The introduction of man-made chemicals to increase food production, protect it from insects, and increase its "shelf life" has added 60 micrograms a day of man-made chemicals to the average human diet.

The whale oil lamps of the Eskimos were so smoky that their lungs became distinctly black from carbon deposits.

Endogenous material within water supplies and even radioactivity in water exposed man to hazards.

(The word "hazard" should be considered here in context ; not infrequently, areas became popular as "spas" because of these waters - for example, Baden-Baden, which became famous for the "curative" radioactivity of its natural elements).

In the city, because of the height of its buildings, the narrowness of the streets, and waste material poured by its inhabitants, the air becomes stagnant, turbid, thick, misty, and foggy.

If there is no choice in this matter, if we have grown up in the cities and become accustomed to them, we should make an attempt to at least to dwell out at the outskirts of the city.

Wherever the air is altered ever so slightly you will find men develop dullness of understanding, failure of intelligence, and defects of memory.

Man inhales, bathes in, and eats a variety of chemical materials that are found as contaminants in foods and in the food chain, the water supply, and the general ecosystem in which he lives.

In the last two decades man-made contamination and the effects of these chemicals have caused considerable alarm. Recent attempts to quantitate the potency of environmental contaminants and to estimate past and present human exposure suggest that naturally occurring chemicals pose a far greater hazard than man-made products .

Our natural environment is not without risk, and even oxygen can be harmful.

There are several important mechanisms that govern the effect of toxic agents, including the toxin’s absorption, distribution, metabolism, and excretion.

Absorption (whether through pulmonary, gastrointestinal, or dermal routes) depends in part on the chemical structure of the agent. For example, because of their solubility in lipids the insecticides chlordane and heptachlor are rapidly absorbed and stored in body fat. By contrast, the herbicide paraquat, because it is water soluble, is readily eliminated.

The effects of many chemicals are exerted by their metabolic products rather than by the parent compound. The capacity of the xenobiotic systems to modify these materials varies among tissues. These detoxifying systems may produce different metabolites in different sites, which may vary in their capacity to produce disease. The cellular content of these enzyme systems varies with age, sex, hormonal and nutritional status, and previous drug intake.

The storage, distribution, and excretion of these materials control their concentrations in the organism at any given time.

It follows that agents stored in adipose tissue exert a prolonged low-level effect, whereas the more water-soluble materials that are easily excreted by the kidney have a shorter duration of action.

It is worth pointing out that the fact that a toxic agent can be detected in the workplace does not mean that it necessarily produce disease.

For example, carbon tetrachloride, a recognized species-dependent hepatotoxin, is used frequently in the machining of steel.  Yet liver disease derived from this haloalkaline is not an occupational hazard in the steel fabricating industry.   

Beginning with the industrial revolution there have been a  rise in the number of chemicals manufactured and a corresponding increase in the risk of human exposure.

This potential problem has elicited widespread public concern, and has particularly attracted the attention of journalists and attorneys.

It is crucial to differentiate between the problems of acute poisoning and chronic toxicity.One must also distinguish industrial and accidental exposure from that which is likely to occur in the general environment.

Except for certain hypersensitivity reactions in susceptible individuals, acute poisoning by environmental chemicals does not pose a threat to the general population.

The concentrations necessary to cause acute functional disorders or structural damage are ordinarily encountered only in the work place or as a consequence of uncommon accidents.

Although accidental mass poisonings with the pesticides endrin and parathion have led to as many as 100 deaths in a single event, no chronic sequelae among the survivors have been documented.

Despite claims of an association between progressive chronic disease and exposure to pesticides, the small number of cases together with the nonspecific nature of the complaints, does not permit such a conclusion.

It should be stressed that the action of most environmental toxins is specific, and that a causal relationship to disease implies damage to a specific organ or organ system, with specific alterations of these tissues.