HANDLING ISSUES

Relevant identified uses

This substance is used in the following products: metal surface treatment products, washing & cleaning products, non-metal-surface treatment products, extraction agents, pH regulators and water treatment products and laboratory chemicals. This substance has an industrial use resulting in manufacture of another substance (use of intermediates).

This substance is used in the following areas: mining. This substance is used for the manufacture of: chemicals, metals and fabricated metal products.

This substance is used in the following activities or processes at workplace: transfer of chemicals at dedicated facilities, transfer of substance into small containers, closed processes with no likelihood of exposure, closed batch processing in synthesis or formulation, closed, continuous processes with occasional controlled exposure, batch processing in synthesis or formulation with opportunity for exposure and treatment of articles by dipping and pouring. [1]

Hydrogen fluoride is used primarily to produce aluminum fluoride, synthetic cryolite, fluoropolymers, and chlorofluorocarbons. It is also used in inorganic fluoride production, uranium enrichment, and fluorine production. Fluoride is found in some foods and beverages, particularly fish, seafood, gelatin, and tea; and many public water sources are fluoridated. [3]

Handling considerations

ECHA has no data from registration dossiers on the precautionary measures for using this substance. [1]

Store cool. Well closed. Fireproof if in building. Ventilation along the floor. Separated from food and feedstuffs and incompatible materials. Store in an area without drain or sewer access. See Chemical Dangers. Containers which are opened must be carefully resealed and kept upright to prevent leakage. Store in corrosive resistant polyethylene container with a resistant inner liner. Do not store in glass Storage. [2]

Skin: If chemical is in liquid form, wear appropriate personal protective clothing to prevent skin contact. Eyes: If chemical is in liquid form, wear appropriate eye protection to prevent eye contact. Wash skin: If the chemical is in liquid form, the worker should immediately wash the skin when it becomes contaminated. [2]

PHYSICO-CHEMICAL PROPERTIES

Molecular weight                                  

20.0064 g/mol [2]

Bulk density/Specific gravity

 0.97 (Relative density at 20°C) [1]

pH

In water a weak acid [2]

Hydrofluoric acid or HF is an extremely corrosive acid. However, it is a weak acid  because it does not completely dissociate in water. The ions it forms upon dissociation are too strongly bound to each other for it to act as a strong acid. [5]

pH varies versus HF concentration. Below a pH of 3.2 the dominant species are the fully protonated HF^o and H₂F₂^o. These dissociate to F^- and HF₂^- and above pH of 3.2 F- is the dominant species. The weak acid behavior of hydrofluoric acid tends to buffer the pH so that concentrated solutions have a pH between 0.5 and 1. [6]

Particle size

EC

Melting/Freezing point

-84.01 °C  at 101 325 Pa [1]

Boiling point

19.35 °C at 101 325 Pa [1]

Flash point

[2]

Flammability

Non flammable (100%) [1]

Vapour density

Vapour pressure

122 kPa @ 24.85 °C [1]

Solubility in water

Very soluble in water [2]

Solubility in organic solvents

Very soluble in alcohol, slightly soluble in ether, soluble in many organic solvents [2]

Solubility in inorganic solvents

Hydrolysis

Ionicity in water

Surface tension

10.2 mN/m at 0 °C [2]

Dispersion properties

Explosiveness

Non-explosive (100%) [1]

Other properties

Non oxidising (100%) [1]

Dynamic viscosity at 20 °C: 0.256 mPa.s [1]

When heated to decomposition it emits highly corrosive fumes [2]

The gas is heavier than air. The vapour is heavier than air. [2]

Stability and reactivity

Chemical stability

Stable under recommended storage conditions. [2]

Reactivity hazards

Water-Reactive, Air-Reactive [2]

Corrosivity

Corrosive, dissolves silica, silicic acid, glass [2]

Polimerization

Incompatibility with various substances

Metals, Alkali metals, Strong bases, glass [2]

Special remarks on reactivity

Physical, chemical and biological coefficient

Koc

0.23 (estimated) [2]

Kow

pKa

 3.19 at 20 °C [1, 2] 

log Kp

Henry-constant

ENVIRONMENTAL FATE AND BEHAVIOUR

Artificial pollution sources

HF may enter the environemnt from both natural (volcanos, weathering of minerals and marine aerosols) and antropogenic  sources. The latter includes the production of HF itself and as by-product during other production processes (phosphate fertiliser, aluminum and steel production). Once released into the environment HF is unlikely to remain in its original form for very long. In air, water and soil HF is transformed into a variety of  other F-compounds. [7]

Hydrogen fluoride's use in the production of refrigerants, solvents and aerosols as well use as a chemical reagent, catalyst, in chemical manufacture, additive in rocket propellants and in refining of uranium may result in its release to the environment through various waste streams. Electrical utilities are the largest source of hydrogen fluoride emissions to air in the US. [2]

General terrestrial fate

Besides naturally occurring fluoride, F may enter the terrestrial environment via atmospheric deposition, fluoride containing sludge or phosphate fertilisers. In soils (pH<6) fluor is found predominantly in bound form in fluoride containing minerals as feldspar, cryolite, apatite and clay minerals. Therefore fluoride is immobile in soils, but leaching to the B horizon is possible in soils with low clay content. Fluoride has strong complex forming properties, confirmed by the incrase of Al and Fe concentrations with the increase of F concentrations in pore water or groundwater. At above pH>6 the fluoride ion is the dominant species. [7]

General aquatic fate

HF (F) enters the aquatic environment via industrial waste-water, atmospheric deposition or runoff from fertilisers or F-contaning sludge. In freshwater at pH above 5 the free ion is the main fluride species. At lower pH the proportion of the fluoride ion decreases while HF₂^- and non-dissociated HF increase. In the presence of phosphate insoluble fluorapatite is formed, a large part of which is transferred to the bottom of sediments. [7]

General atmospheric fate

Fluorides are emitted to the atmosphere as gaseous compounds (75%) or as solids in the form of aerosols (25%). Gasous fluorides in the atmosphere are predominantly HF (and SiF4). HF is removed relatively rapidly form the atmosphere by wet and dry deposition, with a half-life of cca. 12hrs and 14hrs, repectively. Fluoride aerosol is eliminated slowly predominantly (65%) by wet deposition with a half-life of 50 hours. For dry deposition of fluoride aerosol a half-life of 12 days is reported. [7]

General persistence and degradability

Abiotic degradation and metabolites

Biodegradation and metabolites

Bioconcentration

In freshwater aquatic organisms fluoride accumulates  primarily in the exoskeleton of crustacea and in the bones of fish. No F accumuation was found in edible tissues. In an experimental marine ecosystem with fish, crustacea and plants , F was found to accumulate in all species [7]

Earthworms from contaminated sites reflected F-contamination since F content in earthworms reached 135 mg/kg (without gut) whereas worms from unpolluted sites showed F contents of 6-14 mg/kg. Fluoride uptake by plants in soil is also possible but the bioavailability of fluoride in soil is usually low. The most important F exposure route for plants is uptake from the atmosphere. [7]

Volatilization

Photolysis

Hydrolysis

Soil adsorption and mobility

ENVIRONMENTAL CONCENTRATIONS

Measured data

Volcanoes are the major natural source of hydrogen fluoride emissions to air, ranging from 0.6 to 6 million metric tons per year. The ambient air concentrations of gaseous fluorides in Canada and the US are reported to range from 0.01 to 1.65 ug/m3; approximately 75% of which exists as hydrogen fluoride [2]

The concentration of fluoride in natural waters depends on geological, physical and chemical characteristics  at the location. In surface waters that are not influenced by F-containing rock formations the natural F-concentrations range between 0.01-0.3 mg/L. In surface waters influenced by F-containing formations the F levels may reach >20 mg/l.  [7]

The mean fluoride content of mineral soils is 200-300 mg/kg, whereas that of organic soils is usually lower. The F-concetration usually incrases with the soil depth. [7]

Fluoride content in groundwater depends on many factors, such as geological, physical, chemical characteristics of the water-suppying area, the temperature, the consistency of the soil, the pH, the depth of the well, etc. In the USA fluoride levels in groundwater range  between 0.02-1.5 mg/l. [7]

ECOTOXICOLOGICAL INFORMATION

General adverse effects on ecosystem

Acute toxicity (LC50, EC50)

Aquatic systems

All reported tests with aquatic organisms were performed with  NaF. Because HF occurs in the aquatic compartment mainly as fluoride ion, NaF tests can be used for the evaluation of HF effects in aquatic organisms. All reported test results were corrected for the fluoride ion. [7]

LC50: 51 mg/L (freshwater fish, 4 days) [1]

EC50 / LC50: 26 mg/L (freshwater invertebrates) [1]

EC50 / LC50: 10.5 mg/L (marine invertebrates) [1]

EC50: 43 mg/L (freshwater algae) [1]

EC50: 81 mg/L (marine water algae) [1]

Terrestrial systems

All test results are based on the fluoride ion [7]

LD50 (24 h) 17 - 50 mg/kg bw (birds) [1]

Chronic toxicity (NOEC, LOEC)

Aquatic systems

All reported tests with aquatic organisms were performed with  NaF. Because HF occurs in the aquatic compartment mainly as fluoride ion, NaF tests can be used for the evaluation of HF effects in aquatic organisms. All reported test results were corrected for the fluoride ion. [7]

EC10 / LC10 or NOEC: 4 mg/L (freshwater fish, 22 days) [1]

EC10 / LC10 or NOEC: 8.9 mg/L (freshwater invertebrates) [1]

EC10 or NOEC: 50 mg/L (freshwater algae) [1]

EC10 or NOEC: 50 mg/L (marine water algae) [1]

EC10 or NOEC: 510 mg/L (microorganisms) [1]

Terrestrial systems

All test results are based on the fluoride ion. [7]

EC10 / LC10 / NOEC: 1200 mg/kg soil dw (terrestrial macroorganisms except arthropods,  5.133 months) [1]

EC10 / NOEC: 106 mg/kg soil dw (soil microorganisms, 63 days) [1]

HUMAN HEALTH EFFECTS and PROTECTION

Routes of human exposures

inhalation, skin absorption (liquid), ingestion (solution), skin and/or eye contact [2]

At room temperature HF is a liquid gas and therefore, inhalation and dermal contact are the main routes of exposure for the human population. Oral exposure to fluoride occurs indirectly via the environment, via driniking water and food. [7]

General effects

irritation eyes, skin, nose, throat; pulmonary edema; eye, skin burns; rhinitis; bronchitis; bone changes [2]

Endocrine disruption

Mutagenicity

The evidence of genotoxicity of fluoride was inconsistent. Fluoride does not appear to be a direct mutagen, but a number of mammalian in vitro systems have shown dose-dependent cytogenetic or cell-transformational effects of fluoride exposure. [3]

In nonfatal cases of acute hydrofluoric acid poisoning, urinary and serum fluoride concentrations as high as 110 and 42 mg/L, respectively, have been reported. [3]

Carcinogenicity

Not listed [2]

The U.S. Environmental Protection Agency has not classified fluoride with respect to carcinogenicity . The International Agency for Research on Cancer lists inorganic fluorides in group 3, "not classifiable as to its carcinogenicity to humans," on the basis of reviews in 1982 and 1987. [3]

Reprotoxicity

Teratogenicity

Skin, eye and respiratory irritations

Skin: Adverse effect observed (corrosive) [1]

Eye: Adverse effect observed (irritating) [1]

Skin sensitisation: No adverse effect observed (not sensitising) [1]

Metabolism:

absorption, distribution & excretion

Exposure limits

DNEL: 1.5 mg/m³ (workers, inhalation, long term, systemic effects, repeated dose toxicity) [1

DNEL:  2.5 mg/m³ (workers, inhalation, acute/short term, systemic effects, irritation (respiratory tract)) [1]

DNEL: 1.5 mg/m³ (workers, inhalation, long term, local effects, repeated dose toxicity) [1

DNEL:  2.5 mg/m³ (workers, inhalation, acute/short term, local effects, irritation (respiratory tract)) [1]

DNEL: 30 µg/m³ (general population, inhalation, long term, systemic effects, repeated dose toxicity) [1]

DNEL:  30 µg/m³ (general population, inhalation, acute/short term, systemic effects, repeated dose toxicity) [1]

DNEL: 200 µg/m³ (general population, inhalation, long term, local effects, irritation (respiratory tract) [1]

DNEL:  1.25 mg/m³ (general population, inhalation, acute/short term, local effects, irritation (respiratory tract) [1]

DNEL: 10 µg/kg bw/day (general population, oral, long term, systemic effects, repeated dose toxicity) [1]

DNEL:  10 µg/kg bw/day (general population, oral, acute/short term, systemic effects, repeated dose toxicity [1]

Drinking water MAC

Other information

Fluoride is an oxidative stress, immune system and apoptosis inducer in the animal as well as in human system. [4]

Animal toxicity data

Acute toxicity (LD50)

LC50 (60 min) 1 307 - 2 340 mg/kg (rat, inhalation) [1]

LC50 (30 min) 2 042 - 2 300 ppm (rat, inhalation) [1]

LC50 (15 min) 2 689 ppm (rat, inhalation) [1]

LC50 (5 min) 4 970 - 18 200 ppm (rat, inhalation) [1]

very toxic

Chronic toxicity (NOEL, LOEL)

NOAEL (rat): 100 ppm (oral, repeated dose toxicity) [1]

NOEL (rat): 30 - 200 ppm, (oral, repeated dose toxicity) [1]

NOEL (mouse): 50 - 400 ppm, (oral, repeated dose toxicity) [1]

LOEL (mouse): 50 ppm, (oral, repeated dose toxicity) [1]

NOAEL (rat): 1 ppm (inhalation) [1]

ENVIRONMENTAL STANDARDS AND REGULATIONS

Danger! According to the classification provided by companies to ECHA in REACH registrations this substance is fatal if swallowed, is fatal in contact with skin, is fatal if inhaled and causes severe skin burns and eye damage.

Additionally, the classification provided by companies to ECHA in CLP notifications identifies that this substance causes serious eye damage.[1]

According to REACH registrations:

H300: Fatal if swallowed.  H314: Causes severe skin burns and eye damage. H310: Fatal in contact with skin. H330: Fatal if inhaled. [1]

According to CLP notifications:

H300: Fatal if swallowed.  H314: Causes severe skin burns and eye damage. H310: Fatal in contact with skin. H330: Fatal if inhaled. H318: Causes serious eye damage. H335: May cause respiratory irritation. [1]

EINECS regulation

̵listed on EINECS (European INventory of Existing Commercial chemical Substances) List [1]

OSHA regulations etc.

OTHER INFORMATION, SPECIAL REMARKS

Classification and proposed labelling with regard to toxicological data

CREATED, LAST UPDATE

Created

2019. 12. 10

Last update

2020. 09. 24

REFERENCES

[1] ECHA, Hydrogen fluoride, https://echa.europa.eu/hu/brief-profile/-/briefprofile/100.028.759, Accessed 2019. 12. 10

[2] Pubchem, Hydrofluoric acid, https://pubchem.ncbi.nlm.nih.gov/compound/Hydrofluoric-acid, Accessed 2019. 12. 11

[3] National Research Council (US) Committee on Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants. Emergency and Continuous Exposure Guidance Levels for Selected Submarine Contaminants: Volume 3. Washington (DC): National Academies Press (US); 2009. 4, Hydrogen Fluoride. Available from: https://www.ncbi.nlm.nih.gov/books/NBK219903/, Accessed 2020. 09. 23

[4] Arup Giri, Vijay K Bharti*, Kunzes Angmo, Sahil Kalia, Bhuvnesh Kumar (2016) Fluoride induced oxidative stress, immune system and apoptosis in animals: a review, International Journal of Bioassays 5.12 (2016): 5163-5173, http://dx.doi.org/10.21746/ijbio.2016.12.0011

[5] Helmenstine, Anne Marie, Ph.D. "Is HF (Hydrofluoric Acid) a Strong Acid or a Weak Acid?" ThoughtCo, Aug. 27, 2020, thoughtco.com/is-hydrofluoric-acid-a-strong-or-weak-acid-603636. Accessed 2020. 09. 23

[6] Denham, M. & Millings, M. (2003) Geochemistry of Hydrofluoric Acid in Kaolinitic Soils, WSRC-TR-2003 00517. https://www.researchgate.net/figure/pH-versus-concentration-of-hydrofluoric-acid_fig2_267558087 Accessed 2020. 09. 24

[7] EC JRC EUR 19729 (2001) European Union Risk Assessment Report, Hydrogen Fluoride, ISBN: 92-894-0485-x. https://echa.europa.eu/documents/10162/be5a5363-654a-4efd-beae-1abdf730245b Accessed 2020. 09. 24