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1961. The practice
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for five agricultural crop pests. In E. J. LeRoux
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Canadian Entomol. (in press).
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Ecological Considerations in Chemical Control
Implications
By
ROBERT
to Man
J. ANDERSON
Assistant Sttrgeon General and Chief
Bureau of State Services, U.S. P. H. S., D. of H. E. W., Washington, D. C.
In recent years, the use of chemicals to control pests
has increased rapidly, with a corresponding increase in
both benefits and hazards to mankind. In the early years
of their use, pesticides were considered almost solely in
terms of their contributions to our comfort, safety, and
productivity.
Now, general attention is focused on the
possible harmful effects which have to be avoided, or
controlled, in the widespread application of the powerful
new chemicals.
on man. The fact that these insecticides are poisons, at
least potentially dangerous to human beings and to wildlife, was and is a cause for serious concern. It is this
potential that demands that a research and surveillance
program for these insecticides extend into the time of
their field use.
Our studies on DDT, as well as on some of the newer
chemical compounds, have continued up to the present.
We have been able to fit together only part of the picture, l:owever, of what the consequences of pesticides
use may be to mankind. There are some gaps where
important pieces are missing and we are exploring, more
thoroughly than ever before, the cost we may be paying
for these benefits of pesticides.
Up to 1940, the pollutional effects of pesticides were
not thought of as a problem. The early insecticides consisted of the arsenicals or natural occurring organicssuch as rotenone and the pyrethrins-which
were tightly
bound to the soil or which decomposed rapidly upon
application. Also, these materials were not used in any
appreciable quantity.
Investigations have shown us that pesticides have not
always been used as recommended by the manufacturers
and by various governmental agencies, and that this has,
on occasion, resulted in the poisoning of human beings
and the destruction of wildlife. We know that poisoning
of human beings has been caused by at least 49 different
pesticidal chemicals, with diverse and complex clinical
effects.
After 1940, the chlorinated hydrocarbons,
many of
which are stable and resistant to biological decomposition, and the organic phosphorus insecticides, with their
high toxicity effects, were developed and usage began to
increase rapidly.
In the brief span of little more than 20 years, a new
kind of environment has been created. In this short
period, at least half a million new chemical compounds
have come into existence.
of
Evidence has also accumulated which suggests that
effects of certain pesticides may contribute to, or enhance, certain pathological conditions or diseases affecting the muscles, nerves, the central nervous system, and
possibly the bone marrow and liver of human beings.
For example, they have been indispensable to enlarging food and fiber production. They have been importantly employed in the control of diseases carried by
insects and other vectors.
They have proved to be
among the most effective weapons which medical science has ever had available for the control of certain
diseases. Malaria and murine typhus fever, for example,
once two of the most deadly scourges of mankind, have,
with the use of insecticides, been virtually eradicated in
the United States.
Also. our concern has been increased by the discovery
of pesticide residues in the bodies of people and animals
and in many components of the environment. Since the
majority of pesticides have been little studied for their
full effect on man, there is no way to exclude the possibility-for
even the better-known pesticides-that
subtle
dangers still remain to be discovered. The presence of
any foreign chemical in the general food or water supply
is not a matter to be dismissed lightly, even though,
with minor exceptions, the safety record of pesticide
usage in North America and Europe appears to be good.
When the Public Health Service began to use DDT
in its disease-control programs in the 1940's, our scientists began to study also its possible harmful effects
For example, the death rate from poisoning by pesticides in the United States is 0.09 per 100,000 population,
and no known cases of illness in the United States or
These chemicals have given us vast new powers
manipulating and controlling our environment.
74
sentatives of each of
terior; Agriculture;
and Wel£are-began
of 1961 and by now
meetings.
the United Kingdom have resulted from insecticide residues on food when formulations have been used according to directions. But we must remind ourselves that
these statements
relate to the immediately apparent
effects of pesticide exposure. Since we know relatively
little about the precise fate of any of the pesticides in
plants, in the soil, or in man, it is impossible definitely
to evaluate the role which pesticides play in the production or support of certain human diseases.
the four member Departments-InDefense; and Health, Education
holding Board sessions in the fall
have held just short of 40 regular
The Board set out to examine all Federal programs in
which substantial amounts of pesticides are used. Each
such program was described, in writing, by the agency
proposing it in terms of its location; obj ectives; j ustification; chemicals to be used; characters and size of the
acreages to be treated; details of the chemical applications-including
methods of application, timing, number of applications, and dosage; special precautions to
be exercised; other Federal Departments, State and local
governmental agencies, and private interests involved;
and possible adverse effects. These descriptions were
submitted to appropriate experts of each member Department for analysis and comment. The descriptions,
comments, and questions then formed the basis for discussion in Board meetings which could lead to clearance,
or a request for revision, of the proposed program.
In recognition of general concern over contamination
of the environment with pestieides, the President's Science Advisory Committee report on the "Use of Pesticides," which was issued May 15, 1963, contained numerous recommendations, including a mandate that various government agencies take action to increase our
knowledge of pesticides and develop procedures to ensure their safe use.
Those of us who have been close to the pesticides
problem for some years welcome this upsurge of interest
in the state of the environment, and are ready to push
our research efforts into the areas which have remained
relatively unexplored.
Experience on the Federal Pest Control Review Board
has convinced me that the discriminating use of pesticides and protecting ourselves from ill effects rests
squarely on the availability of reliable data about the
pest problem and its consequence and, on the other hand,
about pesticides and the consequences of their use.
The Committee report pointed out that approximately
$20 million of Federal funds were allocated to pest
eontrol programs in 1962, but that no funds were provided for coneurrent field studies of effects on the environment.
It is the situation symbolized by these
statistics that we need to correct.
'vVe have encountered instances of inadequate information in attempting to make decisions at Board meetings,
and it is a certainty that we will encounter this problem
again. Meanwhile, we attempt to provide an additional
safety factor and serve as an overseer of Federal programs, in order to achieve essential goals with utmost
protection of the public interest. We serve as a goad to
public agencies and to private operators, alike, in making
both more alert to the side effects of specific pesticide
uses.
\Ve have very little information about pesticides and
man's ecology, compared with the totality of what we
need to know. We have some data on the acute and
immediate effects of pesticides on people, plants, and
animals. We have spotty knowledge about the amount
of pesticides in air, water, soil, and food found in sporadic sampling programs, but very little in the way of
integrated conclusions about the composition of our
environment in various parts of the country and the immediate and long-range ecologic effects, including those
on human beings.
However, one benefit to all of us-users,
overseers, or
students of pesticides-would
be an increase in research
to the point where we might have at hand an organized
body of facts upon which to base sound decisions. This
need for more information is urgent.
'We face many questions we cannot answer fully and
precisely.
For example: Is it the residues in food that constitute
the important exposure for most people?
Or is it
people's own use of pesticides around their homes, lawns,
and gardens that poses a hazard? What are the effects
on a neighborhood and its residents of drift, run-off, and
other factors which may transport a pesticide far from
its original site of application?
I visualize our next big stelr-in determining the ecological implications to man of the new chemicals-as
a
series of comprehensive and very detailed studies of the
environment in selected geographical areas of our country.
The Public Health Service is now planning to initiate
pilot area studies, in which the types and amounts of
pesticides used, and the amounts of pesticides present in
air, water, diet, clothing, lawns, and houses will be
measured in a selected group of communities.
These
studies will trace the movement of pesticides through
the environment, whether through air, water, food, or
soil. Studies will be made to determine the ways in
which pesticides in the environment find their way into
people's bodies and the amount of residues that remains
there.
I n the absence of better answers to these and other
questions than we have now we work nearly blindfold in
formulating solutions or policies governing pesticides use.
Federal agencies and many other groups are-and
have
been for a long time-cognizant
of the need to use, in
the safest way possible, the smallest amount of the properly chosen insecticides that is effective, and that only
when nonchemical methods of control have been exhausted.
To help ensure sound, effective operational programs
in the use of pesticides by Federal agencies, the Federal
Pest Control Review Board was established in mid-1961,
and requested to give particular attention to preventing
adverse effects from pesticides, on human health or on
valuable forms of plant and animal life. Two repre-
\Ve will select communities which will be representative of the various geographic areas of major pesticides
llse, taking into account variations in the following factors: type of pesticide in predominant use, methods of
application, and pathways of e..xposure to man.
7S
Any of us who have experience in this field of study
do not expect the efficient control of pests or even research on control methods to be a simple matter. You,
perhaps more than any other group, are aware that in
order to selectively kill a pest species, one must know
a great deal about its physiological perculiarities and be
acquainted not only with its biology but the biology of
other species, including human beings, that live with it.
This requires a knowledge of comparative physiology
and ecology beyond our present achievement.
sponsored programs from research on broad-spectrum
chemicals to more support for research on (1) selectively
toxic chemicals;
(2) non-persistent
chemicals;
(3)
selectiye methods of application; and (4) non chemical
control methods, such as the use of attractants and the
prevention of reproduction.
Certainly an exciting aspect of the scientific quest
which involves entomology is the attempt to manipulate
normal or genetic processes in such a way as to cause
the pe;t species to expend its own energy in destroying
itself and, in so doing, provide suitable alternatives to
chemical controls.
Because of species variation, data obtained from animal experiments and observation can be utilized only to
give general guide lines for human reactions. This fact
provides one of the urgent reasons for studying human
reactions and the composition of the environment in
typical U. S. communities.
Meanwhile, I find very appealing the argument that
what is needed in determining standards for use of
pesticides is not blanket prohibitions
against broad
classes of pesticides, but rather a pinpointing of the uses
which give rise to adverse effects, and, based on this
knowledge, modifications which are required to overcome
the adversities.
Just as registration of a pesticide for
marketing is based on merits of specific use, so should
restrictions be arrived at by specific study.
Because of the introduction into our environment of so
many new compounds, and because of the increasing
total use of chemicals, it is extremely important not only
to examine the levels of tolerance for individual pesticides but to determine, also, whether danger occurs when
there is exposure to two or more compounds below their
respective toxicity levels. The effect of a pesticide may
he quite different when combined with another chemical
than when it is a unique stimulus.
To assess the long-range and short-range effects of a
given pesticide in man one must have certain basic information, which would include:
1) The extent of its usage, and the methods of application
2) Its acute and chronic toxicity
3) The amounts of the pesticide that appear in water,
bod, animal foods, etc., under conditions of actual
usage, and the amounts which will reach human
beings directly and indirectly
4) The probable chemical transformation
that the
chemical will undergo in storage, and as a residue
5) The amounts and identities of these transformation
products that reach the human consumer
6) The acute and chronic toxicity of each of these
transformation
products.
As you know, many variables are involved in the use
of chemicals. It is necessary to be familiar not only with
the physiology of the target but with all the details concerning the methods of application of the pesticide being
used in weighing the effects of an application. For example, persistence or degradability of a pesticide, a subject of great interest right now, is a function of nearly
a dozen different characteristics,
such as nature of the
plant surface, formulation
used, plant growth, rain,
humidity, volatilization,
wind, temperature,
light, and
inherent characteristics of the pesticide.
Regarding persistence, the President's Science Advisory Committee recommended that "accretion of residues
in the environment be controlled by orderly reduction in
the use of persistent pesticides."
For example, we know that organic phosphate insecticides have a combining effect with proteins.
In this
respect, one needs to know whether they do indeed, combine with cellular constituents, such as DNA (deoxyribonucleic acid), and whether, from such combinations,
cellular alterations result. Such cellular alteration as
is now generally recognized results in mutogenesis (genetic changes) or carcinogenesis (cellular proliferation)
which constitutes cancer.
What is the meaning of this recommendation if we
translate it into a program of action by a Federal agency
such as the Public Health Service or the Pest Control
Division of the Department of Agriculture?
The chlorinated hydrocarbons
are persistent in the
environment. The organic phosphate compounds, on the
other hand, are rapidly degradable and nonpersistent. Do
we then eliminate the use of the chlorinated hydrocarbons
and substitute in their place the organic phosphate compounds? To do so might lead to some very undesirable
consequences. The so-called persistent chemicals have,
in general, a fairly low toxicity for man, while the organic phosphate compounds are characterized
by high
toxicity, even though they are rapidly degradable, nonpersistent in the soil, and quickly metabolized and excreted from the human body.
To ascertain such properties and effects, we shall have
to supplement our community studies by other research.
'vVe are, for example, planning to expand our detailed
studies of various specific occupational groups which
have prolonged and intensive exposures to pesticides. \Ve
have a responsibility to make sure that the workers in
manufacturing,
transporting, loading or applying chemicals are safe from any effects harmful to their health.
Also, it seems apparent that the persons working
under conditions of maximum exposure should yield the
first clues of hidden hazard. Our proposed occupational
surveys will encompass medical findings, clinical examination of workers, determination of conditions of exposure, biochemical studies of pesticide metabolites, and
early derangement in body metabolism.
'vVe hope to
determine the gross effects of pesticides on the organs,
tissues, blood, or cells of human beings, in terms of both
acute and long-term, low-level exposures.
If we were to plan seriously to use either less persistent or more specific compounds than those we now
have available, we might find ourselves introducing into
the environment in greater amounts than we do now a
larger variety of chemicals more toxic to man.
The President's
Science Advisory Committee suggested, as one approach in developing safer, more specific control of pests, a shift of emphasis in Government76
In addition, we are planning new approaches to toxicological studies of animals other than man. In research
with experimental animals, the biological action of pesticides will be studied with reference to routes of intake
(inhalation, absorption through the skin, or ingestion);
the specific site of action or organ affected; and the
metabolic fate of the pesticide in the body. These bioassay procedures should provide more information on
.specific effects of pesticides on the cells, the central
component of the cell (DNA), the tissues, and the blood
enzymes. These effects will be correlated
with the
amount of pesticide exposure.
These studies will extend beyond the conventional or
classical toxicity studies undertaken in current programs
of Public Health Service laboratories, or elsewhere, and
will complement their efforts in determining whether
particular
pesticides are persistent in the soil, plant
growth, and in the bodies of animals and man; whether
particular
pesticides have harmful effects in altering
chromosomes
(cellular DNA)
which produce genetic
changes; whether particular pesticides act on cells to
cause cell proliferation
which constitutes cancer; or
whether pesticides, combining with other agents-other
pesticides, drugs cosmetics, paints, or whatever it may
be-have a harmful effect in the combination.
For all these efforts, there must be available highly
sensitive and rapid analytical procedures for measuring
minimal or trace levels of pesticides in the environment
(air, water, milk, food, total diet, soil and the like)
and body tissue and so increased efforts may be directed
to the development of better analytical methods.
Many of the contaminants increasingly present in our
environment are present in almost immeasurably small
quantitites. A recent report of our Public Health Service Water Quality Network, for example, tells about evidences of DDT and dieldrin in 38 samples of water
taken from 10 rivers during the period from May
through December 1962. The samples were identified by
examination of the infrared spectra of carbon adsorption
extracts.
Although these concentrations are described as "well
below those known to be toxic to fish or presumed to
be hazardous to man," those of us who are concerned
with control of pollutants in man's environment know
that only by applying extraordinary
measures can we
get these substances out of water, once they have
entered it.
icals, it is to our interest-and
it is our responsibility-to
support improved programs of research and surveillance,
and to help point the direction which we think these
programs should take.
The long-term implications of exposure to environmental factors are difficult to investigate. Some of the
research relevant to determining the ecological impact
of pesticides will require continuous, generous financial
support, extensive facilities for broad approaches from
fundamental points of view, and great devotion and commitment by scientists who go into this type of work.
The problem of chemical mutagenesis and carcinogenesis, as well as the totality of environmental influences and interactions on health, are so vast that it is
important to develop programs, ideas, and findings on
a long-range basis and on an international scale. As an
example of the new approach, I call your attention to
the proposal which the \\Todd Health Organization has
made to set up an institute to study, on an international
basis, the production of mutagenesis and carcinogenesis
produced by chemicals.
The National Geographic Society in October 1963
reported that biologists of 30 to 60 nations are e.'Cpected
to participate in a study, under the auspices of the International Council of Scientific Unions, to coordinate
international research (1) on food production and (2)
on man's ability to adapt to different environments.
There are other international studies, in progress or
under consideration, which will augment our store of
information.
I believe we may be on the threshold of tremendous
new discoveries which will help us to understand the
ecological implications to man of the new environment
he has created for himself and to act on these implications.
I am delighted to have the opportunity to discuss these
matters with you because you are the people who are
constantly seeking better methods of pest control, and I
consider this activity vital. Those of us dependent on
chemical pesticides look to you entomologists with great
hope that you can develop alternative,
nonchemical
control methods.
Our ultimate, mutual objective is long-term pest population management by methods which, while achieving
their obj ectives, offer no serious hazards to man or to
his environment. There is promise, in the almost miraculous gains of the past two decades and in the research
proposed for the future, that we shall achieve this goal.
'vVe find ourselves in a situation which is becoming
more and more familiar in this technological age. There
are many benefits of modern life which bring with them
recognizable risks, and we are required to bring about
the most favorable balance possible between these extremes.
With every effort to eliminate a pest hazard, all of us
are confronted with the need to examine not just the
effect on the target pest but the ecological implications
to mankind of the control which is used. This process
of examination relies heavily on your work as entomologists and on our work in public health.
At present, pesticides constitute one of the factors in
man's ecology which pose benefit and risk. Our purpose
must be to be fully aware of the risks and to reduce
them; to balance the benefits and the hazards, recognizing that there may be certan risks not worth taking.
Our tasks, as entomologists
and as public health
workers, so far as they involve pesticides, are closely
allied and must be pursued almost concurrently.
Our
interdependence, in determining the ecological implications to man of his own use of chemicals, is necessary
and inevitable. For this reason I value very much the
chance to meet and talk with you today about these
matters which are of great importance to all of us.
I am suggesting, urgently, that research and surveillance be greatly accelerated now, in view of the increased
pace of development of chemical controls in the past two
decades. Since all of us can benefit from the expansion
of research programs and the scientific study of chem-
77