托福写作7、8课程(五)
2008-12-20来源:和谐英语
mild case of fluorosis, with faint white mottling.
The World Health Organization cautions that fluoride levels above 1.5 milligrams per liter leaves the risk for fluorosis.[34] Consumption of water exceeding 10 ppm fluoride has been shown to lead to pathological changes in bone structure, and skeletal fluorosis.[35] [36] 0.07 – 1.2 milligrams per liter of fluoride is considered to be the optimal level. A CDC evaluation concluded that prevalence of some level of fluorosis among children and adolescents in the United States had increased by from 22.8% in 1986 – 1987 to 32% in 1999 – 2002.[37] Debilitating environmental fluorosis of a portion of the population is a problem in several developing countries, where it is complicated by malnutrition. The effects of skeletal fluorosis can be slowly reversed through a reduction of fluoride intake and improved diet.[38] To protect against this health organizations in some high fluoride areas endorse providing alternative water sources, or removing fluoride from the water.[39]
The National Research Council states that children have a higher daily average intake than adults per kg of bodyweight.[29]:23 Those who work outside, or have urine problems also will drink more water. osteosarcoma, a rare bone disease affecting male children, has been associated with fluoride intake[40]. The weight of the evidence, as assessed by independent committees of experts, comprehensive systematic reviews, and review of the findings of individual studies does not support an association between water fluoridated at levels optimal for oral health and the risk for cancer, including osteosarcoma, [41] although a study described as the most rigorous yet by the Washington Post found a relationship among young male boys. The authors' adviser faced an investigation based on his dismissal of the results and an apparent conflict of interest.[42] An epidemiological connection between areas with high intake of silicofluorides and increased lead blood levels in children has been observed in areas fluoridated at the recommended dosage.[43][44] A 2007 update on this study confirmed the result and noted that silicofluorides, fluosilicic acid and sodium fluosilicate are used to fluoridate over 90% of US fluoridated municipal water supplies.[45]
Excess fluoride consumption has been studied as a factor in the following:
A weakening of bones, leading to an increase in hip and wrist fracture.[46] The National Research Council found the overall evidence "suggestive but inadequate for drawing firm conclusions about the risk or safety of exposures at [2 mg/L]", but states that fractures do seem to increase as fluoride is increased from 1 mg/L to 4 mg/L, suggesting a "continuous exposure-effect" dose-response relationship at these levels.[29]:170
Adverse effects on the kidney. Within the optimal dose, no effects are expected, but chronic ingestion in excess of 12 mg/day are expected to cause adverse effects, and an intake that high is possible when fluoride levels are around 4 mg/L.[29]:281 Those with impaired kidney function are more susceptible to adverse effects.[29]:292
Little research has been done on possible liver damage, although some studies suggest negative effects at chronic ingestion of 23 mg/day.[29]:292
Chromosomal damage and interference with DNA repair.[29]:304 Overall, the literature from in vitro and rodent studies does not indicate genotoxicity, but the in vivo human studies are inconsistent.[29]:316
Four epidemiological studies have noted a correlation between increased fluoride and low IQ.[29]:205-223 The most rigorous of these compared an area with mean water concentration of 0.36 ± 0.15 mg/L (range 0.18-0.76 mg/L) to an area with 2.47 ± 0.79 mg/L (range 0.57-4.50 milligrams per liter [mg/L]). Most of these studies did not publish important details, making them difficult to evaluate. If these correlations are caused by fluoride, the mechanism is not known, but the National Research Council speculates that effects on the thyroid could lead to poor test results.[29]:208
Inhibition of melatonin production and promotion of precocious puberty in animal studies.[47] Fluoride may have an analogous inhibitory effect on human melatonin production, as fluoride accumulates readily in the human pineal gland, the brain organ responsible for melatonin synthesis.[48]
A weakened immune system, leaving people vulnerable to the development of cancer and AIDS.[49][50]
Damage to the male reproductive system in various species.[51]
A disruption in endocrine function, especially in the thyroid.[52]
[edit] Endorsements
The American Dental Association states on their website that many prominent organizations endorse water fluoridation, including the World Health Organization, the Centers for Disease Control and Prevention, and the American Medical Association.[53]
On April 2, 1999, the U.S. Centers for Disease Control and Prevention listed water fluoridation as one of the 10 greatest public health achievements of the 20th century.[54]
[edit] Opposition
Main article: Water fluoridation opposition
Water fluoridation has been contentious for ethical, safety, and efficacy reasons.[3] Concerns include the alleged lack of available data,[28] evidence that extreme doses may cause serious health problems,[46][55][56][57][58][59][60][61][62][63][64][65][66][67] and ethical issues.[68][69][70][71] In the United States, it has been the subject of conspiracy theories alleging that fluoridation is part of a Neo-Con, "New World Order" plot to undermine the health and intelligence of the American public.[72]
[edit] Fluoridation around the world
Main article: Fluoridation by country
About 5.7% of people worldwide drink fluoridated water;[3] this includes 62.5% of the U.S. population.[10] 12 million people in Western Europe have fluoridated water, mainly in England, Spain, and Ireland. France, Germany, and some other European countries use fluoridated salt instead; the Netherlands, Sweden, and a few other European countries rely on fluoride supplements and other measures.[73] The justification for water fluoridation is analogous to the use of iodized salt for the prevention of goiters. China, Japan, the Philippines, and India do not fluoridate water.[74]
[edit] Malfunctions in equipment
Main article: Fluoride poisoning
At least 17 incidences of fluoridation equipment malfunction, and their associated deaths and poisonings, have been documented in U.S. newspapers and medical journals.[75] The largest incident occurred in Hooper Bay, Alaska in 1992. When fluoridation equipment failed, a large amount of fluoride was released into the drinking water supply and 296 people were poisoned; 1 person died.[75] 3 dialysis patients died and 6 were sickened at the University of Chicago Hospitals when the water filtration system failed on July 16, 1993. A hospital spokesperson said that the deaths and reactions “were consistent with fluoride exposure.”[75]
The World Health Organization cautions that fluoride levels above 1.5 milligrams per liter leaves the risk for fluorosis.[34] Consumption of water exceeding 10 ppm fluoride has been shown to lead to pathological changes in bone structure, and skeletal fluorosis.[35] [36] 0.07 – 1.2 milligrams per liter of fluoride is considered to be the optimal level. A CDC evaluation concluded that prevalence of some level of fluorosis among children and adolescents in the United States had increased by from 22.8% in 1986 – 1987 to 32% in 1999 – 2002.[37] Debilitating environmental fluorosis of a portion of the population is a problem in several developing countries, where it is complicated by malnutrition. The effects of skeletal fluorosis can be slowly reversed through a reduction of fluoride intake and improved diet.[38] To protect against this health organizations in some high fluoride areas endorse providing alternative water sources, or removing fluoride from the water.[39]
The National Research Council states that children have a higher daily average intake than adults per kg of bodyweight.[29]:23 Those who work outside, or have urine problems also will drink more water. osteosarcoma, a rare bone disease affecting male children, has been associated with fluoride intake[40]. The weight of the evidence, as assessed by independent committees of experts, comprehensive systematic reviews, and review of the findings of individual studies does not support an association between water fluoridated at levels optimal for oral health and the risk for cancer, including osteosarcoma, [41] although a study described as the most rigorous yet by the Washington Post found a relationship among young male boys. The authors' adviser faced an investigation based on his dismissal of the results and an apparent conflict of interest.[42] An epidemiological connection between areas with high intake of silicofluorides and increased lead blood levels in children has been observed in areas fluoridated at the recommended dosage.[43][44] A 2007 update on this study confirmed the result and noted that silicofluorides, fluosilicic acid and sodium fluosilicate are used to fluoridate over 90% of US fluoridated municipal water supplies.[45]
Excess fluoride consumption has been studied as a factor in the following:
A weakening of bones, leading to an increase in hip and wrist fracture.[46] The National Research Council found the overall evidence "suggestive but inadequate for drawing firm conclusions about the risk or safety of exposures at [2 mg/L]", but states that fractures do seem to increase as fluoride is increased from 1 mg/L to 4 mg/L, suggesting a "continuous exposure-effect" dose-response relationship at these levels.[29]:170
Adverse effects on the kidney. Within the optimal dose, no effects are expected, but chronic ingestion in excess of 12 mg/day are expected to cause adverse effects, and an intake that high is possible when fluoride levels are around 4 mg/L.[29]:281 Those with impaired kidney function are more susceptible to adverse effects.[29]:292
Little research has been done on possible liver damage, although some studies suggest negative effects at chronic ingestion of 23 mg/day.[29]:292
Chromosomal damage and interference with DNA repair.[29]:304 Overall, the literature from in vitro and rodent studies does not indicate genotoxicity, but the in vivo human studies are inconsistent.[29]:316
Four epidemiological studies have noted a correlation between increased fluoride and low IQ.[29]:205-223 The most rigorous of these compared an area with mean water concentration of 0.36 ± 0.15 mg/L (range 0.18-0.76 mg/L) to an area with 2.47 ± 0.79 mg/L (range 0.57-4.50 milligrams per liter [mg/L]). Most of these studies did not publish important details, making them difficult to evaluate. If these correlations are caused by fluoride, the mechanism is not known, but the National Research Council speculates that effects on the thyroid could lead to poor test results.[29]:208
Inhibition of melatonin production and promotion of precocious puberty in animal studies.[47] Fluoride may have an analogous inhibitory effect on human melatonin production, as fluoride accumulates readily in the human pineal gland, the brain organ responsible for melatonin synthesis.[48]
A weakened immune system, leaving people vulnerable to the development of cancer and AIDS.[49][50]
Damage to the male reproductive system in various species.[51]
A disruption in endocrine function, especially in the thyroid.[52]
[edit] Endorsements
The American Dental Association states on their website that many prominent organizations endorse water fluoridation, including the World Health Organization, the Centers for Disease Control and Prevention, and the American Medical Association.[53]
On April 2, 1999, the U.S. Centers for Disease Control and Prevention listed water fluoridation as one of the 10 greatest public health achievements of the 20th century.[54]
[edit] Opposition
Main article: Water fluoridation opposition
Water fluoridation has been contentious for ethical, safety, and efficacy reasons.[3] Concerns include the alleged lack of available data,[28] evidence that extreme doses may cause serious health problems,[46][55][56][57][58][59][60][61][62][63][64][65][66][67] and ethical issues.[68][69][70][71] In the United States, it has been the subject of conspiracy theories alleging that fluoridation is part of a Neo-Con, "New World Order" plot to undermine the health and intelligence of the American public.[72]
[edit] Fluoridation around the world
Main article: Fluoridation by country
About 5.7% of people worldwide drink fluoridated water;[3] this includes 62.5% of the U.S. population.[10] 12 million people in Western Europe have fluoridated water, mainly in England, Spain, and Ireland. France, Germany, and some other European countries use fluoridated salt instead; the Netherlands, Sweden, and a few other European countries rely on fluoride supplements and other measures.[73] The justification for water fluoridation is analogous to the use of iodized salt for the prevention of goiters. China, Japan, the Philippines, and India do not fluoridate water.[74]
[edit] Malfunctions in equipment
Main article: Fluoride poisoning
At least 17 incidences of fluoridation equipment malfunction, and their associated deaths and poisonings, have been documented in U.S. newspapers and medical journals.[75] The largest incident occurred in Hooper Bay, Alaska in 1992. When fluoridation equipment failed, a large amount of fluoride was released into the drinking water supply and 296 people were poisoned; 1 person died.[75] 3 dialysis patients died and 6 were sickened at the University of Chicago Hospitals when the water filtration system failed on July 16, 1993. A hospital spokesperson said that the deaths and reactions “were consistent with fluoride exposure.”[75]
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