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 Ca 10 F 2 (PO 4 ) 6 , 77% Na 3 AlF 6 , and 62%
CaF 2 are absorbed. About 50% of the absorbed F is excreted by the kidneys
while the remainder is stored, primarily in calcified tissues. No significant F
accumulation occurs in soft tissues.
Bone has a great affinity for F and incorporates it into hydroxyapatite
(Ca 10 (OH) 2 (PO 4 ) 6 ), forming fluorapatite (Ca 10 F 2 (PO 4 ) 6 ). Even at low levels of
F intake, appreciable levels of F will, in time, accumulate in calcified tissues.
The effectiveness of low levels of F intake in reducing dental caries in humans,
rats, and some other species of animals has been reported. In human
population, water supply containing 1ppm F is reported to reduce by more
than 50% dental caries incidence in individuals who consume F from infancy.
Fluoride is incorporated into tooth mineral as fluorapatite at the time of
calcification.
10.6.3 ACUTE EFFECTS
Exposure to high levels of F results in varying degrees of injuries (see for
example Case Study 10.2). 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, or approximately 50 mg/kg, a
dose similar to the LD 50 for several animal species. The cause of death is
probably related to the prompt binding of serum Ca and magnesium (Mg) by
F. Clinical symptoms include excessive salivation, perspiration, vomiting,
painful spasms of limbs, stiffness, nausea, chronic convulsion, necrosis of the
mucosa of the digestive tract, and heart failure.
CASE STUDY 10.2
A fluoride overfeed occurred in 2002 at a well site near an elementary school in
Portage, Michigan.
22 The incident resulted in a high F concentration (92 mg/l)
in the drinking water at the school. Several students who drank water from the
school fountain reportedly suffered nausea and vomiting. Toxicological studies
were conducted to assess the risk. Based on the symptoms experienced by the
students, it was concluded that the F had irritated the stomach, causing the
observed symptoms, but that no appreciable long-term adverse health effects
would occur.
23
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.
24 Coupled with other environ162
Environmental Toxicology
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-010.3d]
Ref: 4365 MING-HO YU Chap-010 Page: 162 149-170
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 Ca 10 F 2 (PO 4 ) 6 , 77% Na 3 AlF 6 , and 62%
CaF 2 are absorbed. About 50% of the absorbed F is excreted by the kidneys
while the remainder is stored, primarily in calcified tissues. No significant F
accumulation occurs in soft tissues.
Bone has a great affinity for F and incorporates it into hydroxyapatite
(Ca 10 (OH) 2 (PO 4 ) 6 ), forming fluorapatite (Ca 10 F 2 (PO 4 ) 6 ). Even at low levels of
F intake, appreciable levels of F will, in time, accumulate in calcified tissues.
The effectiveness of low levels of F intake in reducing dental caries in humans,
rats, and some other species of animals has been reported. In human
population, water supply containing 1ppm F is reported to reduce by more
than 50% dental caries incidence in individuals who consume F from infancy.
Fluoride is incorporated into tooth mineral as fluorapatite at the time of
calcification.
10.6.3 ACUTE EFFECTS
Exposure to high levels of F results in varying degrees of injuries (see for
example Case Study 10.2). 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, or approximately 50 mg/kg, a
dose similar to the LD 50 for several animal species. The cause of death is
probably related to the prompt binding of serum Ca and magnesium (Mg) by
F. Clinical symptoms include excessive salivation, perspiration, vomiting,
painful spasms of limbs, stiffness, nausea, chronic convulsion, necrosis of the
mucosa of the digestive tract, and heart failure.
CASE STUDY 10.2
A fluoride overfeed occurred in 2002 at a well site near an elementary school in
Portage, Michigan.
22 The incident resulted in a high F concentration (92 mg/l)
in the drinking water at the school. Several students who drank water from the
school fountain reportedly suffered nausea and vomiting. Toxicological studies
were conducted to assess the risk. Based on the symptoms experienced by the
students, it was concluded that the F had irritated the stomach, causing the
observed symptoms, but that no appreciable long-term adverse health effects
would occur.
23
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.
24 Coupled with other environ162
Environmental Toxicology
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-010.3d]
Ref: 4365 MING-HO YU Chap-010 Page: 162 149-170