Carcinogenic Chemicals distribution

Nature, Distribution, and Sources of Carcinogenic Chemicals in the Environment... 

Radioactive substances (radionuclides) are known health hazards that emit energetic waves and/or particles that can cause both carcinogenic and noncarcinogenic health effects. Radionuclides pose unique threats to source water supplies and chemical processing, storage, or distribution systems because radiation emitted from radionuclides in chemical or industrial waste systems can affect individuals through several pathways by direct contact with, ingestion or inhalation of, or external exposure to, the contaminated waste stream. While radiation can occur naturally in some cases due to the decay of some minerals, intentional and nonintentional releases of... 

Kraybill, H.F. Distribution of chemical carcinogens in aquatic environments. Prog. Exp. Tumor Res. (1976) 20, 3-3. ... 

EHC monographs examine the physical and chemical properties and analytical methods sources of environmental and industrial exposure and environmental transport kinetics and meta-bohsm including absorption, distribution, transformation, and elimination short- and long-term effects on animals, carcinogenicity, mutagenicity, and teratogenicity and finally, an evaluation of risks for human health and the effects on the environment. 

Cumulative distributions of the logarithms of NOELs were plotted separately for each of the stmcmral classes. The 5th percentile NOEL was estimated for each stmctural class and this was in mrn converted to a human exposure threshold by applying the conventional default safety factor of 100 (Section 5.2.1). The stmcmre-based, tiered TTC values established were 1800 p,g/person/ day (Class I), 540 pg/person/day (Class II), and 90 pg/person/day (Class III). Endpoints covered include systemic toxicity except mutagenicity and carcinogenicity. Later work increased the number of chemicals in the database from 613 to 900 without altering the cumulative distributions of NOELs (Barlow 2005). 

One of the more important classes of chemical carcinogens are N-nitrosamines. They are important because practically all of the simple nitrosamines are carcinogenic, they are widely distributed in our environment and can be formed in the stomach from secondary and tertiary amines and the ubiquitous nitrite ion. Moreover, nitrosamines are very organ-specific. Thus, a given nitrosamine will produce a liver or an esophageal tumor, regardless of the route of administration of the carcinogen. This fact makes nitrosamines very useful in the study of mechanisms of tumor induction (1). 

There are almost no data available concerning the pharmacokinetics (i.e., the uptake, distribution, metabolisms, and excretion) of chemical carcinogens in humans. Nevertheless, it is possible to make limited assumptions about the pharmacokinetics of carcinogens, based on the results of animal studies conducted with various chemicals, notably polycyclic hydrocarbons such as benzo[a]p3nene. 

Only a small proportion of natural pesticides have been tested for carcinogenicity, but 38 of the 72 tested are rodent carcinogens. As shown in Table 2, naturally occurring pesticides that are rodent carcinogens are ubiquitous in common fruits, vegetables, herbs, and spices. The widespread distribution of such chemicals means that no diet can be free of natural chemicals that are rodent carcinogens. 

PCBs are so chemically inert that they were extensively used as heat transfer fluids in large electrical transformers, along with other uses. Of course, when they escaped into the environment, they exhibited the two troublesome qualities of persistence and biomagnification. Because PCBs are now suspected carcinogens, they are no longer manufactured in the United States. However, they are now widely distributed in the environment. Furthermore, there is the problem of disposing of the large number of electrical devices that contain these compounds. 

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