Fluoride deposition :: freshwater ecosystems

Key Concerns:

The main sources of fluoride contamination of water are fluorite deposits (e.g. Pennine mining areas) and run-off from industrial processes. Fluoridation of domestic water supplies increases the fluoride content to 1 mg l-1. It is extremely unlikely that fluoride deposition occurs at a sufficiently high rate to increase the fluoride content of water even to that level, let alone to toxic levels. Therefore no critical load is recommended and the following is provided solely as background information.

Terrestrial plants normally take up little fluoride from the soil, but in the aquatic environment plants probably take up much more. However, there is very little known about the dose-response relationships of aquatic plants.

In some mammals (e.g. humans) water is the main route of exposure to fluoride so the risk in an aquatic environment may depend on the amount of water consumed by the animal. Excess fluoride in the diet of mammals can cause:

• Lesions in developing teeth
• Abnormalities in the bones that can lead to stiffness,lameness and inadequate food intake.

The percentage of the population affected and the severity of the symptoms increase with the concentration of fluoride in the diet and the duration of exposure. Accumulation of fluoride in bone can be reversed if the diet is changed but tooth lesions are irreversible.

Based on data on the bank vole (Clethrionomys glareolus), the animal that is most likely to be at risk in freshwater habitats, in the UK, is the water vole (Arvicola terrestris), especially if it feeds on vegetation that is growing in contaminated water.

Inorganic fluorides are used as insecticides (at very high concentrations) and there are reports of deposited fluoride affecting silk worms in China. However, there is no evidence that invertebrates are affected by the fluoride concentrations that occur in the UK environment. Fluoride is deposited in calcified tissues so crustaceans and molluscs usually have high concentrations. In Antarctic krill the fluoride is known to play an important part in hardening the mouthparts so it might be regarded as essential. There has been a great deal of research on the toxicology of fluoride to invertebrates but mostly using extremely high concentrations (Camargo 2003).

A recent review by the WHO (2002) indicates that the Lowest Observable Effect Level for aquatic invertebrates is over 10-20 mg F l-1, which is only likely to occur in industrial effluents.

Biomagnification of fluoride in food chains does not occur so predators are not at greater risk than herbivores. Scavengers and detritus feeders tend to have higher fluoride concentrations than other groups, but this is mostly because of the contribution of the gut contents to the total body load.

Additional Comments:

There are no reports of fluoride deposition causing environmental problems in water. Search by 'Species' to see further information on fluoride deposition impacts on mammals and macro invertebrates.