116
Trace Elements in Abiotic and Biotic Environments
Acute high-level exposure to F causes immediate effects of abdominal pain, excessive
saliva, nausea, and vomiting. Seizures and muscle spasms may also occur. Moderatelevel chronic exposure (above 1.5 mg/L of water—the WHO guideline value for F in
water) is more common. People affected by fluorosis are often exposed to multiple
sources of F, such as in food, water, air (due to gaseous industrial waste), and excessive
use of toothpaste. However, drinking water is the most significant source of F. Skeletal
fluorosis and an increased risk of bone fractures occur at a total intake of 14 mg F/day,
and an increased risk of bone effects is at total intakes about >6 mg F/day. In some
regions, the indoor burning of F-rich coal also serves as an important source of F.
Fluorine in water is mostly of geological origin. Water with high levels of F is
mostly found at the foot of high mountains. Intake of F with water and foodstuffs
is the primary causative factor for the endemic skeletal fluorosis, which is a major
public health problem, and has socioeconomic impact, affecting millions of people
in various regions of Africa, China, and India.
Fluoridation of public drinking water in the United States was initiated more
than 50 years ago. Since then, a number of adverse effects have been attributed to
water fluoridation. At the level of 1 mg/L, F impairs the production of collagen in
the organism. It causes decomposition of collagen and results in osteoporosis, bone
tumors, fragility of bones and teeth, and also destroys connective tissues, which keep
the organism in proper position.
The possible relationship between serum Pb levels in children and chemicals
used to fluoridate has also been observed. Silicofluorides used to fluoridate water,
increase blood Pb levels. Long-term accumulation of F is also likely to affect thyroid
function, and may affect the pineal gland. Elevated F content of a body may also
increase risk of various cancers (Limeback 2001). Some data appear that fluoridation
of water may be a harmful procedure. With the inflow of new information the awareness of dangers associated with the overall effect of F increases, and more and more
countries give up fluoridation of drinking water (Meler and Meler 2006).
The fluoride content of most foods is low (less than 0.5 mg/kg). Rich sources of F
include tea, which concentrates F in its leaves, and marine fish, which are consumed
with their bone (Table 15.4). Foods generally contribute only 0.3–0.6 mg of the daily
intake of F. An adult male residing in a community with fluoridated water has F
intake range from 1 to 3 mg/day.
Direct contact with F can result in tissue damage. At high concentrations, F can
cause irritation and damage to the respiratory tract, stomach, and skin following
inhalation, oral, and dermal exposure, respectively. At very high F doses, fluoride can
bind with the serum calcium, resulting in hypocalcemia and possibly hypercalcemia;
the severe cardiac effects (e.g., tetany, decreased myocardial contractility, cardiovascular collapse, and ventricular fibrillation) observed at or near lethal doses are
probably due to the electrolyte imbalance. Metallic fluorides are very toxic. Organic
fluorides are generally much less toxic and are often quite harmless (ATSDR 2003).
The major source of dietary F in the U.S. diet is drinking water. When water is
fluoridated, F contents are adjusted to between 0.7 and 1.2 mg/L. The ESADDI for
F is 1.5 ± 4.0 mg/day (WHO 2004).
Fluorine gas is extremely corrosive and toxic. The free element has a characteristic pungent odor, detectable in concentrations as low as 20 μg/L, which is below