Tag Archives: University of Otago

False balance and straw clutching on fluoridation

The alignment of the poster above with a “balanced” duo of opinion pieces on fluoridation in the recent issue of the Journal of primary healthcare is just too good not to comment on.

The articles are:

Looks a bit uneven, doesn’t it? A Professor of  Dental Epidemiology and Public Health “balanced” against a political  activist? Worse, Atkin’s organisation is an astroturf one set up by the Fluoride Action Network of NZ (FANNZ). Rather clumsily, I add, as they use the same office address! (See Anti-fluoridationist astro-turfing and media manipulation).

Still, I want to comment on the chemical arguments used by Atkin. He is effectively clutching at straws, using very naive interpretations of the chemistry of fluorosilicates and fluoride. As a chemist I find such opportunist distortion of chemistry offensive. Problem is, his and similar arguments are often presented by anti-fluoridation activists and lapped up by their supporters.

Fluorosilicic acid and sodium fluorosilicate are common fluoridating chemicals. When diluted in water the fluorosilicate decomposes to form silica and the fluoride anion. Some anti-fluoridation activists, including Mark Atkin, deny this becuase they wish to deny the relevance of studies showing the safety of fluoride at concentrations used in fluoridating drinking water. So they advance the bogey of  an especially toxic fluorosilicate species. Atkins condenses two of their arguments in this succinct statement:

“Silicofluorides do not fully dissociate to form free fluoride ions in aqueous solution and revert to the silicofluoride ion in acid stomach conditions.”

Hydrolysis of fluorosilicate.

There is some straw clutching going on here in the discussion of the chemistry of fluorosilicates and fluoride which distorts the real chemistry.

The Nuclear Magnetic Resonance work of Finney et al (2006)  (“Reexamination of hexafluorosilicate hydrolysis by 19F NMR and pH measurement”) showed complete decomposition of fluorosilicate species at neutral pH values on dilution. They also showed the presence of surviving fluorosilicate species at low pH values (3 and below) – which is of course irrelevant for water treatment. No one is going to produce drinking water at such acidic values.

Anti-fluoride people are using the observation at low pH values to claim that fluorosilicate species remain in solution at neutral pH values. They sometimes also rely on studies where authors have expressed their results with an indication of precision. For example, Atkin’s activist organisation (the NZ Fluoridation Information Service) claims fluorosilicates:

“do not completely break down into Fluoride ions. This was shown by Crosby in 1969.”

But Crosby (1969) (“Equilibria of fluorosilicate solutions with special reference to the fluoridation of public water supplies”) actually reported:

“sodium fluorosilicate, at the concentration normally present in public water supplies, is dissociated to at least 95%.”

Atkins and his organisation are clutching at a very weak straw there.

Let us be clear – the research indicates that within experimental precision the deocmposition of fluorosilicates is complete and, as expressed by Urbansky (2002), (“Fate of fluorosilicate drinking water additives”):

“equilibrium should have been achieved by the time the water reaches the coinsumer’s tap  if not by the time it leaves the waterworks plant.”

Reversion of fluoride to fluorosilicate?

Atkin’s claim of reversion of fluoride to fluorosilicate “in acid stomach conditions” is also incorrect. He is relying on a simplistic misunderstanding of the nature of “dissociation” of fluorosilicate on dilution.

It is important to recognise the “dissociation” of fluorosilicate species into fluoride and silica at neutral pH values is, in effect, a decomposition. Because of the polymerisation of the silica, and the olation and oxolation reactions involved, the equilibrium is driven to completion – in effect the silica is removed from the reaction. (While it may remain in “solution” or “suspension” for a time it is effectively inert – due to olation – as far as the equilibrium is concerned).

What do I mean by olation? While monomolecular Si(OH)4 is formed on dissociation of the fluorisilicate it rapidly undergoes reactions which lead to exclusion of water and the transformation of Si-OH bonds to Si-O-Si bonds.

(HO)3Si-OH + OH-Si(OH)3

↓ Olation

(HO)3Si-OH-Si(OH)3 + OH

 Oxolation

(HO)3Si-O-Si(OH)3 + H2O

Eventually this leads to formation of colloidal and solid silica. But even while in solution olation and oxolation reduces the reactivity of the silica species.

Just as fluorosilicate species do not reform in your tap water, they do not reform in your stomach. Even if the silica is still in suspension it is no longer present as mono-molecular Si(OH)4 and is effectively inert. So despite the low pH there is no simple equilibrium. Remember too, your drinking water will contain silica derived from other sources besides fluorosilicate (which is probably a minor contributor).

Sure, one can prepares solutions in the laboratory at pH values of 3 or less that contain fluorosilicate species – but once decompostion (involving loss of silica reactivity) occurs at neutral pH values the reaction  is not easily reversed. Especially considering the time lapsed between decomposition of the fluorosilicate and drinking water entering one’s stomach.

HF in stomach

But Atkin still has a fallback postion – if the fluorosilicate doesn’t get you the hydrofluoric acid will. He aserts:

“that 40% of ingested fluoride is absorbed through the stomach wall as molecular hydrofluoric acid (a known mutagen). This negates the ‘all fluoride ions are the same’ deception.”

Yes, in the acid conditions of your stomach F anions will exist in equilibrium with the protonated HF species.

H+ + F ↔ HF

This is also true for other weakly acidic anions – even sulphate – that is just simple chemistry. But, the real danger of the solution in your stomach is that it is very acid, it has a low pH – a very high concentration of hydrogen ions. It is the hydrogen ions that are corrosive. (If anything, the presence of weakly acidic anions like fluoride will actually lower the acidity by removing some of the hydrogen ions). One does not put one’s hand, or any other sensitive tissues, into acidic solution like this. However the stomach is built to handle these conditions.

I understand the molecular species involved in the transfer of fluoride across the stomach wall cells into the blood stream is HF. (Once in the blood HF will convert to fluoride because of the higher pH). So clearly the low pH assists in uptake of F by the body. Don’t forget the concentrations of fluoride, and therefore HF, is actually very low. The protonated species in your stomach solution are not equivalent to the HF (or HCl and H2SO4) chemicals we are used to in their concentrated forms in the laboratory.

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Experts speak out on fluoridation

How Fluoride Works

This is a letter to Dunedin City Councillors from 21 senior School of Dentistry staff. They believe that fluoridation of Dunedin’s water supply should be retained and expanded. As the Otago Daily Times headline puts it – Better oral health largely due to fluoridation.

I think it is a good summary which should be read more widely than in Dunedin. In the upcoming local body elections there will be referenda deciding on local fluoridation in Hastings, Whakatane and Hamilton. There are also campaigns against fluoridation in Auckland and Wellington with declared intentions to spread the campaigns even wider.

Here is the letter:


In 1958, the Faculty of Dentistry requested the council to fluoridate the water supply of our city.

The Otago Branch of the Dental Association pledged its support of this request.

Our position remains unchanged after 55 years.

A debate surrounding community water fluoridation has recently surfaced again in Dunedin, and has received some coverage by local and national media.

We would, therefore, like to remind councillors of the strong case for fluoridation to continue in our city, and be expanded wherever feasible, including to unfluoridated areas of Mosgiel and areas covered by the Northern Water Scheme.

The New Zealand Ministry of Health has commissioned extensive reviews, which have led to development of ministry guidelines and statements on fluoridation.

These guidelines and statements are clear: community water fluoridation is effective and safe, and community water supplies should be fluoridated at 0.7-1.0 parts per million (ppm) wherever feasible.

The Australia New Zealand Food Safety Authority also approves the addition of fluoride to bottled drinking water, as it believes this is important for public health.

The US Centers of Disease Control estimate that for every $1 spent on water fluoridation, $38 is saved on tooth decay treatment, and named water fluoridation as one of the greatest public health improvement measures of the 20th century.

The World Health Organisation considers access to fluoride to be a human right.

Scientific evidence shows that there remains a very strong public health case for continuing and expanding the use of community water fluoridation, because it improves New Zealanders’ oral health and quality of life.

While the extent of tooth decay has reduced in recent decades, the disease remains more prevalent than other significant health conditions in New Zealand (such as asthma), particularly in unfluoridated areas and among disadvantaged New Zealanders.

The recent New Zealand Oral Health Survey found much less tooth decay in fluoridated than in non-fluoridated areas.

The argument that water fluoridation is no longer necessary due to better oral health in New Zealand is not correct.

In fact, the improved oral health we now enjoy in New Zealand compared to the past is in no small way a direct result of water fluoridation.

We forget that very few New Zealanders are affected by water-borne diseases, thanks to water chlorination.

If chlorination was not used, we would have more water-borne diseases.

If community water fluoridation ceased, the severity of tooth decay would increase again, back towards historical levels.

Fluoride is a naturally occurring substance which is present at varying concentrations in water.

It is even detectable at 0.1ppm in the water of the Rattray St ”Speight’s” spring.

Community water fluoridation is not just a matter of fluoride addition; rather, it is the adjustment of fluoride levels up (or even down) to an optimal effective level for the prevention of tooth decay.

Adjusting the background fluoride level (which is generally about 0.3ppm) to 0.7-1.0ppm has a significant effect of reducing tooth decay among people of all ages.

This is particularly important in New Zealand, as we are a country with very little in the way of a publicly funded ”safety net” for adults who cannot afford dental care.

We also now know that, rather than being a disease of childhood only, tooth decay continues through life.

We respectfully request that when councillors consider the fluoridation issue, they be aware of current Ministry of Health guidelines and statements on fluoride, and that when formulating strategy they consult relevant experts at the University of Otago and the Southern District Health Board who are familiar with the relevant peer-reviewed literature.

The opinions of those experts are strongly endorsed by the Otago Branch of the New Zealand Dental Association, the New Zealand Dental Hygienists’ Association and the New Zealand Dental and Oral Health Therapists’ Association.

The Otago Branch unequivocally supports the national Dental Association’s 2012 statement on water fluoridation.

We also advise councillors that anti-fluoridation arguments are often based on un-refereed internet resources or books that present a highly misleading picture of water fluoridation, rather than being based on objective science.

With this letter, we have included copies of an excellent Australian article from the journal Australia and New Zealand Health Policy, and the Victorian government publication Water fluoridation helps protect teeth through life.

Both are short, and are written for the benefit of public health officials.

We trust that the council will make the sensible public health decision to retain and expand community water fluoridation in our city.

See also

Other articles on fluoridation
Making sense of fluoride Facebook page.

Answer simple question – win an iPad

The catch – you are limited to 140 characters on Twitter.

Oh, yes, also the entry must “explain the origins of the Universe.”

Credit: Wikipedia

Simple – should be plenty of entries for that!

I guess the trick is in the syntax, as well as the science.

Have a look at Otago University‘s Centre for Science Communication Twitter Competition for the details.

Deadline is Tuesday 15 November. You will have a chance to vote on your favourite entry from Wednesday 16 November until noon Saturday 19 November.

And, Professor Lawrence Krauss, author of the forthcoming book A Universe from Nothing: Why There Is Something Rather than Nothing, will then select the winning tweet from the five tweets receiving the highest number of votes.

I still have a week or so to solve that problem and send my entry.

Thanks to: Best Science Tweet Competition.

New science blogs in New Zealand

This last week has seen the entry of three new science bloggers onto the New Zealand scene. Or more specifically the SciBlogs NZ scene.

Southern Genes is the blog of Genetics Otago. It has members, and hence contributors, from University of Otago, but also in AgResearch and Abacus Bio. There are also members from the University of Otago Christchurch and Wellington campuses. Genetics Otago members have interests in all aspects of genetics; from science to the impact of genetics on society and law.

So we expect many and varied posts at Southern Genes. But all interesting.

Jesse Dykstra is writing for Shaken Not Stirred. He is a PhD student in the Natural Hazards Research Centre at Canterbury University and has studied natural hazards in Fiordland, Alaska and British Columbia. Looks like he will have plenty to write about –  and not too far from home. He is currently running a series on the Canterbury earthquakes.

From seeing data blog

And then there is Chris McDowell. He works as an informatics researcher at Landcare Research helping look after some of New Zealand’s environmental datasets of national significance. Chris develops tools to help scientists visualise data. Have a look at his blog seeing data and his recent post on Mapping quakes in Canterbury.

Have a look at these new blogs. They are sure to be interesting.

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NZ’s largest science blog network goes live

sciblogs adYou will notice a rash of new science blogs based in New Zealand. Maybe you have already.

This press release explains it all.

The Science Media Centre today launches a major new science communication effort with the arrival of Sciblogs, a network of science blogs covering everything from clinical health to climate change.

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