Genotoxic carcinogens chemicals

Some chemicals are believed to have no threshold above which toxic effects are observed. In other words, a single molecule has the potential to induce an adverse effect. The most common group of hazards in this respect are genotoxic carcinogens. Chemical carcinogens are not normally approved as food additives because an acceptable daily intake cannot be established. 

HCFC-141b is a colorless, volatile liquid with a weak, ethereal odor. The vapor is heavier than air and can displace air in confined spaces. Additional chemical and physical properties are listed in Table 4-2. Experimental studies with human subjects and several mammalian species (monkey, dog, rat, mouse, and rabbit) were located. Animal studies addressed both acute and chronic exposure durations as well as neurotoxicity, genotoxicity, carcinogenicity, and cardiac sensitization. 

Ashby, J. and Tennant, R.W. (1988). Chemical structure, Salmonella mutagenicity and extent of carcinogenicity as indices of genotoxic carcinogens among 222 chemicals tested in rodents by the US NCI/NTP. Mutation Res. 204 17-115. 

Eor most of the toxic effects that might be exerted by a chemical substance, including at least certain types of genotoxic carcinogenicity, the dose-response curve is S-shaped as illustrated in Eigure 4.1 where the carcinogenic response is the mmor incidence. This means that no or only a few tumors occur at the lower dose levels, but the mmor incidence increases as the dose level increases, in many cases until a plateau is reached. 

In the effects assessment step the relationship between the level of exposure and the incidence, nature, and severity of an (adverse) effect following the exposure is determined. For most types of effects, it is assumed that there is a minimum dose or concentration below which adverse effects will not occur the no effect level or threshold. To determine the threshold, different doses are tested, for most chemical hazards usually in laboratory animals. In toxicology, the highest tested dose without adverse effects is called the no observed adverse effect level (NOAEL). Based on the NOAEL established in an experimental study, a human limit value can be calculated, taking into account uncertainties and differences in experimental design and circumstances. Uncertainties and differences are accounted for by uncertainty factors (e.g., for interspecies differences, intraspecies variability, and exposure duration). For some types of substances, it is assumed that every level of exposure can result in adverse effects, in which case no threshold would exist. This, for instance, is assumed to apply for genotoxic carcinogens. 

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