7. Does the fluoridation of drinking water specifically lead to adverse ecological impacts?
The committee considered environmental exposures from use of fluoridated water as drinking water, And other domestic uses. This will pass into the environment via drainage and sewage treatment. Most fluoride remains in solution, so the solid component of sewage sludge passes little fluoride onto land, or into the atmosphere when it is incinerated. The properties of the fluoride ion also mean that little of the fluoride which passes into waterways and lakes enters sediment. This means its effects are largely confined to water-dwelling organisms in aquatic ecosystems.
As the question posed relates specifically to artificial fluoridation, it is assumed this will not entail raising any water levels above those defined as legal limits for fluoridation – 1.5 mg/L in the EU and 0.8 mg/L in Ireland.
Reviews of studies on effects of fluoride on aquatic organisms suggest that the most sensitive organisms, marine invertebrates, may feel some adverse effect at 2.9 mg/L fluoride or above. This leads to setting a Predicted No Effect Concentration (PNEC), with a factor of ten as a safety margin, pf 0.29 mg/L.
The question the is whether a typical artificial fluoridation level, taken as 1.0 mg/L, will be diluted enough in water treatment to fall below this threshold. This is extremely plausible in most circumstances.
On the basis of this, and other calculations and modelling, the SCHER is of the opinion that adding fluoride to drinking water does not result in unacceptable risk to water-dwelling life.