Carcinogens original form

Chlorination can result in unacceptable taste intensification, where potable water is concerned. This often originates in the chlorination of phenols present in trace amounts from industrial pollution. If economics permit, use of chlorine dioxide (Section 12.2) or ozone (Section 8.3) in place of chlorine will minimize taste intensification and will also avoid formation of carcinogenic chlorocarbons, notably chloroform. These carcinogens may form from chlorination of contaminants such as acetone, a commonly used solvent that finds its way into water supplies ... 

It is also assumed that PAH in their original form are not carcinogenic. Through their activation, particularly during their metabolism, free radicals, epoxides and diolepoxides are formed, which are then bound, for example, to DNA (Fig. 9.6). A concept currently prevalent is that PAH are metabolized through several intermediate steps. Among the various metabolites, epoxides and diolepoxides are considered to be most dan-... 

Although ultra accelerators or sulfur donors can be used together with primary accelerator (such as sulfenamide, TBBS) to improve cure rate as well as the heat resistance [16-18], their use is restricted because of the associated nitrosamine issue [19]. Accelerators derived from secondary amines, for example, MBS, TMTD, TETD, TMTM, and OTOS fall into this category. The combination of sulfenamide, such as CBS or TBBS, and a thiuram, such as TMTD or TETD, shows high-cure rates but suffers from the adverse effects on scorch resistance and vulcanizate dynamic property [20]. Additionally as previously mentioned, the use of TMTD or Tetraethylthiuram disulhde (TETD) or A-oxidiethylene dithiocarbamyl-A -oxidiethylene sulfenamide (OTOS) or 4,4 -Dithiodimorpholine (DTDM) is undesirable [21] due to concerns over carcinogenic nature of the A-nitrosamines formed from the parent amines. The solution to this originated by introduction of nitrosamine safe ultra accelerator such as TBzTD [22,23]. 

Photoreactivation and dealkylation by enzymes that directly reverse the altered DNA structure to its original state. This form of repair has been associated mainly with microorganisms and is thought to occur in mammalian cells.1 1 3 It is not involved currently in predictive tests for carcinogenicity or mutagenicity. 

This polycyclic, aromatic hydrocarbon is produced continuously by almost all plants, irrespective of their habitat, and remains qualitatively and quantitatively constant. The normal content of the carcinogenic 3.4 -benzpyrene equals 1 pg/lOO g dried plant material. (The assumed quantity of carcinogenic polycyclic hydrocarbons ingested daily with food and drinking water is calculated at 10 ig/day.) Food of animal origin, even in roasted, smoked or grilled form, contains substantially less benzpyrene than plants do. 

Nabam was originally described in 1943. When mixed with zinc or manganese sulfate, zineb or maneb is formed, respectively. The mixed salt of zinc and manganese, mancozeb is used quite extensively. The alkyl-enebis(dithiocarbamate)s have a low mammalian toxicity (e.g., LD50 = 8000 mg/kg for rats) but are considered to be carcinogenic, notably through the metabolite ethylenethiourea, which is formed by cooking. 

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