symptoms of chlorosis and tip necrosis. Studies in 1983 showed that ambient F
concentration in the area range from 0.4 to 15 mg/kg (average, 4.5 mg/kg).
Analysis of the F content of leaves of rice plants grown in the area revealed
marked increases, and the levels were correlated with increasing severity of leaf
injury. The severely injured leaves contained 80 times as much F as the healthy
leaves. Subsequently, laboratory experiments involving fumigation of rice
seedlings with HF were conducted. The results showed leaf symptoms that
were similar to those observed in the field. These observations suggested to the
researchers that F emitted from the ceramic and brick factories was the cause of
the observed ‘‘new rice disease.’’
16
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. Common
sources of excessive F intake include: forages subjected to airborne contamination or grown in soils containing high F levels, water containing high levels
of F, and feed supplement containing high levels of F. The effect of F on
domestic animals may be acute or chronic, depending on the levels to which
animals were exposed.
10.5.2 ACUTE EFFECTS
F and arsenic (As) have caused detrimental effects on livestock in the U.S. and
several other industrialized countries. The sources of F pollution are limited
mostly to phosphate-fertilizer manufacturing, aluminum production, fluorohydrocarbons, and heavy-metal production. A safe level of soluble F in
animal rations ranges from 30 to 50 mg/kg for cattle and from 70 to 100 mg/kg
for sheep and swine. F poisoning may cause physiological effects, such as
gastroenteritis, muscular weakness, pulmonary congestion, nausea, vomiting,
diarrhea, chronic convulsions, necrosis of mucosa of the digestive tract,
anorexia, cramping, collapse, and respiratory and cardiac failure, possibly
leading to death.
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. Dental fluorosis is the first sign of chronic F
toxicity. It is exhibited by white, yellow, brown, and black discoloration of
tooth enamel, either in spots or in horizontal streaks. An affected tooth is also
Environmental Fluoride
157
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-010.3d]
Ref: 4365 MING-HO YU Chap-010 Page: 157 149-170
concentration in the area range from 0.4 to 15 mg/kg (average, 4.5 mg/kg).
Analysis of the F content of leaves of rice plants grown in the area revealed
marked increases, and the levels were correlated with increasing severity of leaf
injury. The severely injured leaves contained 80 times as much F as the healthy
leaves. Subsequently, laboratory experiments involving fumigation of rice
seedlings with HF were conducted. The results showed leaf symptoms that
were similar to those observed in the field. These observations suggested to the
researchers that F emitted from the ceramic and brick factories was the cause of
the observed ‘‘new rice disease.’’
16
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. Common
sources of excessive F intake include: forages subjected to airborne contamination or grown in soils containing high F levels, water containing high levels
of F, and feed supplement containing high levels of F. The effect of F on
domestic animals may be acute or chronic, depending on the levels to which
animals were exposed.
10.5.2 ACUTE EFFECTS
F and arsenic (As) have caused detrimental effects on livestock in the U.S. and
several other industrialized countries. The sources of F pollution are limited
mostly to phosphate-fertilizer manufacturing, aluminum production, fluorohydrocarbons, and heavy-metal production. A safe level of soluble F in
animal rations ranges from 30 to 50 mg/kg for cattle and from 70 to 100 mg/kg
for sheep and swine. F poisoning may cause physiological effects, such as
gastroenteritis, muscular weakness, pulmonary congestion, nausea, vomiting,
diarrhea, chronic convulsions, necrosis of mucosa of the digestive tract,
anorexia, cramping, collapse, and respiratory and cardiac failure, possibly
leading to death.
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. Dental fluorosis is the first sign of chronic F
toxicity. It is exhibited by white, yellow, brown, and black discoloration of
tooth enamel, either in spots or in horizontal streaks. An affected tooth is also
Environmental Fluoride
157
[16:52 26/8/04 P:/CRC PRESS/4365 MING-HO.751 (1670)/4365-010.3d]
Ref: 4365 MING-HO YU Chap-010 Page: 157 149-170