A new science-based report on the mass fluoridation of South African drinking water has raised several red flags – including extra health risks for tens of thousands of HIV/Aids sufferers, kidney patients, the elderly and other “sensitive” groups.

Many of the potential costs – to people, the environment and the economy – have not been properly assessed by the government and need more detailed research, according to a report compiled by the Water Research Commission (WRC).

It identifies “major” gaps in the ability to predict public health risks and says the toxic effects of fluoride could also be more severe for HIV/Aids patients with weakened immune systems, especially if they are also poorly nourished.

Malnutrition is a particular risk for Aids patients, many of whom suffer from chronic diarrhoea.

If fluoridation goes ahead, the report says, it might be necessary to advise Aids sufferers to drink bottled water to reduce their fluoride intake. Mine workers in Gauteng may also be exposed to three times as much fluoride as the rest of the population because they drink abnormally high volumes of water while working in hot and humid underground environments.

The new WRC report examines several aspects of the government’s compulsory and controversial plan to add small concentrations of fluoride to drinking water across the country as a way to reduce tooth decay among the poor.

It cites a recent national survey of oral health which suggested that nearly 60% of 6-year-old children suffered from some degree of tooth decay, although overall levels of dental problems in South African children were regarded as “low” when measured against World Health Organisation standards.

The compulsory fluoride policy was due to begin in South Africa’s largest cities in September 2003, but implementation is on hold because of the latest publication, and after concerns raised with a parliamentary committee on water issues earlier this year.

The WRC report, Feasibility of water fluoridation for South Africa, has chapters by several local scientists or consultants, and recommends that fluoridation should not be rushed until uncertainties are cleared up.

“In a country as diverse as South Africa, it is obvious that one size cannot fit all.”

The authors conclude that although mass fluoridation could help to reduce dental decay among the urban poor, the yearly addition of nearly 4 200 tons of fluoride to South African water is “not a trivial or risk-free undertaking”.

“The responsible implementation (of fluoridation) in South Africa, with its unique problems and conditions, will require hard work and the elucidation of a number of areas of uncertainty.”

According to Bettina Genthe, from the CSIR’s Environmentek division, several studies showed that fluoride was extremely toxic at high doses, yet there was considerable scientific uncertainty about the exact “threshold level” where flouride would not harm human health in some way in the long term.

Many of these risks could not be measured directly, but could only be estimated using incomplete scientific data.

Although there was evidence that fluoride caused cancer in young male rats, studies on human cancer were inconclusive.

The so-called York Review of 2000, a survey commissioned by the chief medical officer of the United Kingdom, reached the conclusion that there was no evidence that water fluoridation caused cancers of any kind.

This should not be interpreted as proof of fluoride safety, but rather as inadequate research of high quality.

More recent research also points to a link with bone cancer in men, while “vast numbers” of studies support findings that fluoride is able to cause mutagenicity (genetic changes), a further indication of cancer-causing potential.

A number of medical studies also demonstrate the ability of fluoride to affect human immune systems at low concentrations (at just above the 0.7mg/litre guideline for South Africa). This is particularly significant, the authors say, because there is very little information on the overall exposure of South Africans to additional sources of fluoride via food, dust, air or toothpaste.

The uncertainty over total fluoride exposure (excluding drinking water) is “extremely large”.

“Internationally, we have limited or no data on total exposure to fluoride in all media and via all pathways. This is a major shortcoming in being able to accurately predict adverse health effects and, therefore, in our ability to protect public health.”

Genthe singled out several groups of people thought to be at increased health risk from fluoridation – the malnourished, HIV/Aids sufferers, the elderly, those with heart and blood circulation problems and kidney patients.

“South Africa has a very large potentially sensitive population that may experience the detrimental effects of fluoride at the proposed water fluoridation concentration. There are many unknown factors with regard to the toxicity and carcinogenicity (cancer potential) of fluoride and this may be exaggerated in the immuno-compromised.”

The chapter on environmental fluoride levels, by consultants Dr Chris Herold and M J van Veelen, also raises red flags about the total new load of fluoride which would enter South African rivers. Because of evaporation and the loading of river and dam water with extra fluoride, drinking water in several downstream areas may reach levels higher than the national guideline.

They note that their assessment is based on data collected during a period of unusually wet climate conditions – so the conclusions might have been distorted to show an under-estimation of predicted fluoride levels.

Responsible

“A less biased analysis based on a longer hydrological sequence is required to give a more balanced view of the likely impact.”

They ask who will be responsible for the massive costs of removing fluoride from drinking water in places where the national guideline is exceeded.

The chapter on technical and engineering issues by Prof Johannes Haarhof, of Rand Afrikaans University, highlights the importance of strict water monitoring and staff training to reduce the risk of overdosing drinking water with a compound as toxic as fluoride.

“Only one example of an overdosing event will be quoted to illustrate its damaging consequences. In 1993 there was an equipment failure in the town of Middleton, Maryland, which caused overdosing of water. As a result, the entire supply system had to be drained, its customers supplied with bottled water, and fluoridation permanently discontinued.”

In the chapter on social and legal issues, author Gillian Sykes notes that – unlike Americans – South Africans will have no choice in deciding whether fluoridation should go ahead.

Some countries, including the United States and Canada, made allowance for a popular vote before implementing fluoridation.

Because there was no allowance in South Africa to “opt out” by choice, it was possible that opponents of mass water fluoridation could mount a constitutional court challenge.

“(One of) the arguments against public water fluoridation from a constitutional viewpoint is that dental caries are neither communicable nor contagious, and that those most at risk can receive treatment through less invasive and more discreetly targeted means.”

Sykes also raises questions about the government’s plan to implement fluoridation selectively in five or seven so-called “front-runner” cities and municipalities.

Though she does not mention the emotive term “guinea pig”, Sykes says the government should take care to explain the purpose of the front-runner process.

“Is it to generate lessons for wider implementation of fluoridation in the near future, or are they longer-term pilots to determine the health effects of water fluoridation?”