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f03:
Solubility and toxicity of different fluorides
Consumption of fluoride cannot be avoided.
It appears in so many different forms and in so many different environments
(in our water supplies, our food, the air we breath, etc.).
Therefore, it is important to know exactly
how toxic each type of fluoride is and how much is considered safe when
exposed to this chemical.
Toxicity is related to solubility. If a
compound of fluoride (fluorine + one or more other elements) is very
soluble, the fluoride ion is made more readily available.
In 1971, former Aston University chemist
Malcolm Harris investigated some fluoride compounds and determined the
following table of solubility (solubility: "... a critical aspect of
toxicity");-
| Calcium
fluoride |
natural |
Solubility =
16 ppm at 18ºc and 17 ppm at 26ºC |
| Sodium
Fluoride |
artificial |
42,200 ppm at
18ºC |
| Sodium
fluosilicate |
artificial |
6,520 ppm at
17ºC |
|
Hydrofluorosilic acid |
artificial |
miscible
liquid |
It can be clearly seen that sodium-fluoride
compounds are far more soluble than calcium fluoride. Hydrofluorosilic acid
(used to fluoridate water supplies in the UK and [extensively] in the USA)
is a "miscible" liquid. A miscible liquid means something which can be mixed
(in this instance, with water).
By definition, hydrofluorosilic acid has 6
atoms of fluorine (H2SiF6).
Of these six atoms, it is sometimes assumed that all six will become simple
fluoride ions. However, there is no known published to demonstrate thsi
actually happens. In fact, the best available knowledge suggests that only
four of these atoms will become fluoride ions and the remaining two will
form more 'exotic' complexes (depending on the quality of water the compound
is mixed with).
More information on solubility:
| Lanthanum Fluoride (LaF3) |
Insoluble
in water |
| Magnesium Fluoride (MgF2) |
0.0002g/100g water |
| Calcium Fluoride (CaF2) |
0.0017gm/100gm water at
20°C |
| Strontium Fluoride (SrF2) |
0.012g/100g water at 27°C |
| Barium Fluoride (BaF2) |
0.17g/100g water at 23°C |
| Lithium Fluoride (LiF) |
0.27g/100g water at 20°C |
| Sodium Fluoride (NaF) |
4.22g/100g water at 18°C |
Source:
www.crystran.co.uk
Considering that solubility is "... a
critical aspect of toxicity", it is now prudent to examine another table
which shows different types of fluoride. Professor Kaj Roholm's table of
toxicity gives three categories of inorganic fluorine compounds (it should
be noted that Prof. Roholm is the author of the first and most comprehensive
monograph on fluorine toxicity);-
|
EXTREMELY TOXIC |
VERY TOXIC (Easily soluble
fluorides and fluorosilicates) |
MODERATELY TOXIC (Poorly
soluble fluorides) |
| Hydrogen
Fluoride (anhydrous) |
Sodium
Fluoride |
Cryolite |
| Silicon
Tetrafluoride |
Potassium
Fluoride |
Calcium
Fluoride |
| Hydrofluoric
Acid |
Ammonium
Fluoride |
|
|
Hydrofluorosilicic Acid |
Sodium
Fluorosilicate |
|
| |
Potassium
Fluorosilicate |
|
| |
Ammonium
Fluorosilicate |
|
Hydrofluoric acid and hydrofluorosilicic
acid are classified as being extremely toxic. Hydrofluorosilicic acid is
used to fluoridate UK water supplies. The similarly dangerous hydrofluoric
acid carries the following warning issued by the Health & Safety Executive
(2001);-
Hydrofluoric acid poisoning
Recommendations on first aid procedures
Health & Safety Executive:
http://www.hse.gov.uk
Information contained within this document
is accurate as of 1/1/2001
IMPORTANT.
ALWAYS contact the HSE for advice. See
Disclaimer (below). This leaflet is aimed at employers and employees in
industries where hydrofluoric acid is used. It provides information on:
DISCLAIMER
[1] THE INFORMATION PROVIDED ON THIS
WEB-PAGE IS PURELY FOR THE PURPOSE OF HIGHLIGHTING THE DANGERS OF
HYDROFLUORIC ACID.
[2] ANYONE WHO WORKS WITH HYDROFLUORIC ACID
SHOULD ENSURE THAT THEIR EMPLOYER HAS THE APPROPRIATE MEASURES TO DEAL WITH
ANY INCIDENT RELATING TO THE USE OF THIS CHEMICAL.
Health Effects
Hydrofluoric acid is corrosive. It can
cause severe burns to the skin and eyes. If it comes into contact with skin,
you may not feel pain at once. Hydrofluoric acid is also highly irritating
to the respiratory system and very toxic if swallowed.
Precautions
The Control of Substances Hazardous to
Health Regulations 1999 (COSHH) apply. A COSHH assessment should be
completed. Consider the use of safer alternatives. If there are no suitable
alternatives, the assessment should detail appropriate precautions to be
taken when using hydrofluoric acid, which include using a safe system of
work. Employers should ensure that employees are given adequate information
and training on the hazards to health posed by hydrofluoric acid, and the
precautions to take to avoid them.
Employers should:
-
always use the protections provided;
-
always wash gloves and other impervious
clothing before removing them;
-
test gloves for pinholes using a method
advised by the manufacturers (this might be done by filling them with
water, before drying and putting them away for use again), discarding
gloves that are not sound;
-
always wash their hands before leaving
the work area
First aid:
-
Urgent action is required. Obtain
immediate medical attention.
-
When giving first aid, protect yourself
and the casualty from further exposure.
-
Casualties should be sent to hospital as
soon as possible (see opposite). In all cases, the hospital should be
informed of the cause of injury.
Skin contact
-
Remove contaminated clothing while
protecting your hands with suitable gloves.
-
Flood the skin with plenty of water for
at least 5-10 minutes.
-
Apply calcium gluconate gel on and
around the affected area and continuously massage into the skin for at
least 15 minutes after pain is relieved. Cover the area with a dressing
soaked in the gel and lightly bandage. these procedures can be continued
during transit to hospital.
-
Send to the Accident and Emergency
Department.
Eye contact:
Gassing:
-
Remove the casualty from the
contaminated area and place in fresh air.
-
If necessary, resuscitate the casualty.
-
If suitably trained, give oxygen.
-
Send to the Accident & Emergency
Department.
Swallowing:
-
Never attempt to induce vomiting.
-
If the casualty is conscious, rinse out
their mouth with water.
-
Send to Accident & Emergency Department.
Obviously,
hydrogen-related fluorine compounds are extremely
dangerous. While hydrofluorosilicic acid breaks down
in water, the raw material poses a significant
threat to those who come into contact with it.
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