There are a number of research articles and case studies that
review the adverse effects of HF in humans. The caustic and
corrosive nature of HF, coupled with its chemistry, comes to play
upon exposure [89]. Due to low dissociation constant of HF, it
penetrates tissue more quickly than typical inorganic acids [90]. As
a result, poisoning can readily occur through exposure of skin or
eyes, or when inhaled or swallowed [91]. Inhaling the HF vapours
(odour threshold is 0.042 mg/L) can cause ulcerative tracheobronchitis,
hemorrhagic pulmonary oedema, hypocalcaemia (lack of
enough calcium), hypomagnesaemia (lack of enough magnesium)
[91,92]. The lowest lethal limit for a 5-min exposure to HF is
estimated between 50 and 250 mg/L [93]. Depending on the
concentration of HF, symptoms of such exposure may not be
immediately evident as it gradually interferes with nerve function.
Delayed treatment increases the extent and seriousness of the
injury [94].
At present, it is still uncertain which ionized species of HF (F,
H2F+, or HF2
) is the most dangerous to humans as the literature
lacks a thorough study of the comparative toxicity of F, H2F+,
and HF2
. This is likely due to the difficult nature of studying the
chemistry of HF. However, the combined damaging effects of H+
and F in the human body are well documented. For example, HF
causes tissue damage by two different mechanisms [95]. Upon
exposure, concentrated HF (high H+ concentration) will immediately
lead to corrosive burns similar to those caused by burns
from strong acids. Secondly, the F being very lipophilic will
penetrate the outermost layer of the epidermis and deep into the
inner tissues [95] leading to painful necrosis, a characteristic of
focal bacterial or fungal infections (liquefactive necrosis) [96,97].
The H+ then separates from the F and attaches itself onto the
enzymes that balance the pH which stabilizes tissues [94]. The H+
damages the exterior surface of the cells in the body, whereas F
destroys the interior cell. Fluoride ions bind with biologically
important Ca2+ and Mg2+ in the body (Equations (12) and (13)),
destroying cell membranes and nerves on their way to the bone
[94,97,98]. Due to nerve damage, numbness renders the injured
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