TOXICOLOGY: Fluoride / Fluorine (F) -- An Overview

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(A) FLUORIDE

10.1 INTRODUCTION
• …high levels of waterborne F are also hazardous to both human and animal health. For example, in
China and India millions of people are suffering from dental and skeletal fluorosis – abnormal or
poisoned tooth and bone conditions induced by F – mainly due to consumption of high levels of F in
drinking water.

10.2.5 FOODS
• F intake from food and beverages by a male residing in a fluoridated community in the U.S. is about 1
to 3 mg/day. It is decreased to 1.0 mg/day in a nonfluoridated area. The intake from drinking water
ranges from 0.1 to 0.5 mg/day in nonfluoridated communities, whereas in fluoridated communities it
may amount to 1 to 2 mg/day.
• Several plant species are known as F accumulators. Examples include camellia (620 ppm), tea (leaves,
760 ppm), and elderberry (3600 ppm, dry basis).

10.3 INDUSTRIAL SOURCES OF FLUORIDE POLLUTION
10.3.2 MANUFACTURE OF PHOSPHATE FERTILIZERS
• In the aqueous scrubber, SiF4 readily reacts with water, forming fluorosilicic acid (H2SiF6), as shown in
Reaction 10.3. Fluorosilicic acid is highly soluble in water and is readily absorbed by plants.

10.3.3 MANUFACTURE OF ALUMINUM
• A number of other substances are emitted in the process. This is because several catalysts, including
CaF2, AlF3, and cryolite, are used in the eletrolysis of alumina, and as these are heated at high
temperatures, some will escape from the cells, contaminating the surrounding atmosphere.
• …several other gases, including SO2, SiF4, HF, COS, CS2, He, and water vapor, are also produced…
• Moreover, a large number of particulates are also emitted, including Al2O3, carbon (C), cryolite, AlF3,
CaF2, Fe2 O3, and chiolite (Na5Al3F14).

10.3.4 MANUFACTURE OF STEEL
• In the manufacture of steel, calcium fluoride (CaF2) is used as a flux… F compounds emitted from this
operation include HF and CaF2.

10.3.5 COMBUSTION OF COAL
• As mentioned previously, coals mined in U.S. contain about 0.001 to 0.048% F, usually as fluorapatite
or fluorspar. Combustion of coal in power plants, therefore, emits considerable quantities of F into the
atmosphere. During combustion, about half of the F in coal is emitted as gaseous HF and SiF4 and
particulate matter.
• For example, studies show that several cities in China, including Chongqing and Beijing, are
experiencing severe fluoride air pollution problems arising mostly from coal combustion.
• Another important source of F in Beijing is dust from fresh concrete used for construction.
• Fluoride has also been traced to runoff from application of insecticides and herbicides.

10.4 EFFECTS ON PLANTS
• HF is the most phytotoxic air pollutant.
• F accumulates in the foliage of plants. The plants then serve as a vehicle for transfer of F to herbivores,
with the potential for inducing dental and skeletal fluorosis.

10.5 EFFECTS ON ANIMALS
10.5.1 INTRODUCTION
• Animals normally ingest small amounts of F in their rations without observable adverse effects, but
excessive intake can be detrimental.

10.5.3 CHRONIC EFFECTS
• The two most conspicuous and thoroughly studied manifestations of chronic F poisoning are dental
and skeletal fluorosis. Once absorbed into animal body, F has a great affinity for developing and mineralizing teeth. This affinity can either enhance tooth development or induce dental lesions,
depending on the amounts of fluorides ingested.
• Furthermore, it is often found that F levels are inversely related to the distance between the industrial
facilities and the site of animal collection.
• Lameness or stiffness is an intermittent sign of F toxicity. … The clinical basis for the lameness is not
well understood.

10.6 EFFECTS ON HUMANS
10.6.1 DAILY INTAKE
• Daily intake of F by individuals in the U.S. is about 0.2 to 0.3 mg from food, 0.1 to 0.5 mg from water (1
to 2 mg if water is fluoridated), and varying quantities from beverages (F content of wine is 0 to 6.3
ppm, beer contains 0.15 to 0.86 ppm, and milk, 0.04 to 0.55 ppm). The amount of F inhaled from air is
about 0.05 mg/day.
o NOTE: Toothpaste not mentioned (1 or 2 times daily), dermal contact and inhalation during
showering / bathing / swimming is also not mentioned.
o There is approximately 1,000 ppm F in toothpaste and approximately 0.22 ppm F is actually
ingested by a 5 year old child per brushing. This does not include what remains in the mouth
when done / rinsed.

[link to www.fluoridealert.org]
o Soda usually contains approximately 0.60 ppm F, infant formula, processed cereals, juice,
cigarettes, and fluoridated salt are other sources.

[link to www.fluoridealert.org]

10.6.2 ABSORPTION
• Absorption of F from the gastrointestinal tract occurs through a passive process; it does not involve
active transport.1 Absorption is rapid and probably occurs in the lumen. The rate of absorption is
dependent on the F compounds involved, e.g., 97% of NaF, 87% of Ca10F2(PO4)6, 77% Na3AlF6, and
62% CaF2 are absorbed. About 50% of the absorbed F is excreted by the kidneys while the remainder
is stored, primarily in calcified tissues.
• Even at low levels of F intake, appreciable levels of F will, in time, accumulate in calcified tissues.

10.6.3 ACUTE EFFECTS
• The lethal dose of inorganic F has been estimated to be in the range of 2.5 to 5 g for a 70 kg male…

10.6.4 CHRONIC EFFECTS
• Fluoride accumulates in the skeleton during prolonged, high-level exposures. Radiological evidence
shows hypermineralization (osteofluorosis) occurs when bone F concentrations reach about 5000 ppm.
• Fluoride exposure leads to cell damage and induces necrosis. Eventually, F produces massive
impairment in the functions of vital organs, particularly when given orally.
• Airborne F from the combustion of coal was found to pollute extensively both the living environment and
the food, such as corn, chilies, and potatoes, that the residents consume.
• Several groups of researchers have reported reproductive effects of F in humans.
• Levels of reproductive hormones were also measured; the High Fluoride Exposure Group showed
higher follicle stimulating hormone but lower inhibibin-B, prolactin, and free testosterone serum
concentrations than the Low Fluoride Exposure Group.

10.7 BIOCHEMICAL EFFECT
10.7.2 IN ANIMALS AND HUMANS
• F inhibits the metabolism of carbohydrates, lipids, and proteins. In animals and humans, a large number
of enzymes are depressed by F, including enolase, ATPase, lipase, and cholinesterase. Inhibition of
glycolysis, due in part to decreased enolase activity, may be responsible for the hyperglycemia
observed in laboratory animals exposed to F.
• F stimulates adenylcyclase activity in all tissues so far examined…
o From Wikipedia: In neurons, calcium-sensitive adenylate cyclases are located next to calcium
ion channels for faster reaction to Ca2+ influx; they are suspected of playing an important role
in learning processes. This is supported by the fact that adenylate cyclases are coincidence
detectors, meaning that they are activated only by several different signals occurring together.

[link to en.wikipedia.org]
• F also affects functions controlled by Ca in humans, as it does in plants. These functions include blood
clotting, membrane permeability, and cholinesterase activity.
• In the presence of F, Mg2þ and MgADP form a complex MgADP– MgFx that traps the active site of S1
and inhibits myosin ATPase. As previously mentioned, F is shown to inhibit protective enzymes, such
as SOD, glutathione peroxidase (GSHPx), and catalase, in various human tissues. Inhibition of one or
more of these enzymes may allow free-radical-induced reactions to occur, leading to cellular and tissue
damages.

10.8 NUTRITIONAL FACTORS AFFECTING FLUORIDE TOXICITY
• … several nutrients have been shown to alleviate injuries caused by exposure to F. The nutrients
studied so far include proteins and Ca, and vitamins C (ascorbic acid), D, and E. Glutathione (GSH),
which is not a nutrient but a well-known antioxidant, has also been studied.
• …F-treated chicks showed a marked decrease in ascorbic acid levels in the heart, spleen, brain,
gizzard, and pancreas, while the levels were increased in the lungs and kidneys.
• Results showed marked decline of ascorbic acid in adrenal glands and kidneys in the F-treated
cockerels. Furthermore, the levels of DHA in the kidneys of the F-exposed cockerels increased more
than 100% compared with the control levels.
• In laboratory mice, both protein and vitamin C were shown to lower F accumulation in bone. For
example, mice fed a low-protein diet (containing 4% protein) supplemented with 150 ppm NaF
deposited five times more F in the tibia than did control mice fed a regular diet (containing 27% protein)
and exposed to the same level of NaF. Furthermore, supplemental vitamin C greatly lowered F
deposition in the bone.34 (It should be noted that mice also produce vitamin C.)
• Fluoride treatment has been shown to induce embryotoxicity in pregnant rats. … A higher incidence
of skeletal and visceral abnormalities (subcutaneous hemorrhage) was observed in the fetuses of the Ftreated
pregnant rats. Oral administration of vitamin C (50 mg/kg body weight) with NaF significantly
reduced the severity and incidence of F-induced embryotoxicity in the rats.
• Exposure of male mice to NaF (10 mg/kg body weight) for 30 days showed a marked decrease in
cauda epididymal sperm count, motility, and viability, resulting in significant reduction in fertility
rate. Withdrawal of NaF treatment for 30 days produced incomplete recovery. However, when
vitamin E or vitamin D was supplemented during the withdrawal period, the toxic effect of NaF was
significantly alleviated, as the treated mice restored their reproductive functions and fertility.
Additionally, it was found that a combined administration of vitamins D and E was generally more
effective than either vitamin D or E administered alone.

ENVIRONMENTAL TOXICOLOGY - Second Edition
Biological and Health Effects of Pollutants
Ming-Ho Yu
ISBN: 1-56670-670-X

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(B) Scientific Studies
J Toxicol Environ Health. 1994 May;42(1):109-21.

Exposure to high fluoride concentrations in drinking water is associated with decreased birth rates.

Division of Biometry and Risk Assessment, National Center for Toxicological Research, Jefferson,
Arkansas 72079.
A review of fluoride toxicity showed decreased fertility in most animal species studied. The current
study was to see whether fluoride would also affect human birth rates. A U.S. database of drinking
water systems was used to identify index counties with water systems reporting fluoride levels of at
least 3 ppm. These and adjacent counties were grouped in 30 regions spread over 9 states. For each
county, two conceptionally different exposure measures were defined, and the annual total fertility rate
(TFR) for women in the age range 10-49 yr was calculated for the period 1970-1988. For each region
separately, the annual TFR was regressed on the fluoride measure and sociodemographic covariables.
Most regions showed an association of decreasing TFR with increasing fluoride levels. Meta-analysis of
the region-specific results confirmed that the combined result was a negative TFR/fluoride association
with a consensus combined p value of .0002-.0004, depending on the analytical scenario. There is no
evidence that this outcome resulted from selection bias, inaccurate data, or improper analytical
methods. However, the study is one that used population means rather than data on individual women.
Whether or not the fluoride effect on the fertility rate found at the county level also applies to individual
women remains to be investigated.
PMID: 8169995 [PubMed - indexed for MEDLINE]

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Fluoride 1994; 27(1): 7-12

Effect of Fluoride on Rat Testicular Steroidogenesis - Narayana MV, Chinoy NJ

ABSTRACT: In view of reports of infertility among human populations in fluorosis prevailing regions, we
investigated the effect of fluoride ingestion on testicular steroidogenesis in rats. Sodium fluoride (NaF)
was administered to the rats orally at a daily dose of 10mg/kg bodyweight for 50 days. The treatment
did not cause significant change in testicular cholesterol levels, indicating that metabolism was not
altered and that there was no hypo/hypercholesterolemic effect. In addition, activities of the
intermediary enzymes in androgenesis, viz., 3ß- and 17ß-hydroxysteroid dehydrogenase were only
modestly decreased by NaF ingestion. Subsequently, the determination of circulating androgen levels
was similar in NaF-treated rats showed a downward trend compared to those of the control group,
suggesting alteration in testosterone concentration. The histomorphometric studies revealed significant
change in the Leydig cell diameter m correlation with the androgen levels. These results indicate that
fluoride does interfere with steroidogenesis in short-term lowdose exposures in rats.

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(C) Fluoride

Uses
• It is used in hydrofluoric acid, fluoropolymers, and refrigerating agents.

Exposure Routes and Pathways
• Ingestion, dermal exposure (most notably via hydrofluoric acid), and inhalation are possible routes of
exposure.

Toxicokinetics
• Chronic ingestion of fluorides causes exaggerated buildup on teeth, bones, and ligaments. Exposure to
skin, eyes, and mucous membranes has a corrosive effect.

Mechanism of Toxicity
• Fluoride interferes with the metabolism of cells and enzymes. It is a cross-linking agent and rarely
occurs in an elemental state in nature. It is a metabolic inhibitor, interfering with calcium metabolism
and electron transport. Calcium is essential for maintaining cardiac membrane potentials and in
regulating coagulation.

Acute and Short-Term Toxicity (or Exposure): Human
• Chronic over-absorption can cause hardening of bones, calcification of ligaments, and buildup on teeth.
Fluoride can cause irritation or corrosion to eyes, skin, and nasal membranes. Large ingestion of
fluoride salts or hydrofluoric acid may result in fatal arrhythmias due to profound hypocalcemia. ... The
American Conference of Governmental Industrial Hygienists threshold-limit value/time-weighted
average for fluorine is 1 ppm. National Institute of Occupational Safety and Health reports that
concentrations of 25 ppm are immediately dangerous to life and health.

Chronic Toxicity (or Exposure): Animal
• Sheep fed fluoride 10ppm in water over 7 years demonstrated decreased wool production. Flourosis,
painful stiff gait, lameness, decreased milk production, and dental changes developed in cattle fed 40
ppm fluoride in their diet over 6 months to 1 year.

Chronic Toxicity (or Exposure): Human
• Fluorosis is a chronic public health problem in many parts of the world. Exposures to fluoride in
concentrations greater that [sic] 1 ppm result in bone deformities, spinal compressions, and restricted
movements of joints.

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Fluorine

Uses
• The presence of fluorine as a soluble fluoride in drinking water to the extent of 2 ppm may cause
mottled enamel in teeth, when used by children acquiring permanent teeth; in smaller amounts;
however, fluorides are added to water supplies to prevent dental cavities.
• ...Fluorine has been studied as a rocket propellant...
• …involved in ozone depletion and global warming effects... Fluorine will react with water or steam to
produce heat, and toxic and corrosive fumes.

Background Information
• It is the most electronegative and reactive of all the elements.
• Many later investigators, including Davy, Gay-Lussac, Lavoisier, and Thenard, experimented with
hydrofluoric acid, with some experiments ending in tragedy.

Exposure Routes and Pathways
• The general population is exposed to fluoride through consumption of drinking water, foods, and
dentifrices, primarily in the form of sodium fluoride and stannous fluoride.

Toxicokinetics
• Fluoride, rather than fluorine, appears to be the agent that is toxicologically active in the body because
fluorine is so reactive that it is not absorbed chemically unchanged. Existing data indicate that all
common forms of inorganic fluoride are rapidly and quite extensively absorbed. The highest degree of
absorption has been noted with aqueous solutions of sodium fluoride resulting in absorption within 30
min of oral exposure.
• Cessation of exposure will decrease the fluoride levels in bone slowly; however, the rate of decay is
undetermined in humans.

Mechanism of Toxicity
• Fluoride appears to interfere with cell metabolism, and fluoride is a cross-linking agent.
• The inorganic fluoride ion forms metal–fluoride–phosphate complexes that interfere with any enzymes
that require a metal ion cofactor.
• ...the fluoride ion is thought to be a general inhibitor of the energy production organization of the cell,
specifically the oxidative phosphorylation necessary in ATP formation.

Acute and Short-Term Toxicity (or Exposure): Human
• Elemental fluorine and the fluoride ion are highly toxic. Low overdose ingestion produces local
gastrointestinal upset, salivation, and a metallic taste that may last 48 h. Acute inhalation of fluorine can
cause severe respiratory irritation, dyspnea, and death. High overdose ingestion, in addition to causing
more severe local manifestations, may produce systemic symptoms of convulsions, coma,
dysrhythmias, hypotension without compensatory tachycardia, acidosis, paresthesias, and coagulation
disturbances. Hypocalcemia can develop very rapidly. Coagulopathies can develop as a result of
hypocalcemia.
• The acute toxic dose of fluoride ranges from 0.1 to 0.8 mg/kg of body weight.

Chronic Toxicity (or Exposure): Animal
• High doses of fluorine gas and hydrogen fluoride in animal studies have resulted in testicular
degeneration. The available animal and human data strongly suggest that the reproductive system
is a target of fluoride toxicity at high exposure levels.
• The (US) National Institute of Environmental Health Sciences, National Toxicology Program (NTP) oral
carcinogenicity study on sodium fluoride concluded that there was ‘‘equivocal evidence that fluoride is a
carcinogen in male rats, but not in female rats or mice of either gender.’’

Chronic Toxicity (or Exposure): Human
• Chronic exposure to excessive amounts of fluorine can result in mottled teeth (fluorosis), for example, a
chronic fluoride ingestion of 1 ppm of fluoride in drinking water can cause mottling of the teeth, and an
exposure of 1.7 ppm will produce mottling in 30–50% of patients. Chronic poisoning may cause
osteosclerosis, calcification of ligaments and tendons, bony exostoses, and renal calculi. Chronic
inhalation exposure to high levels of hydrogen fluoride and fluoride dusts, or chronic oral exposure to
high levels of fluoride can cause skeletal malformations and severe joint pain, and an increased
incidence of nonvertebral skeletal fractures. The existing data do not indicate that fluoride is a
carcinogen in humans.
• There have been reports of a decrease in fertility in women and decreased serum testosterone
levels in men living in communities with high fluoride levels in municipal water.

In Vitro Toxicity Data
• A fluoride level of 0.4–1.0 mg/l inhibited DNA repair after irradiation of mouse spleen cells in vitro.
Sodium fluoride was not mutagenic in cell cultures of human leukocytes at concentrations of 18 and 54
mg/l.

Environmental Fate
• Fluorine is not destroyed in the environment, but rather it combines with minerals to form salts, which
remain in the soil.
• Calcium carbonate precipitation dominates the removal of dissolved fluoride from seawater. The next
most important removal mechanism is incorporation into calcium phosphates. Undissolved fluoride is generally removed by sedimentation. The residence time of fluoride in ocean sediments has been
computed at 2–3 million years.
• Foods characteristically high in fluoride content are certain types of seafood (1.9–28.5 mg kg/1),
especially those types in which the bones are consumed, bone products such as bone meal and
gelatin, tea, and baby formula processed with fluoridated water.

Exposure Standards and Guidelines
• The American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value, 8 h
time-weighted average, for fluorine is 1 ppm, and the short-term exposure limit, 15 min, is 2 ppm. The
(US) Occupational Safety and Health Administration permissible exposure limit, 8 h TWA, is 0.1 ppm
(0.2mg/m3). The (US) National Institute for Occupational Safety and Health (NIOSH) recommended
exposure level, averaged over a 10 h work day is 0.1 ppm (0.2mg/m3), and the NIOSH Immediately
Dangerous to Life or Health value is 25 ppm.

ENCYCLOPEDIA OF TOXICOLOGY, FOUR-VOLUME SET – Volume 2

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Last Edited by verumlux on 10/28/2009 10:40 PM