Monitoring and Control of Hazards

The complex mixture of chemicals that constitute food, together with the uncertainty of the specific role of the various components in the diet, has made the control of potential carcinogens in food difficult. In particular, the realization that animal carcinogens, as identified by standard animal bioas-says, are widely distributed in the general environment, including food, has made control by total elimination impossible.

Control of toxic agents in food particularly contaminants and additives has been achieved by examining their hazard in animal studies. Thus, the establishment of a no-observable-adverse-effect-levels (NOAEL) is followed by the setting of an allowable daily intake (ADI) through extrapolation based on the relative sensitivity of animals and humans to toxic events. This extrapolation may also take into consideration other properties of the chemical concerned, such as genotoxic potential. For genotoxic carcinogens, however, it is generally considered that there is no no-effect-level and therefore acceptable intake is based on estimation of likely risk. A maximum risk of 10~6 cancers in a lifetime is considered as an acceptable risk by some authorities, particularly those in the US, and acceptable exposure estimates extrapolated from animal data. For nongenotoxic carcinogens (and for some geno-toxic carcinogens, particularly those that act as aneugens), no-effect levels are accepted, since the carcinogenic response is the result of a prior toxic event for which a no-effect-level can be determined. For additional safety, an arbitrary factor of 100 was applied to the NOAEL, to allow for interspecies variation (x10) and interindividual variability (x10). More recently, the two factors have been subdivided into variable factors (pharmacokinetic and pharmacodynamic) to reflect increased understanding of the mechanisms underlying the development of cancer and allow for factors associated with special groups such as infants and children. It must be said that the scientific basis to support either of these approaches (acceptable risk or no-effect-levels) is quite limited as even for the best-documented cases, the mechanism of the carcinogenic effect is poorly understood.

The unequivocal identification of human carcinogens is difficult since direct experimental approaches are precluded. Thus, epidemiological data involving both prospective and retrospective studies, and using case controls in certain investigations, has to be employed. These techniques have limited applications to diet-associated carcinogenesis and have proved most useful in identifying specific carcinogens in the work place or those used as therapeutic agents. The specific problem in identifying dietary carcinogens relate to the complexity of diet, the difficulty in identifying specific components, and the sensitivity of the epidemiological methods themselves. It would seem likely that epidemiological data will only be able to link specific chemical carcinogens in food with a carcinogenic effect in a few favorable circumstances, since such chemicals are likely to be present at low levels and induce only a small increase in tumor incidence over background levels. 0ne such example was the identification of a carcinogenic hydrazone in the mushroom Gyromitra esculenta, as a result of an epidemiologi-cal study in Finland. Such methods have also indicated the relative importance of 'life style' factors in carcinogenesis: in particular, associations have been made between lack of dietary fiber and colon cancer, between a low intake of fresh fruit and vegetables and stomach cancer, and between excess dietary fat and colon and breast cancer, although the specific chemicals responsible have not been identified with any certainty.

Most of the activity aimed at controlling carcinogens in food has been directed at preventing addition of potentially carcinogenic substances to the existing background level of natural carcinogens. This has been tackled through the application of laws governing the adulteration of food, the first of which were enacted in the mid-nineteenth century in the UK. The current UK legislation is the 1990 Food Safety Act, governing the nature and quality of food and its nutritive value. This Act, like its forerunner, the 1955 Food and Drug Act, requires that the constituents of food should not be injurious to health. Thus, while there is no specific requirement for carcinogeni-city testing in the current act, consideration is given to all available data, including the result of mutageni-city tests and long-term tests in animals.

The position in the US up to 1958 was similar to that in the UK. Food was considered adulterated if injury could arise from its use. Legislation was based on traditional food, added substances, and unavoidable added substances (contaminants). For added substances, listed in an inventory of over 3000 chemicals and often referred to as 'Everything Added to Food in the United States' (EAFUS), the food was considered adulterated if the added substance could render the food injurious to health; for unavoidably added substances, a balance was applied between the essential nature of the food material and the degree of contamination. These strictures applied to both carcinogenic and noncarcinogenic toxicants. In 1958 a change in emphasis was introduced through the Food Additives Amendment. This established a licensing scheme for substances deliberately added to foods or for substances that could migrate into food, but excluded materials that were generally, through usage, regarded as safe (GRAS). For licensing purposes, the material has to be shown to be 'safe' for its intended use, although in theory at least the GRAS substance could be a carcinogen.

In 1958 the Delaney Clause was enacted; this required that if there was evidence of carcinogenicity in any test system, the material should be prohibited from food usage. Improved analytical techniques have shown that many foods contain both unintentionally added and natural carcinogens, such as polynuclear aromatic hydrocarbons, nitrosamines, mycotoxins and arylamines, and no form of regulation could control these materials. Furthermore, bulk components of food may themselves play an important role in the development of carcinogenesis. The recognition that the exclusion of all potentially carcinogenic additives (under the Delaney Clause) is a practical impossibility has given way to the concept of 'safe' tolerance, and that 'safe levels' may be set by appropriate, conservative risk assessment in which an 'insignificant life time risk' of developing tumors of, for example, 10~6 is considered acceptable.

See also: Cancer: Epidemiology and Associations Between Diet and Cancer. Fish. Food Safety: Mycotoxins. Meat, Poultry and Meat Products. Sodium: Salt Intake and Health.

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