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A Practical Approach
Condensed version of a paper read in Rome, published in Natural Food and Farming, Vol. 3, No. 10, February 1957.
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The Rome Symposium had no enforcement power. It could only suggest cooperation to achieve its ends. So far as the United States was concerned, responsibility passed to the Food Protection Board of the National Research Council (which has been considering a memo on the subject for a year but has not yet acted), the Food and Drug Administration, and the National Institutes of Health, whose environmental cancer chief, Dr. W. C. Hueper, read the following paper at Rome. [Prepared by John Lear, Science Editor of The Saturday Review]
A rapidly growing number and variety of non-nutritive substances have been introduced during recent decades into foodstuffs intended for general human consumption through the use of modern methods of food production and processing. Some of these chemicals are intentionally added to foods for various reasons, while others are employed for different purposes in the production of foodstuffs and remain unintentionally in them as residues. A disturbing aspect of this development is that there exists no mandatory provision for assuring, a priori, that biologic properties of each of these additives and contaminants, particularly long term or delayed effects, have adequately been studied. The circumstances suggest the virtual certainty that many have not.
It is especially important in this respect that observations made during recent years in men and experimental animals have demonstrated a not inconsiderable number of chemicals similar to, or identical with, those introduced into foodstuffs which possess carcinogenic (cancer-provoking) properties. The actual or possible existence of cancer hazards related to carcinogens in foodstuffs therefore poses a serious public health problem. The daily and lifelong exposure to such agents would represent one of the most important of the various potential sources of contact with environmental carcinogens for the population at large.
The main groups of food additives and contaminants include natural and synthetic dyes, antioxidants of fats and lipoids and vegetable matter, thickeners, sweeteners, flavoring agents, surfactants (detergents, foaming agents), humectants (smoke agents), preservatives and chemical sterilizing agents, water conditioners (iodine, fluorides), antifoaming agents, salt substitutes, shortenings, softeners, bleaches, modifiers and improvers (meat tenderizers, etc.), oil and fat substitutes, organic solvents, emulsifiers and solidifiers, pesticide residues, antisprouting and antimaturition agents of fruits and vegetables, insect repellents, hormonal fattening agents, antibiotics (fed to food animals and added to foodstuffs), enzymes, antienzymatics, pan-glazes (silicones), pan-greases (mineral oils), water pollutants, chemical sterilizing agents, wrapping and coating materials (paraffin, waxes, resins, plastics), soot adherent to smoked foodstuff and roasted and toasted products, household detergents and their coloring agents, non-ionizing radiation (ultraviolet) products, ionizing radiation (radioactive) products, and radioactive substances taken up by plants and food animals from air, soil, or water contaminated by radioactive fall-out.
The bulk of the still rather restricted pertinent information on potential cancer hazards from these additives and contaminants is of relatively recent date. Knowledge of such observations is often limited to parties mainly interested in scientific aspects of carcinogenesis and is sometimes not fully appreciated by those parties concerned with the practical aspects of potential human cancer hazards inferable from these experimental findings.
There is no necessary relation between toxicity (poisoning now effectively prevented by food and drug laws) and carcinogenicity of chemical agents. As a rule, the minimal carcinogenic dose is distinctly lower than the minimal chronic toxic dose. It is for this reason that not infrequently carcinogenic reactions may develop upon exposure to carcinogenic chemicals without a preceding or simultaneous appearance of any toxic symptoms.
In a graduated scale of the relative significance of potential environmental carcinogenic agents from a public health viewpoint, the highest priority for carcinogenic screening should be extended to those agents with which large parts of the general population have frequent and prolonged contact, whose possible carcinogenic effects on man can least readily be ascertained, and which for this reason are most difficult to control by preventive methods. Chemicals included in this group are those which enter the general human environment of every home in the form of consumer goods, or as environmental contaminants. Agents of this type are the large group of chemical additives and contaminants of foodstuffs in addition to many environmental poisons, pollutants of water, air, and soil, household drugs, sanitary supplies, cleaning agents, polishes, paints, and cosmetics.
If one adopts the principle that the protection of the health of the general public deserves foremost attention, the following considerations may profitably be used as guidelines in arriving at intelligent and rational decisions.
- Carcinogens vary greatly in their relative potency. Coal tars of different derivations, for instance, vary greatly in their relative carcinogenic potency in man and experimental animals. Coal tars are in turn usually more potent than wood tars or vegetable tars or tars obtained in the fractionation of petroleum.
- Dose observations made in experimental animals are not directly applicable to man. There exists marked differences in potency of a particular chemical for various species.
- Repeated exposures to carcinogens produce a cumulative carcinogenic effect in the exposed tissues. Cells once exposed to a carcinogen seem to retain the entire or a considerable portion of the initial effect exerted by individual exposures, even if these by themselves may be insufficient for eliciting a neoplastic (malignant) response. Subeffectively exposed cells can be challenged into carcinogenic activity either by additional subminimal carcinogenic exposures or by contact with specific promoting chemicals.
- Actual exposure to a dietary carcinogen does not always stop with the cessation of environmental contact. Some chemicals are not metabolically destroyed or excreted but are retained in active form in certain tissues from which they may gradually be mobilized long after the environmental exposure has ceased.
- Exposure to a dietary carcinogen may be complicated by occupational, medicinal, cosmetic, sanitary, or environmental contact with the same chemical or some other chemical.
- It is perhaps possible to enforce to a reasonable degree laws concerning the maximal content and adequate purity of food additives and contaminants in foodstuffs merchandized by relatively large trade organizations dealing in large quantities in nationwide and interstate commerce and using standardized and well controlled methods of processing, handling, and shipping. Considerable difficulties in this respect may be encountered, on the other hand, regarding the proper supervision of foodstuffs produced and sold on a local level. The mere passage of laws establishing standards in such matters without providing adequate means to enforce them might produce in the population a deceptive impression of safety. The most effective method of control of health hazards of this type doubtless is found under such circumstances in a complete elimination of the dangerous agents from the human environment wherever such a procedure is possible.
- Since many foodstuffs containing artificial food additives and contaminants are not adequately labeled as to the amount and type of chemicals added to the natural food products, the general consumer is relatively rarely able to make any intelligent selection between different products of the same type, particularly between “natural” foodstuffs and “artificially modified and contaminated” ones. Indeed, in many instances, he may have little choice in such matters, because all or nearly all foodstuffs of certain types which he is able to purchase are of the contaminated or modified variety. The consumer under such circumstances is a member of a “captive” population which may be subjected to potential, long delayed health hazards which he has neither consented to nor is able to avoid. For these reasons the general public is entitled to expect that all chemical additives and contaminants are subjected to comprehensive and thorough studies for toxic, carcinogenic, and cocarcinogenic properties before they are used or introduced in human foodstuffs.
It is unlikely from an application of our present knowledge of environmental carcinogens that many of the presently used additives and contaminants of foodstuffs introduce any carcinogenic hazard into the general food supply and, therefore, deserve any immediate attention. The large number of additives as well as the complexity and costliness of the biologic testing for carcinogenic properties of any one of them, moreover, precludes for merely practical reasons any large-scale attack of the problem on the entire front at the present time. It is quite obvious that under the existing conditions a step-by-step procedure will have to be adopted and that investigative efforts would best be expended for the time being on those circumscribed groups of chemicals which from the already available information have furnished carcinogenic or cocarcinogenic agents, i.e., synthetic dyes, chlorinated pesticides, animal and plant hormones, and detergents.
Among the various formerly and presently used synthetic food dyes, carcinogenic properties were discovered during recent years in a surprisingly large number when tested in rats and mice. Rodent cancers have also been produced by chemical compounds of the same stilbene family which has recently been introduced as coloring matter in many household detergents used for the cleaning of kitchen utensils, dishes, and cooking equipment of homes and commercial eating places.
Potential carcinogenic contaminants also may be introduced into foodstuffs if vegetables, fruits, fish, oysters, and livestock are grown on soil or in water polluted with known carcinogens, such as radioactive matter, arsenicals, selenium and polycyclic hydrocarbons contained in ship fuel oils. Consideration, moreover, must be given to the possibility that carcinogenic chemicals may be formed from noncarcinogenic ones under the influence of heat. Possible examples are (1) charred or tarry carbonaceous matter formed when bread or biscuits are excessively toasted or meats are grilled or roasted or (2) hydrocarbon constituents of mineral oils freed by cracking of the oil when it is used as a fat substitute and subjected to heat during grilling or baking.
There exists also the possibility that original noncarcinogenic additives and contaminants may interreact with each other or with food constituents and form new compounds possessing carcinogenic properties in the foodstuffs. They may be produced under the influence of processing procedures or during the preparation of food in the kitchen. Plastics used as wrapping material, sausage skins and coating material of fruits, cheese, meat, butter, and can linings may carry a similar hazard.
Mention may finally be made of several experimental observations indicating that a dietary intake of certain species of alkaloids which contaminate foodstuffs (chilies, alkaloids of senecio plants, crude ergot) may result in the development of liver tumors when given to rats.
The use of various types of radiating energy in the processing of foodstuffs also deserves consideration from a carcinogenic viewpoint, since these agents (ultraviolet radiation, ionizing radiation) produce in the constituents of food, such as sterols and nucleoproteins, definite chemical changes. No reliable information exists and no adequate experimental studies have been made for establishing the noncarcinogenic nature of the radiation products, although both types of radiation are eminently carcinogenic when acting on living tissues of both man and various species of animals.
The great majority of the different cancerous reactions mentioned here were produced either by the administration of excessively high doses or followed upon their introduction through routes distinct from those encountered under ordinary alimentation. The cancers developed in animals differed in various metabolic respects from man. But the mere fact of the existence of such responses presents a definite warning deserving serious attention if possible endemic and epidemic cancerous manifestations among exposed population groups are to be avoided.