Our dazzling technological progress since World War II has yielded a random harvest of mixed blessings, and a bumper crop of new health challenges. These challenges differ from our traditional health concerns in a number of significant ways. For one thing, the nature of the assault on the human organism is very different. The public health professions are familiar with the infectious disease pattern-exposure, followed at a predictable interval by recognizable symptoms, generally followed by recovery and some degree of residual immunity. The time-span between exposure and onset is short. The effect is comparatively easy to trace to its cause.
By contrast, the chronic diseases may have multiple causes, some intrinsic but often involving one or many environmental factors. We are concerned here, not primarily with acute illness but with the slow accumulation of toxic chemicals or radiations over a period of years. The symptoms which finally develop may be identical with those resulting from non-environmental causes; radiation-induced leukemia, for example, shows no detectable difference from leukemia unrelated to radiation exposure. For these reasons, absolute proof of cause is difficult to establish within the limits of our present knowledge. And yet there is abundant evidence, both from the laboratory and from epidemiological studies, which indicates that a relationship must exist. The hazard to the individual seems to be related to the cumulative total of radiations or chemical toxicants received continuously or intermittently throughout his life span, regardless of their source.
* Presented at the Fifty-third Annual Meeting of the Air Pollution Control Association, Cincinnati, Ohio, May 24, 1960.
Some Hundreds of new chemicals find new uses in American industry annually. These may be new plastics, plasticizers, or additives to alloys, fuels or foods; they may be pesticides, preservatives, solvents, detergents, adhesives or abrasives; or they may be part of the composition of fabrics used for clothing, household draperies and kitchen equipment. Many of these materials come into intimate contact with the people of the nation in their places of work, in their conveyances to and from work, and in their homes. Many of them enter directly into the food of the land, and many others find their way indirectly into the food, the water supply and the atmosphere. In these and other ways the chemicals find their way into the midst of the already complicated chemical reaction mass of the living human body. In speaking of the chemistry of life, one is aware of certain complexities which have been revealed only partially and superficially by biochemical and physiological research. Man is composed in some part of the elements and substances that enter into the composition of the earth. The contributions made by certain mineral elements alone to the mechanisms of life have been investigated at length, but our general knowledge is but fragmentary and often fortuitous. Nevertheless, we endure our ignorance with a certain philosophical equanimity in recognition of the fact that the composition of the earth and the composition of man exist in an intimate historical and biological relationship which is inevitable and not of our making. But what can one think of the artificial situation, in which many new materials, possessed of many, almost an infinity of, possibilities for metabolic modification within the body of man, find their way into it, for better or worse. We shall never be able to anticipate and visualize the harmful potentialities of new materials until we achieve a comprehensive understanding of the role of the normal elements and other components of the living organism. Only on such a comprehensive background can we discover, fairly promptly, the metabolic deviations, if any, induced by new chemicals.
This brings us to consider the foregoing problem from a somewhat different viewpoint. No principle of biology is clearer than that which relates a physiological response to a quantity of stimulus within appropriate limits of time. The living organism is resistant in varying degree, to varying stimuli, and the stimulus must be adequate to induce a response. It is this principle on which we base the differentiation of harmful versus harmless stimuli in terms of dosage and time. Toxicity, in these terms, does not relate to a specific substance but to a concentration of that substance arrived at within certain limits of time in the effective tissue or chemical system within an organism. A toxic environment, by the same token, is one which, again within certain limits of time, introduces into the organisms a harmful quantity of a substance. The means by which this is done may be single or multiple - that is, the medium may be the atmosphere, water or food, or any combination of these. The multiple environmental sources of human exposure to chemicals provide a good illustration of the complexities of the problem of public safety. Let us look at such a situation as it relates to a mineral constituent of the earth.
A mineral taken from the earth and brought into commercial use, may pose certain problems of industrial health, from the aspect of the toxicity of one or more of its ingredients. Measures of control can be provided on the basis of certain toxicologic facts, and certain products can be made available in the desired form or forms of commerce, without undue industrial hazard. In the process, constituents of the mineral have been discharged into the air around the production factory. These settle out on the land, thereby increasing its content of the mineral in question. Vegetation which grows out of such soil may take up the mineral from the soil, and the mineral may also be deposited upon the vegetation, which then, if eaten by animals or men, carries more than its natural content of such minerals into their bodies. Such domestic animals and animal products, used as human food, contribute to the total intake of the mineral by man.
At the same time, water-borne waste from the factory is conveyed away in pipes or ditches. This pollutes a stream nearby and affects an entire drainage area to an extent which may be only theoretical on the one hand, or highly significant on the other.
This process, in one form or another, may be multiplied in many or all parts of a country, so that a mineral constituent, brought forth out of the earth, comes to be spread far and wide in the air, in the water and in the food materials of animals and men over a continent, or even over the world. This same process, multiplied still further by the industry, agriculture and other activities of a country, may so change the balance of nature, with respect to the numbers of the normal constituents of the earth and their proportional representation in the soil, water and atmosphere of the country, as to alter the mineral metabolism of mankind in the area concerned.
The illustration which we have chosen is only one of many that could be taken to follow the course of technologic man in his efforts to make use of the materials of the earth for his own purposes, to wrest from nature secrets that will feed, clothe and house her growing population, that will transport them with ever increasing speed to the four corners of the earth and beyond, and release energy from natural sources and direct it to carry out his bidding. In doing these many things, as has been pointed out elsewhere in great detail, man has changed and is changing further the face of the earth, has altered and is further disturbing the conditions under which life on this planet came into existence and has persisted, with changes and differentiation, for some millions of years. It seems likely that man's activities in strictly modem times, as represented in his technologic applications of the natural sciences, have brought about greater environmental changes of more profound physiological significance than have all the generations of men heretofore. During the greater part of historical times man has been contending with natural forces and natural threats to his survival. He has now moved into a period in which his knowledge and power have enabled him to modify the very conditions of his life. The time has come, however, when a much greater and more comprehensive knowledge of the consequences of our changed and changing environment must be had for our safety-perhaps for our very survival.
The efforts made to obtain the necessities of life and then to seek comfort, wealth and power have occupied most of the men of our time and every other time. The men of all ages, who have sought by the methods of their time to cultivate and protect the health of the people, have been few and their resources relatively small. The technology of our time has created a wealth of materials and made available the forces of nature for man's use. At the same time it has failed to bring to these materials and forces the understanding of their biological effects that will keep them under adequate control. The effort must be made to reduce the gap between technology and biology before it is too late. This will take time, studious effort and money: time for the training of experts in the various fields of medicine, hygiene and sanitation; studious effort to ferret out the problems most in need of investigation; money to initiate and catalyze the investigations without which we shall remain in relative ignorance.
It must become an axiom of modern chemical and technologic research that the materials produced and the forms of energy harnessed must be as well understood for their biological potentialities as for their physical and mechanical properties. It is equally important that other man-made factors in the human environment, including those which we cannot foresee at this time, should be examined critically for their harmful potentialities, in the full recognition of certain facts of life and death, which have recently come upon some of us with a shock. It is clear that reckless man can turn loose and build up physical forces which may destroy himself and his kind. It seems probable, however, that the same ingenuity which thus far has enabled him to explore and to penetrate other secrets of nature, will serve his need when expended in learning more of his own vulnerability and in developing the means for self-protection.
* * * * * * * * * * * * * * * * *
From The Proceedings of the Conference on "Man Versus Environment," May 5-6, 1958, published with support by the U. S. Public Health Service, Department of Health, Education, and Welfare.
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