UPTAKE OF FLUORIDE INTO DEVELOPING SHEEP TEETH, FOLLOWING THE 1995 VOLCANIC-ERUPTION OF MT RUAPEHU, NEW-ZEALAND

In the southern Spring of 1995 (mid-October) the active volcano Mt Rua pehu in the central North Island of New Zealand erupted explosively, s preading up to 40 million m(3) of rhyolite tephra over thousands of km (2) of farmland during the lambing season. This ash contained a high c oncentration of soluble fluoride, and more than 2000 lactating ewes di ed of acute fluoride poisoning. To investigate the effects of this bri ef but acute dose on the teeth of grazing animals we examined the dist ributions of fluorine and calcium in the permanent incisor teeth of sh eep which were one year old at the time. Where part of an incisor had been in the first (secretory) stage of calcification the erupted tooth disclosed surface pitting, a thin layer of enriched mineral across th e enamel with as much as 1000 ppm F w/w, and a separate layer with sim ilar to 4000 ppm down the dentine. The part of an incisor which had at tained the later (maturation) stage showed enriched layers only in the outer enamel and in the dentine. This study has demonstrated some imp ortant features of the calcification process, and the risk of fluoride toxicity to grazing animals. (C) 1997 Elsevier Science B.V.