Erupting volcanoes are an impressive but deadly force.

Apart from blasting out tonnes of ash, rock and lava, volcanoes release clouds of poisonous gases into the atmosphere. One of the most dangerous is hydrogen fluoride.

It promotes acid rain and attaches to ash particles, polluting grass and streams.

Some volcanic eruptions, particularly in Iceland, have released enough fluorine compounds to cause fluorosis, a crippling bone disease, in the local livestock. In other volcanic areas, people exhibit mottling of the teeth (dental fluorosis).

Fluorine is the most reactive element of the halogen group of chemicals and bonds easily with other elements, becoming a fluoride.

Calcium fluoride occurs naturally in UK drinking water and is relatively harmless.

However, the fluoride used to artificially fluoridate water is not calcium fluoride but a toxic waste from the phosphate fertiliser industry called hexafluorosilicic acid.

Most dentists will tell you that fluoride helps to prevent tooth decay. As well as increasing resistance to corrosive acid, they say, it inhibits bacterial enzymes.

Dentists maintain that as sugar consumption in this country is very high, there would be rampant tooth decay in children were fluoride not added to toothpastes, drops, gels and mouthwashes.

But are we having too much of a good thing? Antifluoride campaigners argue excess fluoride causes staining of the teeth and is highly toxic. They say dental fluorosis is the visible manifestation of chronic fluoride poisoning which weakens bones, causes hip fractures and thyroid disorders.

Once added to the water supply, it also enters the food chain and it becomes impossible to control the amount of fluoride an individual is exposed to.

Children's toothpastes offer a variety of enticing flavours which only encourages them to swallow it. In the US, therefore, there is a mandatory warning on every tube of fluoridated toothpaste:

"In case of accidental ingestion, seek professional assistance or contact a poison centre immediately."

Fluoride has another sinister habit: It combines well with aluminium. Toxic in excessive amounts, the symptoms are similar to those of Alzheimer's and osteoporosis.

Elemental aluminium cannot be transported into the brain but aluminium fluoride easily penetrates the bloodbrain barrier.

Many water supplies are treated with aluminium sulphate to make the water appear clear.

The majority of European countries have stopped or banned water fluoridation but in the UK ten per cent of the drinking water is still fluoridated (not in Sussex).

Apart from dental products, other sources of fluoride are tea, pesticides and some drugs, including tranquillisers. Steel and aluminium plants emit high levels into the air and phosphate fertilisers increase fluorides in the soil.

Dentists are right to be concerned about the state of children's teeth. However, fluoride does not address the cause of tooth decay. As we are already exposed to unknown quantities of fluoride, the solution lies in changing our eating habits.

For more information,
contact the National Pure Water Association (Campaign for Safe Drinking Water), 12 Dennington Lane, Crigglestone, Wakefield WF4 3ET. Telephone 01924 254433 or visit the web site at www.npwa.freeserve.co.uk