Question: Could you tell us about
how you got into DDT, and especially your pioneering work with
Indoor Residual Spraying, IRS.
I became interested in the DDT issue in the very early days of
my career as a medical entomologist, because DDT was, of course,
the big topic during the 1960s. I was interested in it, but by
and large I didn’t have any feelings one way or the other in
terms of DDT being bad for this or bad for that, or good for
this or good for that.
Eventually I became seriously
interested in the whole issue as I worked in the field, in
malaria control and malaria ecology. In those early years, we
were like the young lawyer chasing ambulances. We were working
in the Amazon Basin, and outbreaks were relatively uncommon,
because houses were sprayed with DDT. Anyway, whenever we would
have an outbreak, we would take off to go and investigate it.
We quickly learned that we needed to get there before the spray
teams. If we didn’t, by the time we got there, the outbreak
would be over.
Question: That fast?
That fast, instantaneous almost. I’m not saying that there would
be no cases of malaria; I’m saying that there would be no
malaria transmission taking place.
So the generation of new cases would end at that point in time.
I was impressed by the chemical - not by anything in the
literature, not by anything in the popular press, but by my
experience. So, eventually, as the opportunity presented itself,
I started conducting field experiments on how DDT actually
functions. And the outcome of the research was that I discovered
- to my total amazement, I might say - that it wasn’t
functioning by killing mosquitoes. It functioned as a repellent.
It kept them out of houses.
I actually went into the state of a recluse scientist for a
number of years, as I worked on the literature, because I
couldn’t put my findings into the context of anything that I had
been taught, or had been told. And so, I worked with the
literature for a number of years, and I discovered that there
were many like me - many field researchers - and you could find
their papers scattered throughout the literature, dating back to
the very beginning of the use of DDT. And we were all saying the
same thing: DDT was functioning in ways that aren’t appreciated.
So, one thing led to another, and I just stayed with it over the
decades.
Question: Much to the benefit of the world - especially now
with the new World Health Organization decision to use indoor
spraying of DDT for malaria control.
Well, that’s what we all hope for! It has been a very
encouraging change. And I think it was a very courageous act on
[WHO malaria head] Dr. Kochi’s part to take that position, and
to go public with it. The fight is not over, because, of course,
his decision has just rallied the anti-DDT folks, and so it’s
turning into a rather grim struggle.
But, you know, you have to decide
according to your own value system, what is the relevance of
human health versus what is the importance of speculative harms.
Question: It’s prejudice on the part of the anti-DDT folks,
really - brainwashing.
Brainwashing, exactly, and it’s everywhere. It’s in the schools.
It’s in zoos. It’s everywhere. And to a very significant extent,
it’s all false.
Question: And yet, when it’s so engrained in people - the
generations from the 70s on - it was drummed into them as a
belief system, so it’s very hard to shake it.
It’s not science. To be blunt, most people know very little
about the science of DDT, or the science about malaria control.
But they have very strong opinions - and very loud voices. And
when you see them get angry, as you mount a defense of the use
of DDT, you know that you’re dealing with a belief system, not
science.
Question: Like many environmental views that are based on
fear. ... To go back to your early work with IRS, what impressed
me was the statistics you had compiled about Ibero-America,
where you can see that the countries that stopped using DDT had
enormous increases in the rates of malaria incidence, and those
where DDT was still used, did not have malaria increases.
Right. And where the use of DDT has been initiated or restarted,
you find that malaria rates decline rather quickly,
precipitously in fact.
A baby with
advanced malaria at Garki General Hospital in Abuja, Nigeria.
Ninety percent of
malaria deaths in Africa are children under five.
Question: On the question of resistance, can you take up a
couple of the usual objections that environmentalists raise to
DDT, such as why bother to spray with DDT, because mosquitoes
have become resistant to it. Yet, what you discovered is that
the mosquitoes are repelled even if they are resistant.
I am a scientist, and the whole question about resistance and
mechanisms of resistance is really important, and those lines of
research should be pursued. But resistance to DDT - and there is
evidence in the literature to back up my belief - is largely a
product of use of DDT in agriculture.
There was a study carried out by Dr. Georghiou in Central
America back in the 1970s, and he showed that the distribution
of resistance to DDT in malaria mosquitoes corresponds precisely
with the geographical areas in which DDT was being heavily used
in agriculture.
Not only did he find that its
distribution was determined by the use of DDT in agriculture,
but he found that seasonality was influenced. In other words,
the proportion of mosquito populations and levels of resistance
within a mosquito population varies by time of year, and that
variance correlates with the time of the year that DDT is being
used in agriculture.
So the basic mechanism that I’m talking about here is that when
you put DDT on a wall, mosquitoes land on walls, and they become
exposed to DDT on the wall, because they enter a house, and they
enter a house because they want to bite a human being. The
mosquito has an option. It can not enter the house, and if it
doesn’t enter the house, it stays away from the insecticide.
If you take the DDT and spread it broadly in the environment,
the mosquito can’t avoid it. The fact that DDT is a powerful
repellent is irrelevant if it’s everywhere; it can’t be avoided.
Secondarily, DDT is a powerful contact irritant. But again, if
you can’t avoid it, it doesn’t matter that it’s an irritant. And
of course, since it’s sprayed everywhere in agriculture, it
would wind up in pools of water, where the mosquito lays its
eggs, and the selection for a resistance mechanism in those
circumstances, is powerful. And so that is the basic mechanism
of resistance selection that I’m talking about. On the other
hand, if you spray it inside houses, there are options; the
mosquito can stay out of the house, and therefore there is no
selection for resistance. But in addition, if it use of DDT has
been initiated or restarted, you find got to rebuild public
health programs, and WHO capacities to not going to be
transmitting disease.
Question: And so when you spray
the inside walls of a house, it repels all of the mosquitoes,
whether they are resistant to DDT or not.
The research that we have conducted up to this point in time
suggests to us that toxic and repellent actions are entirely
separate mechanisms of action. Toxicity is one mechanism of
action and death is a contact response. The mosquito is not
going to die unless it lands on a surface where the DDT is, and
furthermore, you really do not get significant levels of
mortality of mosquitoes unless they remain in contact with DDT
for several minutes, on the order of 20 minutes.
Question: Isn’t it part of the behavior of mosquitoes that
they rest on walls for that long?
They rest. They rest before they take a blood meal, and they
rest after they take a blood meal. That is part of their
behavior.
So, toxicity requires contact, the absorption of the chemical.
Repellency is entirely different. Repellency is a vapor phase -
no contact. The mosquitoes detect it, probably through receptors
on the antennae; that’s my best guess. They can detect molecules
of DDT in the air, and the probabilities are that they can
detect a gradient of molecules.
And once they detect that gradient
of molecules in air, they go in the opposite direction.
Question: What do you mean by gradient?
Increasing numbers of molecules in air.
Question: So, as they approach the wall, they sense they are
getting closer to the DDT and they leave.
Right. It’s the same mechanism that you would use if you smelled
smoke. Our sense of smell is acute enough that we can actually
rely on it to direct us in a particular direction if we are
smelling something. I think we’re talking about a very similar
kind of phenomenon here. The mosquito can detect a gradient of
chemical and responds, “Whoa, I’m not going there.”
Question: I think that’s been very important in the decision
by the WHO to begin the indoor spraying with DDT.
I certainly hope that it has been, because frankly, there’s no
other chemical like DDT. We know that - we’ve tested hundreds of
chemicals.
Question: What about the alternative pesticides that are
promoted, the
pyrethroids, for example, to
which mosquitoes have become resistant?
There is a growing problem of resistance to the pyrethroid
insecticides. This problem is being taken very seriously by the
World Health Organization. I know for a fact that there is great
concern about it.
The issue with the pyrethroids is
that they’re not used for public health programs alone; they are
used extensively in agriculture, and so the resistance problem
is not going to diminish; it’s going to grow. And so there is a
real need for new chemicals. There will be situations where
pyrethroids have worked well in the past, but not in the future.
At that point, what do they go to?
The environmentalists have mounted attacks on the
organophosphates, so the
organophosphates are not an optimal alternative. The
environmentalists have mounted attacks on the
carbamates, so the carbamates
are not an optimal alternative.
So what do you have other than
pyrethroids?
Question: I guess you have protection of mosquitoes at the
expense of people.
That is why we need DDT. Besides, none of these other chemicals
function as a repellent. Some are contact irritants, but none
are strong spatial repellents like DDT.
Question: The other issue people raise is, why not use
bednets, and this amazes me because of the tiny number of people
who now have bednets. I’m not against the use of bednets, but
they don’t do the job in the same way. What do you think?
I’m not particularly eager to attack the use of bednets, because
I think the bed-nets are useful and it’s not constructive to
attack them, but the problem with the bednets is the same
problem you have with any personal protective measure. It’s
fundamental, it’s basic: The problem with bednets is user
compliance. People have got to be willing, and they’ve got to
have the discipline to use the darn things every single night.
The other issue with bednets is that they provide protection
primarily when you’re beneath the net. And that’s a limitation.
People do not necessarily stay under their bednets during all
the hours when the mosquitoes are out there biting. The bednet
is an easy and popular answer to the malaria problem.
Bednets are receiving such an
enormous push right now.
So many people, and so much big
money is behind use of bed-nets. But all the hype, all the big
money, is not going to overcome those fundamental issues.
A bednet
demonstration at an Africa Malaria Day celebration in 2004.
Bednets are
useful, but alone they won’t stop malaria transmission.
As Roberts notes,
nets require “user compliance,” and they provide protection
primarily when
people are under the net, but people do not necessarily stay
under the net
during the entire time that mosquitoes bite.
There is a basic principle in
occupational health: The least desirable of all preventive
measures is the personal protective measure.
That relates to the fact that people
won’t comply. And so, the big push right now in malaria control,
the use of bednets, defies that fundamental principle of
occupational preventive medicine.
Question: Another question that’s related in my view, and
this is something that the anti-DDT people have said, is that
“We can’t do DDT, because it requires public health
infrastructure.” That boggles my mind. They are actually saying,
we don’t want to spend money on infrastructure; we don’t have
it, whereas we have the money for bed-nets. I don’t get it.
It’s putting the cart in front of the horse. You must have
infrastructure if you’re going to control the disease -
any disease. You’ve got to have people who know something about
therapeutics, about the proper treatments. You’ve got to have
people who know something about data collecting and
surveillance, making a proper determination of whether one case
is malaria and another case is some viral disease. You’ve got to
be able to distinguish between these infections.
All of that requires infrastructure.
You’ve got to know how much disease you have, how big the burden
might be, before you can evaluate whether or not your control
methods are working to control disease.
Question: I think a major problem is that there is no
infrastructure in Africa. Here we’ve taken down our public
health infrastructure too, but in Africa, it’s abysmal.
Yes, it’s abysmal, but the policies that brought about the
destruction of our malaria control programs around the world
were wrong, just flat wrong. And the people who were promoting
those changes were deluded into thinking that what we need to do
is empower the people to handle their own disease problems.
People can’t handle their own disease problems. And you can’t
empower them to do so.
Question: It seems to me that policy move was an excuse for
genocide - deaths in the millions over the past few
decades.
It has certainly been a major global reversal in public health.
No question in my mind about that. Hopefully, change is on the
way. There’s hope; perhaps that’s all we have at the moment.
Question: I have been following the news on various countries
in Africa, and they do seem to be making a fight to get back to
the use of DDT.
And if it’s not DDT, at least it’s Indoor Residual Spraying.
Because, quite frankly, I think the best of all worlds would be
a combination of spraying the walls and the use of the bednets,
ITNs [insecticide-treated nets]. We shouldn’t exclude bednets;
they should be used. But we should spray. The advantage of
spraying is that a sprayed wall is the first cut.
The mosquito has to get past that
barrier first. If it gets past that barrier, and there are nets,
maybe the nets will give the second line of defense.
Question: What do you think it would take, having been in
this field for a few decades now, to get public health back to
where it should be?
It takes a huge investment, and you can see there are signs that
the investment is growing. That’s a very hopeful change. Monies
are being made available, probably not enough, but a lot more
than we had before.
So, number one, it takes a huge investment, and number two, it
takes investment in infrastructure. We’ve got to rebuild public
health programs, and WHO capacities to direct house spraying
programs.
Additionally, we’ve got to stop
saying,
“We’re not going to do anything
unless it’s based on the community.”
We’ve got to get public health
workers back into the field doing public health for the people.
As opposed to saying,
“No, no, we want the people to
do all this.”
Question: That’s just an excuse for not doing it.
Exactly, it’s a cop-out. If you look at the history of our
efforts with dengue fever, you see a glowing example of this
whole idea of community participation. Throughout the ’70s and
’80s, the catchwords, the hype, for dengue control, was
“community participation.” It was an abysmal failure. There is
no success.
Question: In other fields that has certainly been the case,
such as community control of education. . . .
We just need to go back to what history has shown us actually
works. I have tremendous respect for the scientists of the 1940s
and ’50s, who were in there doing pioneer work in the field, on
the ground, showing how they could go about controlling disease,
and they did it. They were successful, and we have now a 30- to
40-year history of complete failure, rejecting everything that
they did.
And it’s not as if they tried and
they failed; they tried and they succeeded! And we’ve spent the
last 30 years casting criticisms on what they did, saying,
“No, we’re doing it the right
way, we’re doing it a better way,”
...and meanwhile disease is growing,
and growing, and growing.
Question: I think the words of Alexander King give a big clue
as to what happened. He said, he was for DDT during World War II
- he was a chemist in charge of DDT for Britain. And then, by
1960, when he founded the
Club of Rome with its
Malthusian outlook, he said in a memoir that he regretted his
decision to back DDT, because it had allowed such population
growth in the Third World: People weren’t dying of malaria, and
they could live and have children. I think that’s behind a lot
of the anti-DDT and other kinds of public health take-down: the
idea that we don’t need more people, and this is a good way to
get rid of them.
It certainly works!
The disease and the dying are going
on. Illness is high, deaths are high, and they just keep
increasing. Malaria is pretty good at taking people out of the
picture, so to speak.
The truth is, though, that does not solve population growth. If
you’re truly concerned about population growth, what you need to
do is focus on making those people wealthier.
Question: That is another way to look at it; people who have
a higher standard of living tend to have fewer children, so they
can raise them to have an even higher standard of living.
They tend to produce fewer children. It’s like the population
growth that we see in Japan and Europe. Many countries are very
concerned about their lack of population growth. You’ll also
find that these are rather wealthy countries.
So, I think the people who are against DDT because it prevents
disease and death, and do so from the standpoint of controlling
human population, are just terribly misled.
Question: Unless they are the Bertrand Russell types, who
advocated the use of disease as a killer.
I’ve never been able to figure out the role of that ideology
within this mix of issues. I know it’s out there. I don’t doubt
that; I just don’t know how big of an issue it is.
Question: Any time I’ve questioned persons who are opposed to
DDT, it turns out that they are Malthusians. They think that
fewer people in the world would be better. There’s no causality
there, necessarily, but those two things usually go together.
It’s the same with nuclear energy and fusion. . . . They oppose
it because it will lead to cheap energy and more
industrialization.
It’s very sick, and it’s wrong - it’s wrong ethics and wrong
thinking.
Question: Can you talk a little about the book you are
writing?
This book is about DDT. It is written to build a solid
foundation of science for dealing with the questions about DDT.
In the book, we try to explain how DDT actually functions to
control disease transmission, and how it is, in fact, unique in
the way that it functions. We explain that DDT is not a very
toxic chemical, and try to put its persistence into perspective,
in terms of compartmentalization, sequestration, and
biodegradation.
There are lots of misunderstandings about DDT. There is a strong
belief that DDT does not biodegrade; it does. It’s readily
biodegraded. It’s biodegraded in the human body. It’s
biodegraded in the bodies of most living organisms. It’s
biodegraded by bacteria. It’s biodegraded by fungi. White rot
fungi can mineralize DDT. So it is ubiquitously degraded in the
environment.
It is also degraded by light. It’s chemically degraded. And so,
when you start looking at all the mechanisms for breaking down
DDT, what you really discover is that DDT is persistent, only to
the extent that it is protected from all of these processes, by
becoming tightly bound to organic particles in the soil, for
example. In the process of compartmentalization, it becomes
stored in fat. Basically DDT in a fat cell is not available for
degradation. In addition, when it’s in fat, DDT is not available
to act against the living organism.
So, this whole concept that DDT is persistent, and that this
persistence is a problem, is wrong. The fact is, the natural
world is fully capable of dealing with DDT, because we are
surrounded by chemicals like DDT.
Degradation, sequestration, and
compartmentalization are natural processes for dealing with DDT
and other DDT-like chemicals. There are certain vitamins that
are toxic, but they are essential to our survival. Some
lipophilic chemicals will bio-accumulate, and the way nature
handles such a chemical is to tuck it away in fat.
Basically that’s the process of compartmentalization. If you
were to take the process of sequestration and
compartmentalization of DDT away, DDT would be degraded and
disappear.
Question: It seems to me, from looking at experiments
reported in the DDT literature going back to the 1960s, that DDT
in the animals it was given to, had a kind of protective effect.
In other words, the dogs who were given very high doses of DDT,
did a lot better than the control group. They got sick less and
they lived longer. Did you deal with this at all?
Well, let me give you one example. I don’t know that I can say
anything profound about it. By and large, within a living
organism, DDT becomes a neutral factor. It’s neither good, nor
bad; it’s just there. And because it’s tucked away in fat, it’s
biologically inert.
But there are systems for moving DDT
out of fat, and getting rid of it, just as there are systems for
moving any other lipophilic toxins out of fat and getting rid of
them.
So none of this is new to nature.
We are literally surrounded and
immersed in an environment of lipophilic chemicals. Some are
toxic, some are less so, and we deal with all of them. Some of
them are essential to our survival. DDT is not essential to our
survival, but there are certainly mechanisms for dealing with it
in a natural way.
The example I was going to give you: You’re familiar with the
robin story, which Rachel Carson described. She stated that the
robin was headed for extinction because of DDT. Well, a study of
many aspects of the robin story was published in 2000, and
another in 2003. DDT was used heavily in apple orchards. In
fact, there was probably more DDT placed on apple orchards than
any other commercial crop.
And so, there are these orchards in
Canada where DDT had been used until 1973. There was still a lot
of DDT in the soil. If you test the robins that live in that
orchard, they have higher levels of DDT than any other bird
recorded. And you find high levels of DDT in the earthworms.
But if you compare the populations and reproductive success of
robins in the orchard, with the robins in surrounding areas that
have no DDT, you find that the robins are doing just as well,
with the DDT, and in fact, the brood and clutch size of the
robins in the orchard are actually higher than the brood and
clutch size of robins in areas without DDT. The difference is
not statistically significant, but they are higher.
So basically, what you find is that the DDT is there, but it
causes no harm, and certainly does not affect reproduction.
Question: I think that the robin story promoted by Rachel
Carson is a complete lie, because there were plenty of robins in
1962 when she wrote her book, and later.
It was a complete lie. What she focused on was what happened on
a Michigan State University campus in Ann Arbor, and so she made
all those wild claims. There were studies done and published in
1973 by ornithologists on campus, and what they showed was that
Carson’s data were all wrong. They saw that there were just as
many robins during the time that DDT was in use as before or
after DDT use.
And in fact the nesting populations
of robins were higher during the DDT years than before or after.
But the anti-DDT people don’t want to know that...
Question: Can you say a little more about your book?
The goal of the book is to try to set the record straight on
DDT. And, more important, to show how the use or nonuse of DDT
was a critical public health issue that had implications for the
health of hundreds of millions of human beings. Hundreds of
millions of people have been harmed by the
environmentalist-activist campaign against DDT.
The outcome of the enormous propaganda machine has been to give
over to the environmental organizations, like
EPA [U.S. Environmental
Protection Agency],
UNEP [United Nations
Environment Program], and many others around the world,
authority, regulatory control over a critical public health
issue, and they have no recognition of the public health
consequences. They have authority; they assume no
responsibility.
That’s one of the points that we try to explain in the book -
that the reason that people have been harmed is that the
authority is resting in the wrong hands.
Question: And people are continuing to be harmed until we
change that situation.
It should change. If there is any justice in the world, the
authority over the public health insecticides will be taken away
from the environmentalist organizations, and will be put in the
hands of the people who have responsibility for public health -
WHO, or CDC [Centers for Disease Control].
There should be change; whether or
not there will be change is an open question.
Question: It’s a fight! When does your book come out?
I’m working on the eagle story right now and to be fair, and to
get the science right, is very difficult. I’m spending a
tremendous amount of time researching, as are my co-authors. I
know more about eagles than I ever wanted to know. This is the
last chapter I’m writing, and I hope to have it finished in the
next two to three weeks.
Question: One last question: For years the environmentalists
have been trying to come up with reasons that DDT is “bad” -
whether it’s shrinking crocodile penises or hurting the
development of Mexican-American children (the recent California
study).1 They are just trying to find something, but to my
knowledge, they have never found anything in DDT harmful to
human health. Can you comment on the University of California
study on DDT and infant development?
I think the California study falls into the same category as
many of these studies.
Basically it comes down to the
existence of large data sets, and the numbers of large data sets
are growing. We are dealing with statistical manipulations,
looking for correlations with a large number of variables, and
you set your probability for statistical significance at 5
percent, and well, one out of twenty columns of data is going to
give you a significant result; that’s 5 percent. And I think
that’s what is happening.
There is some weak association, and
with a large data set, it may give them a statistically
significant finding, and they go with it.
Somebody else comes along, and has a different large data set,
and they find that, no, it just doesn’t work out that way. Those
are the problems that we are dealing with: One study finds an
association and another study doesn’t. It is a search for
something harmful from a chemical that we can detect in
extremely small quantities. And it’s often there, so it’s a good
target.
Occasionally somebody gets a hit, and they go to press with it.
Through this process, we also run into the bias against negative
results. If you do a study that duplicates the Eskenazi study
[the University of California study of Mexican-American
infants], and you find no association, your chances of getting
that paper published are extremely small, because it’s a
negative result.
That’s a bias in the whole process
of publishing scientific studies, and it’s real. There’s no
figment of imagination here. If you’ve got a negative result,
that result is just not very helpful.
If we had 10 studies, and they all showed the same thing about
developmental effects, you might reach the point that you can
say, there’s something real in this association. I’m talking
about well-designed, well-performed scientific studies all
showing the same result. Then you might say, well, let’s look at
it. Now, just because studies show a developmental effect, does
that mean DDT is not good? In my opinion, it doesn’t mean that
at all. What you have to do is take a look at what is harm
versus benefit.
If you’ve got a population where you’re losing 100,000 babies to
malaria a year out of a population of 20 million or so, boy,
you’d better have some serious, serious harm coming from the use
of that chemical if using it will save 100,000 lives.
Question: What the study showed was so inconclusive, that at
a certain point of the infant’s development, the child was one
or two months behind. That’s meaningless, really.
It’s particularly meaningless when you realize that it’s very
possible that even if there were an effect, it could disappear
over the next two or three years of development.
Question: And how many other things are so much more
important in terms of a child’s development?
The true significance of that paper was not the science, in my
opinion, but that the authors stepped over the line, and made
the suggestion that the results of their study should be taken
into consideration by those countries looking to use DDT for
malaria control. In my opinion, the authors were over the line
because they knew nothing about malaria or the benefits of DDT.
For them to cross the line and say
that those countries should look at their study results before
making a decision to use DDT is, I think, unacceptable -
scientifically and ethically unacceptable.
Question: It’s also unacceptable that it was picked up and
ballyhooed everywhere, including in the science press with the
same intent.
Donald
R. Roberts, Ph.D., an entomologist, is Professor of
Tropical Public Health at the Uniformed Services
University of the Health Sciences in Bethesda, Maryland.