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Toxicology and Drinking Water Contaminants
The author finds it difficult to believe that the chloroform levels present in drinking water constitute a health hazard. The Natl. Cancer Inst. (NCI) reported chloroform to be carcinogenic in mice and rats when administered by mouth. The tumors occurred in highly debilitated animals, resulting from the use of a maximal tolerated chloroform dose to which significant numbers of the test animals succumbed and the survivors ended up in an unhealthy condition. On the other hand, feeding experiments conducted in another laboratory involving chloroform in lower doses (one sixth to one eighth those at the NCI) yielded no malignancies in mice. In addition, no dogs developed liver tumors after 7.5 years of exposure to 30 mg/kg/day of chloroform. Thus, chloroform must be regarded as an animal carcinogen of extremely low potency.
Extrapolating animal data to man for the purpose of estimating the incidence of cancer in human populations can prove a fallacy. Biologic response to a toxic agent is not the same at low and high dosages—an assumption made by data extrapolators. The body has built‐in antagonists that can counteract the toxicity of foreign substances, including potential carcinogens. Natural and dietary sources of anticarcinogens also exist. Instances are cited where thresholds for cancer production have been demonstrated in animals and man. The threshold for tumor formation in rat livers ranges between 10 and 50 ppm in air of vinyl chloride. The incidence of liver tumors in vinyl chloride workers is extremely low and may be based genetically on inborn errors of metabolism.
Toxicology and Drinking Water Contaminants
The author finds it difficult to believe that the chloroform levels present in drinking water constitute a health hazard. The Natl. Cancer Inst. (NCI) reported chloroform to be carcinogenic in mice and rats when administered by mouth. The tumors occurred in highly debilitated animals, resulting from the use of a maximal tolerated chloroform dose to which significant numbers of the test animals succumbed and the survivors ended up in an unhealthy condition. On the other hand, feeding experiments conducted in another laboratory involving chloroform in lower doses (one sixth to one eighth those at the NCI) yielded no malignancies in mice. In addition, no dogs developed liver tumors after 7.5 years of exposure to 30 mg/kg/day of chloroform. Thus, chloroform must be regarded as an animal carcinogen of extremely low potency.
Extrapolating animal data to man for the purpose of estimating the incidence of cancer in human populations can prove a fallacy. Biologic response to a toxic agent is not the same at low and high dosages—an assumption made by data extrapolators. The body has built‐in antagonists that can counteract the toxicity of foreign substances, including potential carcinogens. Natural and dietary sources of anticarcinogens also exist. Instances are cited where thresholds for cancer production have been demonstrated in animals and man. The threshold for tumor formation in rat livers ranges between 10 and 50 ppm in air of vinyl chloride. The incidence of liver tumors in vinyl chloride workers is extremely low and may be based genetically on inborn errors of metabolism.
Toxicology and Drinking Water Contaminants
Stokinger, Herbert E. (author)
Journal ‐ American Water Works Association ; 69 ; 399-402
1977-07-01
4 pages
Article (Journal)
Electronic Resource
English
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