Toxic agents carcinogens

Epidemiology studies are, of course, useful only after human exposure has occurred. For certain classes of toxic agents, carcinogens being the most notable, exposure may have to take place for several decades before the effect, if it exists, is observable - some adverse effects, such as cancers, require many years to develop. The obvious point is that epidemiology studies cannot be used to identify toxic properties prior to the introduction of a chemical into commerce. This is one reason toxicologists were invented ... 

Airborne particulate matter may be associated with many carcinogenic and other toxic agents. Hazardous materials include coal dust, fly-ash from power stations, metals and metal oxides from mining, extraction and refining and materials used as catalysts in industrial processes, as well as particulate matter from, for example, diesel exhausts. 

Stenhack F, Shuhik P Lack of toxicity and carcinogenicity of some commonly used cutaneous agents. Toxicol Appl Pharmacol 30 7-13, 1974... 

Toxic and carcinogenic agents in dry NT610 and moist snuff. J Nat Cancer Inst 1987 79(6) 1281-1286. 

This equation is a fairly typical biological structure-activity relationship with a strong dependence on partition coefficients, and it therefore suggests that the nitrosamines, and perhaps other chemical carcinogens as well, are similar - in the pharmacological sense - to analgesics or toxic agents. 

The National Toxicology Program performed a subchronic study of CN to generate data on the maximally tolerated dose (MTD) of this agent preparatory to launching a full-scale chronic-toxicity and carcinogenicity bioassay.38 The test was conducted in Fischer 344... 

The toxicity and carcinogenicity of N-alkyl-N-nitroso compounds depend on the formation in vivo of one or more species of alkylating agent, i.e., diazoalkanes, carbonium ions, or both [24]. They are believed to be activated by CYP2A6 via a-hydroxylation, as shown in the scheme below ... 

The exposure of experimental animals to toxic agents in high doses is a necessary and valid method of discovering possible carcinogenic hazards in humans. 

Synonym iodomethane Formula CH3I MW 142.94 CAS [74-88-4] used as a methylating agent and in microscopy colorless liquid, turns yellow or brown on exposure to light or moisture boils at 42.5°C vapor pressure 375 torr at 20°C freezes at -66.5°C decomposes at 270°C density 2.28 g/mL low solubility in water (2%) soluble in alcohol and ether toxic and carcinogenic. 

Individuals of the same species may differ significantly in their susceptibilities to various toxic agents. These differences are often genetic in nature. For example, some individuals lack tumor suppressor genes that other individuals possess and are thus more likely to develop some kinds of cancers, some of which are initiated by carcinogens. With increased knowledge of the human genome, these kinds of susceptibilities may become more apparent and appropriate preventive measures may be applied in some cases. 

Dioxin is a common name for dibenzo-l,4-dioxane, which is 1,4-dioxane fused with two benzene rings. The name dioxin is often used incorrectly in the news media for 2,3,7,8-tetrachlorodibenzodioxin (TCDD), a toxic contaminant in the synthesis of the herbicide called 2,4,5-T or Agent Orange. Surprisingly, TCDD has been in the environment for many millions of years because it is also formed in forest fires. Most dioxins are toxic and carcinogenic (cause cancer) because they associate with DNA and cause a misreading of the genetic code. 

Hydrazine, NH2NH2, is a powerful reducing agent (E° = —1.16 V) in addition, its nitrogenated reaction product is the harmless and environmentally safe N2. A disadvantage is that NH2NH2 is toxic (possibly carcinogenic). Consequently, it is used primarily in closed circuits. 

Safety Note. Because acyclic triazenes are potent biological alkylating agents, it is only prudent to assume that triazolines are also potentially toxic and carcinogenic. Efficient hoods and protective clothing should be used in working with these substances. Alkyl azides are treacherously explosive and should be treated with extreme caution. Wherever possible these compounds should only be handled as solutions. 

Chronic studies include one additional end point of toxicity any carcinogenicity related to exposure to the test agent. Traditionally, and mainly because tumor formation is seen in older animals, carcinogenicity studies in rodents are conducted for an 18 or 24 month period for mice and rats, respectively, separate from the shorter-term, 6 month chronic studies. The dosage range used for carcinogenic assessment is lower than that used for chronic toxicity... 

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