What is Fluorosis?
Excessive fluoride intake can lead to fluorosis (sometimes called phosphate poisoning) which in severe cases has caused animal deaths.
Fluorine is a natural element, present in soils, plants and animals. It is naturally present in phosphate rock and phosphate fertiliser. Fluorine is assumed to be an essential element in animals. The New Zealand Drinking Water Standards recommend that water supplies have 0.7 to 1.0 mg/litre of fluoride, which is the optimal level in New Zealand to maximise the prevention of dental caries and to minimise the risk of dental fluorosis .
New Zealand soils appear to have fluorine levels consistent with those internationally while our waters have an unusually low concentration (ranging between 0.1 to 0.3 ppm).
Good fertiliser practice recommends that animals should not graze paddocks which have received phosphate fertiliser until at least 25mm of rain has fallen or at least 21 days after being top dressed. During this time animals should be grazed on paddocks not top dressed, or given alternative fodder.
Volcanic ash can also have high levels of fluorine and so volcanic ash deposits on pasture can pose a risk of fluorosis to grazing livestock.