Fluoride: A review of its fate, bioavailability, and risks of fluorosis ingrazed-pasture systems in New Zealand

Fluoride(F) is an essential element for animal growth, not readily taken up by plants from soils, yet cases of acute fluorosis in grazing animals caus ed by ingestion of phosphatic fertilisers, volcanic ash, and industrial was tes remind us of its potential hazard. Fluoride concentrations in topsoils slowly increase where annual inputs through atmospheric pollution and phosp hatic fertilisers exceed losses. This paper reviews information on the fate off in grazed pasture systems with the aim of assessing the potential toxi city of accumulating soil F. A preliminary F-cycling model for grazed pastu res, based on the review of international literature and F concentrations i n selected New Zealand pasture soils, indicated that grazing sheep and catt le obtain over 50% of their dietary F land this may be >80% during winter) from soil ingestion. The model suggests that at the extremes of the ranges of the measured winter soil ingestion (143-300 g d(-1) for sheep and 900-16 00 g d(-1) for cattle) and dietary F absorptivity (bioavailability) of soil F (20-38%), total topsoil F concentrations in the range of 372-1461 mu g F g(-1) could cause chronic fluorosis in sheep and 326-1085 mu g F g(-1) in cattle. We recommend that research is undertaken to measure F accumulation rates and soil F dietary absorptivity for a range of intensively managed Ne w Zealand pasture soils.