Page 462 - Veterinary Toxicology, Basic and Clinical Principles, 3rd Edition

VetBooks.ir Chapter 27

Fluoride

Larry J. Thompson

INTRODUCTION industrial pollutants or volcanic emissions, or through
water containing excess fluorides from industrial pollu-
Fluorine is a member of the halogen group on the periodic
tion or dissolved from natural sources (Shupe and Olson,
table and is rarely found in elemental form in nature but
1971, 1983). Rock phosphates destined for animal diets
instead exists as fluoride, the monovalent anion, com-
must be defluorinated before use or have a phosphorus
bined with other elements. The most common mineral
to fluorine ratio (P:F) of more than 100:1 in order to
containing fluoride is fluorspar, also known as fluorite
avoid exposing the animal to excess fluoride (Osweiler,
(CaF 2 ), and soils generally contain calcium fluoride 2004). Following a long history of problems, industrial
(CaF 2 ). Although now rare, sodium fluoride and sodium
contamination of forages and water with excess fluoride
fluorosilicate (Na 2 SiF 6 ) have been used as insecticides
has decreased due to recognition of the problems caused
and anthelminthics. Sodium fluoroacetate (compound
by excess fluoride and increased regulatory controls on
1080) is another formerly used rodenticide that is rarely
fluoride-emitting industries. Historical point sources for
seen in the United States today but may be found in
fluoride emissions have included the smelting industries
other parts of the world (e.g., Australia). Fluoroacetate
(e.g., aluminum, copper, and steel), brick or ceramic
can also be found naturally in several species of plants
product factories, coal-fired power plants, and the
(Gastrolobium spp., Oxylobium spp. and others). Sodium
phosphate-processing industries. Plant uptake of fluoride
fluoride, sodium fluorosilicate, and fluorosilicic acid have
by translocation from the soil is usually not an important
been used in the United States for the fluoridation of
source of fluoride for grazing animals. Much more sig-
drinking water for humans to prevent the development of
nificant sources include airborne fluoride that settles on
dental caries (CDC, 2001). When the gas hydrogen fluo-
plant surfaces and fluoride from soil that is ingested
ride is dissolved in water it forms hydrofluoric acid, a
directly or contaminates the plant (NRC, 2005). Acute
very hazardous chemical that has industrial and laboratory
fluoride poisoning in large animals is rare but can occur
uses such as purifying metals, etching glass and cleaning
following exposure to fluoride-containing commercial
semiconductors due to its ability to dissolve silicates and
products (Bischoff et al., 1999)ortoash andtephrafol-
metal oxides. This chapter will stress the chronic effects
lowing volcanic eruptions (Shanks, 1997).
of fluoride excess, also called fluorosis or fluoride toxico-
sis, in large animals.
PHARMACOKINETICS AND MECHANISM
BACKGROUND OF ACTION
Fluoride is present at low levels in virtually all feed and Sodium fluoride is readily absorbed from the digestive
water sources, thus animals will have continuing expo- tract and is several times more biologically available than
sure throughout their lifetime. While a small amount of fluoride compounds from feed or environmental sources.
fluoride in the diet has been shown to improve bone and Fluoride is distributed to all parts of the body, with
teeth development, a chronic excess of fluoride can have approximately 50% of absorbed fluoride being excreted
adverse effects on teeth, bone, and other body systems. by the kidneys. The remainder will be incorporated into
Large animals have been exposed to excess fluorides bone and teeth with very little accumulation in the soft
through the ingestion of high-fluoride rock phosphates tissue. Fluoride concentrations in the blood, urine, and
used as nutritional supplements, by the ingestion of soft tissues may reflect recent ingestions but will also
forages contaminated with excess fluorides from increase slowly over time with continuing excess fluoride
Veterinary Toxicology. DOI: http://dx.doi.org/10.1016/B978-0-12-811410-0.00027-1
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