Fluoride generates considerable controversy in human health, largely as a result of the common practice of fluoridating municipal water supplies. We were not, however, able to find any convincing experimental studies that suggested the dramatic effects associated with acute exposure to relatively large doses of F- carried over to low level, long-term exposure. Although there are a few reports of dental fluorosis in people at slightly lower concentrations, the current primary drinking water standard for human consumption is 4 mg F-/L; the secondary standard, apparently based upon cosmetic dental effects, is 2 mg
Our search of the literature pertaining to fluorosis in animals yielded similar results. We were not able to find any reports of toxic effects in livestock or wildlife that occurred at lower F- dosages than cause osteo-dental fluorosis. Thus, as a practical matter, maximum tolerable concentrations of F- in water for livestock and wildlife should be based upon dental and osteal effects.
The effects of F in feedstuffs and water are additive; what really counts is the total dose of biologically available F- ingested by the animal. Most of the reports we reviewed, when reduced to mg F-/kg BW, indicate the threshold dose for chronic osteo-dental fluorosis in cattle is approximately 1 mg F-/kg BW. This is in agreement with the NRC,147 which indicates 30-40 ppm dietary F- (which translates to 0.75-1.0 mg F-/kg BW) is the tolerance level for the more sensitive (i.e. during dental development) classes of cattle.
Numerous studies have demonstrated the susceptibility of wild ungulates (deer, elk, etc.) to fluorosis; however, there has been only one controlled experiment211 from which dose-response can be extrapolated. A few other epidemiologic studies provide sufficient data to form rough estimates of the amount of F- required to produce signs of fluorosis in cervids. Taken together, these indicate wild cervids are approximately as sensitive to the toxic effects of F- as cattle. Sheep seem to be slightly less sensitive than cattle although one Australian report indicated long-term exposure to as little as 10 mg F-/L drinking water in Queensland decreased wool production.202 Given temperatures in that region, water consumption probably resulted in 1-2 mg F-/kg BW for much of the year. The sole report that included any data on horses suggested horses are two-fold more tolerant than cattle, but it goes on to describe situations in which ruminants and horses, sharing a pasture and water supply, were similarly affected.
Assuming Wyoming forages normally contain less than 10 ppm F 213, a water concentration of 3.75 mg F-/L would be required to achieve the 1 mg F/kg BW necessary to cause fluorosis in cattle, and water containing less should not cause measurable production problems.
We recommend water for cattle contain less than 2.0 mg/L F-. By extension, these waters should also be safe for sheep, cervids, and probably horses.