environment, a drastic change has come about in the nature of the most serious public health
problems. Only yesterday mankind lived in fear of the scourges of smallpox, cholera, and plague
that once swept nations before them. Now our major concern is no longer with the disease
organisms that once were omnipresent; sanitation, better living conditions, and new drugs
have given us a high degree of control over infectious disease. Today we are concerned with a
different kind of hazard that lurks in our environment—a hazard we ourselves have introduced
into our world as our modern way of life has evolved.
The new environmental health problems are multiple—created by radiation in all its forms,
born of the never-ending stream of chemicals of which pesticides are a part, chemicals now
pervading the world in which we live, acting upon us directly and indirectly, separately and
collectively. Their presence casts a shadow that is no less ominous because it is formless and
obscure, no less frightening because it is simply impossible to predict the effects of lifetime
exposure to chemical and physical agents that are not part of the biological experience of man.
‘We all live under the haunting fear that something may corrupt the environment to the point
where man joins the dinosaurs as an obsolete form of life,’ says Dr. David Price of the United
States Public Health Service. ‘And what makes these thoughts all the more disturbing is the
knowledge that our fate could perhaps be sealed twenty or more years before the
development of symptoms.’ Where do pesticides fit into the picture of environmental disease?
We have seen that they now contaminate soil, water, and food, that they have the power to
make our streams fishless and our gardens and woodlands silent and birdless. Man, however
much he may like to pretend the contrary, is part of nature. Can he escape a pollution that is
now so thoroughly distributed throughout our world?
We know that even single exposures to these chemicals, if the amount is large enough, can
precipitate acute poisoning. But this is not the major problem. The sudden illness or death of
farmers, spraymen, pilots, and others exposed to appreciable quantities of pesticides are tragic
and should not occur. For the population as a whole, we must be more concerned with the
delayed effects of absorbing small amounts of the pesticides that invisibly contaminate our
world. Responsible public health officials have pointed out that the biological effects of
chemicals are cumulative over long periods of time, and that the hazard to the individual may
depend on the sum of the exposures received throughout his lifetime. For these very reasons
the danger is easily ignored. It is human nature to shrug off what may seem to us a vague threat
of future disaster. ‘Men are naturally most impressed by diseases which have obvious
manifestations,’ says a wise physician, Dr. René Dubos, ‘yet some of their worst enemies creep
on them unobtrusively.’ For each of us, as for the robin in Michigan or the salmon in the
Miramichi, this is a problem of ecology, of interrelationships, of interdependence. We poison
the caddis flies in a stream and the salmon runs dwindle and die. We poison the gnats in a lake
and the poison travels from link to link of the food chain and soon the birds of the lake margins
become its victims. We spray our elms and the following springs are silent of robin song, not
because we sprayed the robins directly but because the poison traveled, step by step, through
the now familiar elm leaf-earthworm-robin cycle. These are matters of record, observable, part
of the visible world around us. They reflect the web of life—or death—that scientists know as
ecology.
But there is also an ecology of the world within our bodies. In this unseen world minute causes
produce mighty effects; the effect, moreover, is often seemingly unrelated to the cause,
appearing in a part of the body remote from the area where the original injury was sustained.
‘A change at one point, in one molecule even, may reverberate throughout the entire system to
initiate changes in seemingly unrelated organs and tissues,’ says a recent summary of the
present status of medical research. When one is concerned with the mysterious and wonderful
functioning of the human body, cause and effect are seldom simple and easily demonstrated
relationships. They may be widely separated both in space and time. To discover the agent of
disease and death depends on a patient piecing together of many seemingly distinct and
unrelated facts developed through a vast amount of research in widely separated fields.
We are accustomed to look for the gross and immediate effect and to ignore all else. Unless this
appears promptly and in such obvious form that it cannot be ignored, we deny the existence of
hazard. Even research men suffer from the handicap of inadequate methods of detecting the
beginnings of injury. The lack of sufficiently delicate methods to detect injury before symptoms
appear is one of the great unsolved problems in medicine.
‘But,’ someone will object, ‘I have used dieldrin sprays on the lawn many times but I have never
had convulsions like the World Health Organization spraymen—so it hasn’t harmed me.’ It is
not that simple. Despite the absence of sudden and dramatic symptoms, one who handles such
materials is unquestionably storing up toxic materials in his body. Storage of the chlorinated
hydrocarbons, as we have seen, is cumulative, beginning with the smallest intake. The toxic
materials become lodged in all the fatty tissues of the body. When these reserves of fat are
drawn upon, the poison may then strike quickly. A New Zealand medical journal recently
provided an example. A man under treatment for obesity suddenly developed symptoms of
poisoning. On examination his fat was found to contain stored dieldrin, which had been
metabolised as he lost weight. The same thing could happen with loss of weight in illness.
The results of storage, on the other hand, could be even less obvious. Several years ago the
Journal of the American Medical Association warned strongly of the hazards of insecticide
storage in adipose tissue, pointing out that drugs or chemicals that are cumulative require
greater caution than those having no tendency to be stored in the tissues. The adipose tissue,
we are warned, is not merely a place for the deposition of fat (which makes up about 18 per
cent of the body weight), but has many important functions with which the stored poisons may
interfere. Furthermore, fats are very widely distributed in the organs and tissues of the whole
body, even being constituents of cell membranes. It is important to remember, therefore, that
the fat-soluble insecticides become stored in individual cells, where they are in position to
interfere with the most vital and necessary functions of oxidation and energy production. This
important aspect of the problem will be taken up in the next chapter.
One of the most significant facts about the chlorinated hydrocarbon insecticides is their effect
on the liver. Of all organs in the body the liver is most extraordinary. In its versatility and in the
indispensable nature of its functions it has no equal. It presides over so many vital activities that
even the slightest damage to it is fraught with serious consequences. Not only does it provide
bile for the digestion of fats, but because of its location and the special circulatory pathways
that converge upon it, the liver receives blood directly from the digestive tract and is deeply
involved in the metabolism of all the principal foodstuffs. It stores sugar in the form of glycogen
and releases it as glucose in carefully measured quantities to keep the blood sugar at a normal
level. It builds body proteins, including some essential elements of blood plasma concerned
with blood-clotting. It maintains cholesterol at its proper level in the blood plasma, and
inactivates the male and female hormones when they reach excessive levels. It is a storehouse
of many vitamins, some of which in turn contribute to its own proper functioning.
Without a normally functioning liver the body would be disarmed—defenceless against the
great variety of poisons that continually invade it. Some of these are normal by-products of
metabolism, which the liver swiftly and efficiently makes harmless by withdrawing their
nitrogen. But poisons that have no normal place in the body may also be detoxified. The
‘harmless’ insecticides malathion and methoxychlor are less poisonous than their relatives only
because a liver enzyme deals with them, altering their molecules in such a way that their
capacity for harm is lessened. In similar ways the liver deals with the majority of the toxic
materials to which we are exposed.
Our line of defense against invading poisons or poisons from within is now weakened and
crumbling. A liver damaged by pesticides is not only incapable of protecting us from poisons,
the whole wide range of its activities may be interfered with. Not only are the consequences
far-reaching, but because of their variety and the fact that they may not immediately appear
they may not be attributed to their true cause. In connection with the nearly universal use of
insecticides that are liver poisons, it is interesting to note the sharp rise in hepatitis that began
during the 1950s and is continuing a fluctuating climb. Cirrhosis also is said to be increasing.
While it is admittedly difficult, in dealing with human beings rather than laboratory animals, to
‘prove’ that cause A produces effect B, plain common sense suggests that the relation between
a soaring rate of liver disease and the prevalence of liver poisons in the environment is no
coincidence. Whether or not the chlorinated hydrocarbons are the primary cause, it seems
hardly sensible under the circumstances to expose ourselves to poisons that have a proven
ability to damage the liver and so presumably to make it less resistant to disease.
Both major types of insecticides, the chlorinated hydrocarbons and the organic phosphates,
directly affect the nervous system, although in somewhat different ways. This has been made
clear by an infinite number of experiments on animals and by observations on human subjects
as well. As for DDT, the first of the new organic insecticides to be widely used, its action is
primarily on the central nervous system of man; the cerebellum and the higher motor cortex
are thought to be the areas chiefly affected. Abnormal sensations as of prickling, burning, or
itching, as well as tremors or even convulsions may follow exposure to appreciable amounts,
according to a standard textbook of toxicology.
Our first knowledge of the symptoms of acute poisoning by DDT was furnished by several
British investigators, who deliberately exposed themselves in order to learn the consequences.
Two scientists at the British Royal Navy Physiological Laboratory invited absorption of DDT
through the skin by direct contact with walls covered with a water soluble paint containing 2
per cent DDT, overlaid with a thin film of oil. The direct effect on the nervous system is
apparent in their eloquent description of their symptoms: ‘The tiredness, heaviness, and aching
of limbs were very real things, and the mental state was also most distressing...[there was]
extreme irritability...great distaste for work of any sort...a feeling of mental incompetence in
tackling the simplest mental task. The joint pains were quite violent at times.’
Another British experimenter who applied DDT in acetone solution to his skin reported
heaviness and aching of limbs, muscular weakness, and ‘spasms of extreme nervous tension’.
He took a holiday and improved, but on return to work his condition deteriorated. He then
spent three weeks in bed, made miserable by constant aching in limbs, insomnia, nervous
tension, and feelings of acute anxiety. On occasion tremors shook his whole body—tremors of
the sort now made all too familiar by the sight of birds poisoned by DDT. The experimenter lost
10 weeks from his work, and at the end of a year, when his case was reported in a British
medical journal, recovery was not complete. (Despite this evidence, several American
investigators conducting an experiment with DDT on volunteer subjects dismissed the
complaint of headache and ‘pain in every bone’ as ‘obviously of psychoneurotic origin’.)
There are now many cases on record in which both the symptoms and the whole course of the
illness point to insecticides as the cause. Typically, such a victim has had a known exposure to
one of the insecticides, his symptoms have subsided under treatment which included the
exclusion of all insecticides from his environment, and most significantly have returned with
each renewed contact with the offending chemicals. This sort of evidence—and no more—
forms the basis of a vast amount of medical therapy in many other disorders. There is no
reason why it should not serve as a warning that it is no longer sensible to take the ‘calculated
risk’ of saturating our environment with pesticides. Why does not everyone handling and using
insecticides develop the same symptoms? Here the matter of individual sensitivity enters in.
There is some evidence that women are more susceptible than men, the very young more than
adults, those who lead sedentary, indoor lives more than those leading a rugged life of work or
exercise in the open. Beyond these differences are others that are no less real because they are
intangible. What makes one person allergic to dust or pollen, sensitive to a poison, or
susceptible to an infection whereas another is not is a medical mystery for which there is at
present no explanation. The problem nevertheless exists and it affects significant numbers of
the population. Some physicians estimate that a third or more of their patients show signs of
some form of sensitivity, and that the number is growing. And unfortunately, sensitivity may
suddenly develop in a person previously insensitive. In fact, some medical men believe that
intermittent exposures to chemicals may produce just such sensitivity. If this is true, it may
explain why some studies on men subjected to continuous occupational exposure find little
evidence of toxic effects. By their constant contact with the chemicals these men keep
themselves desensitized—as an allergist keeps his patients desensitized by repeated small
injections of the allergen. The whole problem of pesticide poisoning is enormously complicated
by the fact that a human being, unlike a laboratory animal living under rigidly controlled
conditions, is never exposed to one chemical alone. Between the major groups of insecticides,
and between them and other chemicals, there are interactions that have serious potentials.
Whether released into soil or water or a man’s blood, these unrelated chemicals do not remain
segregated; there are mysterious and unseen changes by which one alters the power of
another for harm. There is interaction even between the two major groups of insecticides
usually thought to be completely distinct in their action. The power of the organic phosphates,
those poisoners of the nerve-protective enzyme cholinesterase, may become greater if the
body has first been exposed to a chlorinated hydrocarbon which injures the liver. This is
because, when liver function is disturbed, the cholinesterase level drops below normal. The
added depressive effect of the organic phosphate may then be enough to precipitate acute
symptoms. And as we have seen, pairs of the organic phosphates themselves may interact in
such a way as to increase their toxicity a hundredfold. Or the organic phosphates may interact
with various drugs, or with synthetic materials, food additives—who can say what else of the
infinite number of manmade substances that now pervade our world?
The effect of a chemical of supposedly innocuous nature can be drastically changed by the
action of another; one of the best examples is a close relative of DDT called methoxychlor.
(Actually, methoxychlor may not be as free from dangerous qualities as it is generally said to be,
for recent work on experimental animals shows a direct action on the uterus and a blocking
effect on some of the powerful pituitary hormones—reminding us again that these are
chemicals with enormous biologic effect. Other work shows that methoxychlor has a potential
ability to damage the kidneys.) Because it is not stored to any great extent when given alone,
we are told that methoxychlor is a safe chemical. But this is not necessarily true. If the liver has
been damaged by another agent, methoxychlor is stored in the body at 100 times its normal
rate, and will then imitate the effects of DDT with long-lasting effects on the nervous system.
Yet the liver damage that brings this about might be so slight as to pass unnoticed. It might
have been the result of any of a number of commonplace situations—using another insecticide,
using a cleaning fluid containing carbon tetrachloride, or taking one of the so-called
tranquilizing drugs, a number (but not all) of which are chlorinated hydrocarbons and possess
power to damage the liver.
Damage to the nervous system is not confined to acute poisoning; there may also be delayed
effects from exposure. Long-lasting damage to brain or nerves has been reported for
methoxychlor and others. Dieldrin, besides its immediate consequences, can have long delayed
effects ranging from ‘loss of memory, insomnia, and nightmares to mania’. Lindane, according
to medical findings, is stored in significant amounts in the brain and functioning liver tissue and
may induce ‘profound and long lasting effects on the central nervous system’. Yet this chemical,
a form of benzene hexachloride, is much used in vaporizers, devices that pour a stream of
volatilized insecticide vapor into homes, offices, restaurants. The organic phosphates, usually
considered only in relation to their more violent manifestations in acute poisoning, also have
the power to produce lasting physical damage to nerve tissues and, according to recent
findings, to induce mental disorders. Various cases of delayed paralysis have followed use of
one or another of these insecticides. A bizarre happening in the United States during the
prohibition era about 1930 was an omen of things to come. It was caused not by an insecticide
but by a substance belonging chemically to the same group as the organic phosphate
insecticides. During that period some medicinal substances were being pressed into service as
substitutes for liquor, being exempt from the prohibition law. One of these was Jamaica ginger.
But the United States Pharmacopeia product was expensive, and bootleggers conceived the
idea of making a substitute Jamaica ginger. They succeeded so well that their spurious product
responded to the appropriate chemical tests and deceived the government chemists. To give
their false ginger the necessary tang they had introduced a chemical known as triorthocresyl
phosphate. This chemical, like parathion and its relatives, destroys the protective enzyme
cholinesterase. As a consequence of drinking the bootleggers’ product some 15,000 people
developed a permanently crippling type of paralysis of the leg muscles, a condition now called
‘ginger paralysis’. The paralysis was accompanied by destruction of the nerve sheaths and by
degeneration of the cells of the anterior horns of the spinal cord.
About two decades later various other organic phosphates came into use as insecticides, as we
have seen, and soon cases reminiscent of the ginger paralysis episode began to occur. One was
a greenhouse worker in Germany who became paralyzed several months after experiencing
mild symptoms of poisoning on a few occasions after using parathion. Then a group of three
chemical plant workers developed acute poisoning from exposure to other insecticides of this
group. They recovered under treatment, but ten days later two of them developed muscular
weakness in the legs. This persisted for 10 months in one; the other, a young woman chemist,
was more severely affected, with paralysis in both legs and some involvement of the hands and
arms. Two years later when her case was reported in a medical journal she was still unable to
walk. The insecticide responsible for these cases has been withdrawn from the market, but
some of those now in use may be capable of like harm. Malathion (beloved of gardeners) has
induced severe muscular weakness in experiments on chickens. This was attended (as in ginger
paralysis) by destruction of the sheaths of the sciatic and spinal nerves. All these consequences
of organic phosphate poisoning, if survived, may be a prelude to worse. In view of the severe
damage they inflict upon the nervous system, it was perhaps inevitable that these insecticides
would eventually be linked with mental disease. That link has recently been supplied by
investigators at the University of Melbourne and Prince Henry’s Hospital in Melbourne, who
reported on 16 cases of mental disease. All had a history of prolonged exposure to organic
phosphorus insecticides. Three were scientists checking the efficacy of sprays; 8 worked in
greenhouses; 5 were farm workers. Their symptoms ranged from impairment of memory to
schizophrenic and depressive reactions. All had normal medical histories before the chemicals
they were using boomeranged and struck them down.
Echoes of this sort of thing are to be found, as we have seen, widely scattered throughout
medical literature, sometimes involving the chlorinated hydrocarbons, sometimes the organic
phosphates. Confusion, delusions, loss of memory, mania—a heavy price to pay for the
temporary destruction of a few insects, but a price that will continue to be exacted as long as
we insist upon using chemicals that strike directly at the nervous system.
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