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About the Author

Bart Knols
Medical Entomologist (Dodewaard, Netherlands)

Bart G.J. Knols (1965) is the Managing Director of MalariaWorld, the world's first scientific and social network for malaria professionals. He is a malariologist with a Masters degree in Biology and a PhD in Medical Entomology from Wageningen University, the Netherlands. He also obtained an MBA degree from the Open University (UK) in 2006, for which he won the prestigious international ‘MBA Student of the Year 2007 Award’ as well as the Alumnus of the Year Award from the Open University. With 11 years of working experience in Africa he has managed large-scale research and vector control programmes on malaria for ministries, international or national research institutions. He has worked for the UN (IAEA) as a programme manager for three years, has served as a consultant for the World Health Organization, and is currently a Board Member of the UBS Optimus Foundation, the second largest charity in Switzerland. He has published over 130 peer-reviewed research articles, has written 16 book chapters, and has served as senior editor on a WHO/IAEA sponsored book on implementation research. In 2007 he co-edited a best-selling book titled 'Emerging Pests and Vector-Borne Diseases in Europe'. He received an Ig Nobel Prize (2006), an IAEA Special Service Award (2006), and in 2007 he became a laureate of the Eijkman medal (the highest award in the field of tropical medicine in the Netherlands). He has been a member of the Royal Dutch Academy of Arts and Sciences since 2004. Bart held an Assistant Professorship at Wageningen University until April '09 with projects across Africa. He currently directs K&S Consulting, a firm he founded in the beginning of 2007.


DDT: Sniffing Out Excellent White Powder

Published 22nd June 2010 - 109 comments - 38618 views -

No, no, it’s not that white stuff. It’s that other white powder. The one that makes some of us go mad with anger, whilst others relentlessly defend its use. That some claim will give you breast cancer, whilst others say you can drink and inhale it without any harm. That some claim will destroy our environment, whilst others oppose by saying it will save millions of lives.

Here’s the story of DDT: Mankind’s most controversial chemical ever. Discovered in 1874 by a chemistry student named Otmar Zeidler. Found to be a superb bug killing chemical inddt the late 1930s by Swiss chemist Paul Muller. For which he got a Nobel Prize in 1948.

If you read this and live in the Southern USA, Europe, Russia, Australia, Taiwan, or the Carribean, say ‘Thank You’. Millions of houses in these parts of the world were sprayed with DDT between 1940-1960, resulting in the disappearance of malaria. Because of DDT, when you go to sleep tonight you don’t need to worry about malaria anymore.

But hold on. Didn’t we hear about DDT in school as the chemical that led to the (almost) extinction of the American bald eagle? The US national symbol with its white-feathered head? Because of thinning egg shells and loss of reproductive capacity? Yes we did. And weren’t we told that DDT was accumulating in the food chain and causing endless harm to the environment? Yes we were. And was it not thanks to biologist Rachel Carson that published the book Silent Spring in 1962, that the world opened its eyes making the stuff banned in the early 1970s? Indeed. So?

Listen to Carson first…

Lies, scare mongering, and environmentalist lobbying

According to Prof. Don Roberts and co-authors, who recently published the book ‘The Excellent Powder: DDT’s political and scientific history’, we were all fooled by a bunch of liars, including Carson. Roberts goes as far as accusing the greens for deliberately forcing the ban on DDT so that developing countries could not be protected from malaria and thus avoid an unbridled population explosion. Saving Africans from malaria would merely result in a population explosion. Better get rid of DDT.

Roberts uses 432 pages to tell us that the greens lied to us about the fate of the Bald Eagle, the peregrine falcon and robins during the period that DDT was used widely in US agriculture. He blames hunting and habitat loss instead of DDT and uses page after page to show us he is right. Every claim by the greens is met by an anti-claim of Roberts. Why does he do this?

DDT was responsible for freeing a major part of the planet from malaria. It is cheap, very effective, and saves lives because it kills mosquitoes. Roberts wants more widespread use of the stuff in Africa (beyond the 4-5 million kg sprayed there already each year). He argues that not a single person has ever suffered any health effects of DDT, that it biodegrades eventually, and that humans merely store it in the fat tissues and eventually get rid of it.

A report prepared by fifteen US/South African scientists, the Pine River Statement, condemned DDT and held on to what they consider studies that unequivocally demonstrated human health effects of DDT, still officially declared as a carcinogen. Roberts puts the (almost 500!) studies on which the report was based away as ‘un-replicated, contradictory, or statistically insignificant’. Roberts takes on a British Journal of Urology article by accusing them of ‘manipulating data’. Finally, his resentment of one of the foremost scientific journals Science is apparent by accusing them of being biased and guilty of fraud. Heavy statements.

excellent powderBut doesn’t DDT lead to resistance in mosquitoes? Yes it does. But Roberts uses endless studies to defend his point that resistance doesn’t matter. DDT is keeping mosquitoes from entering houses. Fewer bites, less malaria. That mosquitoes are becoming resistant to the stuff is not important, an issue for which Roberts goes head-on with the World Health Organisation. And if this isn’t enough he also accuses them of being weak and subjected to political agendas and falling for the nonsense coming out of environmentalists.

It remains to be seen if Roberts’ book will open the eyes of environmentalists and the broader public. Politicians will be careful to stay away from DDT – it is much too controversial. Scientists seeking new solutions to control malaria will continue to use DDT as the example of how things should not be done. The pesticide lobby producing what they consider more benign chemicals for mosquito control will support a permanent ban of DDT.

The net result: The disease that no longer bears on us is killing a million kids in Africa each year. And that’s our fault, thanks to the greenies, says Roberts.

Roberts and co-authors stand out from the crowd. But what if they are right?


Roberts, D., Tren, R., Bate, R. and Zambone, J. (2010). The excellent powder:  DDT's political and scientific history. Dog Ear Publishing, USA. 432 pp. More about this book here.

Category: Health | Tags: africa, africa, malaria, environmentalism,


  • Christophe BOETE on 24th June 2010:

    Thanks for this interesting point Bart!

    Just to add an information to your post, both Tren and Roberts are part of Africa Fighting Malaria which is an NGO in favour of the use of DDT… and this echoes a paper published in Le Monde Diplomatique a couple of years ago ‘Revenge of the DDT’ (in french: in portuguese:,a1349) mentioning the link between this NGO and a couple of companies (including Exxonmobil)
    It would certainly be interesting to know if any of those are producing DDT and how these relations affect (or not) the position of AFM on the use of DDT…

  • Bart Knols on 24th June 2010:

    @Christoph. Thanks for bringing up these articles. The comment that ‘The ban of DDT caused more deaths than those caused by Hitler’ is particularly striking.

    As far as I know, DDT is only being produced in India and China at the moment, and due to be phased out completely by 2017. Roberts and Tren fight to stop this complete ban, but the odds are against them I’m afraid.

    However, when I read the book, it really did make me think twice about DDT, I must confess. Roberts certainly makes a compelling case.

    And, with more than 600 views of this blog, and only 1 comment so far (from you) indicates that this is a very sensitive issue that people don’t want to get involved in…

    So thanks for opening the debate, I look forward to seeing more contibutions.

  • Christophe BOETE on 24th June 2010:


    Another comment…

    I tend the find the sentence ‘The ban of DDT caused more deaths than those caused by Hitler’ a bit dubious.

    How many malaria deaths are due to socio-economic hardship generated by the public health reforms (SAPs) in Sub-Saharan Africa or in Central and South America?

    What would it cost to favour the development and use of efficient and environmentally friendly methods?

  • Bart Knols on 24th June 2010:

    @Christoph. That is indeed a dubious statement, but powerful nevertheless.

    The fight of Roberts and colleagues to get DDT more widely used again in malaria control does have a negative effect: the search for truly environmentally benign alternatives. This is what I eluded in in my blog that science may cripple development:

    In their book they do admit that robins were killed immediately after DDT spraying, they do agree that egg shells thinned (but did not make bald eagles extinct), and they do admit that DDE accumulates in the food chain. But they argue that that is not harmful…

    Suppose that this is true. Then still the argument holds that we may not wish to have such chemicals lingering around in nature (at times for a very long time). It gets back to the ‘precautionary principle’, as there may be effects that we don’t know of yet but manifest themselves only after prolonged exposure.

    In the book they argue that chemicals that are very closely related to DDT are present in the environment. I find that a weak argument - chemical A may be deadly, chemical B (with a minute structural difference) may be completely harmless.

    They argue that because DDT is an organochlorine that other compounds with chlorines are accepted by us, and they use table salt (sodium chloride). Also this is a weak argument, as if all chlorinated hydrocarbons are the same…

    Finally, and this argument will upset many, they claim that because of malaria, African families compensate for children lost to malaria by producing more. They than crawl under the skin of an African person saying ‘They may think “we must do something about this disease before we lose more of our children”. This is a pretty far-reaching conclusion (particulalry in view of the availability of bednets).

    There are more issues raised in the book that are debatable, let’s see if others want to chip in here first…

  • Tullu Bukhari on 24th June 2010:

    Hi Bart,

    Thank you for bringing up this topic. It is good of Roberts and co authors to research and compile the facts and issues related to DDT’s ban.

    I will comment on the paragraph related to the development of resistance against DDT and the role of environmentalists.

    Like you said, resistance will develop against DDT but it also developed against pyrethroids soon after their introduction over 30 years ago. The resistance against pyrethroids, has been proved possible to manage in many field situations. Same would have been the case for DDT.

    As far as the environmentalists are concerned, the Golf of Mexican oil spill is the latest example, where the highly sophisticated, robust and perfect reasoning, from them, led to off-shore drilling (a big mistake) which in turn caused a highly sophisticated, robust and perfect disaster. Banning DDT was a similar big mistake…..

  • Christophe BOETE on 24th June 2010:


    Your argument that the oil spill in the Golf of Mexico is due to environmentalists is really surprising… Given the disadvantages of oil sands (see the example of Alberta) because of the dangers for the environment and the natives, I do not think the environmentalists are the ones to blame.

    On this point we should probably think that the fault is our dependence on fossil fuels and the nature of capitalism that is putting profit before safety and men.

  • Bart Knols on 25th June 2010:

    @Tullu. The resistance issue is as follows: physiological resistance has been observed in many places (i.e. when the mosquito lands on a surface sprayed with DDT it no longer dies). However, Roberts claims that >70% of mosquitoes approaching a sprayed house do not enter it. So whether a mosquito has developed phsyiological resistance is not an issue as long as DDT repels.

    But this is also the weakness of the story - because next to physiological resistance there will also be (or probably already is) behavioural resistance, where mosquitoes are no longer repelled by DDT and enter a house regardless. The same fate is there for pyrethroids…

  • Henk Bouwman on 25th June 2010:

    Hi Bart

    A major misrepresentation of the Stockholm Convention programme on DDT is that DDT is to be phased out by 1017. This is not true. It is only a considered target date for a plan towards phasing out DDT (, and not at all a target of the Conference of the Parties.

    The exact text states: “The hurdles in the future are the considerations of the Secretariat of the Stockholm Convention and do not reflect the views of the Conference of the Parties to the Convention.”

    There is no decision by the COP to phase out DDT at any given date.

  • Henk Bouwman on 25th June 2010:

    Oops…I meant 2017 in stead of 1017. Sorry

  • Bart Knols on 25th June 2010:

    @Henk. The statement that it should be phased out by 2017 I got from the authors and is mentioned in this interview (at 3 min, 9 sec):

    Tren states in this interview “However, there is a deadline that has been set by 2017, where the UN Stockhom convention wants to halt production of DDT and elimination completely by 2020, so no more production after 2017”.

    So he is not telling the truth here?

  • Henk Bouwman on 25th June 2010:

    It is in this interveiw and elsewhere represented as a deadline without any further clarification of qualification. DDT under Annex B of the Stockholm Convention is listed under “Restriction”, not in Annex A that is “Elimination”. For DDT to move to Annex A will need a COP decision. Language that speaks to banning or phasing out shoud be clear on the conditions.

  • Philippe Rivière on 25th June 2010:

    Keep in mind that the “hitler” quote is from a fictitious character in the Michael Crichton novel. Bate and others are much more subtle; you might find an interesting read in

  • Bart Knols on 25th June 2010:

    @Henk. Many thanks for adding this clarification. One more thing: considering that your work and involvement in the Pine River statement was mentioned in the book, what is your opinion that this review was put away as ‘un-replicated, contradictory, or statistically insignificant’?

  • Bart Knols on 25th June 2010:

    @Philipe. Thanks for this link… not much good about Bate. I also found a recent website condemning Tren, asking what he has actually done with his organisation AFM besides lobbying against the ban on DDT…

    I have sent an email to Don Roberts and Richard Tren, inviting them to comment on this blog and the discussion, but so far they remain silent…

  • Henk on 25th June 2010:

    @Bart. I have not read the book.

    To reiterate the conclusions of the Pine River Statement by 15 scientists based on 494 refereed studies. You be the judge.

    “Use restrictions have been successful in lowering human exposure to DDT, but blood concentrations of DDT and DDE are high in countries where DDT is currently being used or was more recently restricted. The recent literature shows a growing body of evidence that exposure
    to DDT and its breakdown product DDE may be associated with adverse health outcomes such as breast cancer, diabetes, decreased semen quality, spontaneous abortion, and impaired neurodevelopment in children.
    CONCLUSONS: Although we provide evidence to suggest that DDT and DDE may pose a risk to human health, we also highlight the lack of knowledge about human exposure and health effects in communities where DDT is currently being sprayed for malaria control. We recommend research to address this gap and to develop safe and effective alternatives to DDT.

  • Bart Knols on 25th June 2010:

    @Henk. I have indeed seen these conclusions at the end of the review.

    I’m sorry - but what does this mean? The study ‘suggests’ that DDT/DDE ‘may’ pose a risk to human health. Does this mean that 494 studies have still not provided conclusive evidence of negative health effects?

    And then, if 494 studies have not tabled sufficient, solid, and conclusive evidence, then what’s the need to call for more research?

    Let me ask a more explicit question: do you personally consider that these health effects do not warrant continued use of DDT at present?

  • Henk Bouwman on 25th June 2010:


    There are a number of issues and I will only touch on some of them. We have submitted a more extensive assessment of DDT for review and are awaiting a result, therefore some points.

    1. Conclusive, irrefutable, cause-effect studies will only be possible with controlled, lab-type, exposures of humans over multiple generations - obviously impossible.

    2. Therefore, you need to assess existing knowledge and judge whether that is conclusive. Obviously, that has a number of inherent drawbacks re extrapolation to say a malaria-type exposure scenario from factory exposures.

    3. Also, newer and more sensitive biomarkers have become available, and we have a better understanding of the various modes of action of biologically active chemicals (say endocrine disruption, but there are more). As we are getting more and better information on how chemicals interact with biology, and more studies are throwing up red lights, than we cannot stop with research, but follow what the data (or its interpretation actually) shows us. Therefore, not only more research, but also better-informed research is needed. The 494 studies in the PRS (Pine River Statement) were only human exposure studies published between 2003 and 2008! This number does not include all the other non-human, environmental, and lab studies published during the same period…and more have appeared since then.

    4. There are, however, very few epidemiological (effects) studies from malaria areas - this is a real and serious shortcoming, and a shame (again, more focussed studies needed).

    5. Lastly, based on all the evidence one can make a judgement. Since more and more studies indicate effects on various systems (not on all mind you, but read the details in PRS), the picture becomes more coherent (read the details in PRS), and it provides for the latest and best-informed assessment on DDT (PRS), but with the added qualifications (this was the crux of your 1st and 2nd questions).

    As to your last question: do you personally consider that these health effects do not warrant continued use of DDT at present? This is not an easy answer.

    Let me quote from another article on active ingredients used for IRS, and breast milk. (Bouwman, H., Kylin, H. 2009. Malaria control insecticide residues in breastmilk: The need to consider infant health risks. Environmental health perspectives. 117:1477-1480. (Supplementary review online))

    “The argument that malaria kills but deaths are not likely attributable to AIs [active ingredients such as DDT] under normal malaria control conditions does not reduce the responsibility to ascertain the risks posed by insecticides and delve deeper into how these risks can be mitigated. Assuming from the above that there is a health burden due to IRS AIs, however small it may be compared with death, it is likely to impose a lifelong (and possibly even transgenerational) disability, handicap, and burden on individuals and society. Malaria control cannot be halted because of these concerns. Therefore, new, safer, and alternative ways of controlling malaria should be pursued, and fortunately this is happening on many fronts..”


    “The eminently practical approach and effective use of chemicals to prevent mortal¬ity and morbidity from malaria is acceptable practice (where other methods do not work) and can be improved on.”

    Please read this 2008 paper, as there are some more arguments in there. There are also more considerations, but this is in the submitted manuscript on DDT and I would rather wait for that, as there are co-authors involved. We are also planning follow-ups on related issues.

  • Donald Roberts on 26th June 2010:

    Thanks for posting your evaluation of our book.  I apologize for the delay in joining the discussion.

    In the next few days I will try to respond in more detail to some of the specific statements and claims.  Let me first say that the reason for the book relates to a need for truth about DDT.

    History of the environmental movement’s tactics and strategies for dealing with dissenting voices forewarned us that the book and its authors would be heavily attacked.  I think your readers can see in comments posted here that the ad hominem attacks are underway.  I know my fellow authors and I can assure your readers that their role and their participation in writing this book was based on a sincere concern about what needs to be done to protect the health and welfare of people in developing countries.  There was no underlying ideological motivation except to make sure that decisions being taken are based on a solid foundation of science.

    We can now look back on a long history of struggles to use DDT in malaria control programs.  This history shows that claims against DDT have been advanced, disproven, advanced again and disproven again.  Each time a researcher finds and publishes some association suggestive of DDT harm—trumpets sound and the attacks rev up.  Activists grab headlines and declare the study proves a cause-effect relationship and that, as a consequence, DDT should be eliminated.  This pattern of anti-insecticide activism also informs us that the activists remain deadly quiet years later when the cause-effect relationship is disproven.

    In a future post I will comment further on statements about the Stockholm Convention Secretariat’s plan for DDT elimination.  The Secretariat is a major operational component of the Stockholm Convention process.  It is disingenuous to suggest the Secretariat’s time line for DDT elimination is not important or that it has no bearing on what will happen vis-à-vis DDT elimination.  The timeline is posted on the Secretariat’s website for the whole world to see and it has huge importance.  What sort of message does it send to the only remaining DDT producer and what should we do about it??

    Bart, I will take time to carefully study participants comments before commenting further.  Thanks again for reviewing our book.

  • Donald Roberts on 26th June 2010:

    Quick follow up comment.
    Bart, you mention a negative impact of DDT use would be to deter the search for environmentally useful alternatives.  Personally, I know of no evidence that what happens with our public health insecticides (either use or non use) influences the search for alternatives. DDT elimination does not, in itself, ensure that there will be a search for DDT alternatives. In fact, if you review the Stockholm Convention positions you will find a commitment to support R&D for a DDT alternative, yet, even as the organization works to eliminate DDT, nothing substantial has been done in the search for a new ai as a substitute for DDT.  Historically, DDT was largely eliminated from programs around the world as a consequence of anti-DDT political and economic pressures, yet there was no serious reflex action to search for DDT alternatives.  Additionally, use of DDT should in no way deter the search for alternatives.

    I think that if you review the track record of AFM advocacy you will find that we lobby intensively for renewed funding to find an acceptable DDT alternative.  In my opinion, such an alternative could indeed be non toxic.  After all, DDT functions mostly as a spatial repellent.

    While we advocate for freedom of endemic countries to use DDT if they choose to do so, we definitely believe that we need a truly efficacious DDT alternative.  Only then should this one-of-a-kind chemical be eliminated.  I personally find it almost criminal that billions of dollars have been spent to, in one way or another, to demonize DDT; yet almost nothing has been spent to find an efficacious replacement.

  • Bart Knols on 28th June 2010:

    @Henk. Thanks for further details. I appreciate the point that better tools to study the fate of DDT have become available. What strikes me though, is that 494 studies between 2003-8 end with a statement full with ‘if’, ‘may be’, ‘could be’, etc. This does not sound very convincing…

    I think nobody will doubt the necessity for a replacement for DDT, and Roberts et al. will argue the same. So the goal is the same, but Roberts et al. want (see his comment) the truth about DDT and its unconditional use for malaria control until a suitable replacement has been found.

    I appreciate how hard it is to really pin down negative health effects of DDT, but unless more firm evidence for this is tabled, it will be hard to negate the points raised in Roberts’ book, don’t you think so?

  • Bart Knols on 28th June 2010:

    @Don. Thank you very much for joining this discussion - I am grateful that you as the lead author of the book, are willing to participate.

    Indeed, the secretariat’s website has this nice horse race cartoon that definitely shows 2020 as the year in which use (not production) will be ended… If this is not what is meant, than the website should be changed.

    Not sure where you got the ‘billions of dollars’ from that were spent on putting DDT in bad daylight, and it would be nice to have some firm evidence for this… Moreover, is the IVCC (Innovative Vector Control Consortium) not blessed with a generous 54 m $ grant from the Gates Foundation? Has Gates not started a project to search for spatial repellents with similar activity as DDT?

    Curious to see your thoughts on this…

  • Graham Matthews on 28th June 2010:

    The debate about DDT is interesting. Can I as a user of DDT in the 1960s in agriculture in Africa make a few comments.

    1.  Back in the early days of DDT extensive testing was carried out in the UK and evaluated by the Insecticide Development panel of the Ministry of Production under the chairmanship of Professor Heilbron (see Journal of the Royal Society of Arts Vol 93 pp65-69 in 1945). Similarly three groups within the USA were assessing the toxicology of DDT. Their verdict allowed its extensive use in Italy and other countries for mosquito control during and immediately after WW II.

    2.  There is no doubt that the public health area needs new insecticides to provide different modes of action as mosquitoes become resistant to pyrethroids. Industry regards the public health sector as only a very small proportion of its market for pesticides so has concentrated on new insecticides with low persistence in the environment, yet for indoor residual spraying and long lasting bed nets, a chemical with a long residual activity is needed.  Changes in formulation and looking back at inventories of insecticides is underway so hopefully there will be alternatives to DDT.

    3.  The real problem was that DDT was so inexpensive that it was over-used in agriculture; for example in the USA a mixture of DDT + toxaphene + methyl parathion was used on cotton at one stage with as much as 4lb/acre/application of DDT applied aerially, no wonder the environment was affected! [In Africa the maximum recommendation on cotton was one lb/acre/application and without the toxaphene or methyl parathion. (the latter was added for boll weevil, not a pest in Africa.)]

    4.  Many of the resistance problems may have been due to DDT and now pyrethroids being used in agriculture and this has affected the larval stage rather than its use as an adulticide in houses!!

    5.  Until a suitable alternative to DDT is available, it seems to me that it should be used inside houses for IRS as recommended by WHO, but what is badly needed is an improvement in the infrastructure of Ministries of Health so that there are more trained staff to manage and use insecticides more effctively in vector control.

    6. Lastly a review of “The Excellent Powder” that I wrote is published in the latest issue of ‘Outlooks on Pest Management’

  • Bart Knols on 28th June 2010:

    @Graham. Thanks for your input in the discussion.

    Point 1: Is refuted by Henk Bouwman in the sense that during the old days the tools to study the impact of DDT on human health were not as advanced and therefore effects may have gone unnoticed…

    Points 2-3: I agree.

    Point 4: Resistance is not an issue according to Roberts and co-authors. The prime action of DDT is excito-repellency, so even if phsyiological resistance occurs, it can still be used for the control of malaria…

    Point 5: Indoor use of DDT. Although this sounds ‘less harmful’ to the environment, I have also come across a study that showed that 60% of the DDT residues come off the walls and are swiped outside local houses when being cleaned. Thus, a lot of DDT still ends up in the environment…

    Point 6: Would love to see your review but don’t have access to Outlooks on Pest Management…

  • Donald Roberts on 30th June 2010:

    Sorry it has taken time to prepare a few comments about statements in posts to your blog.  My focus in the following comments is on technical issues and I apologize if details are a bit lengthy.
    I see from posted comments that there are doubts about our motivations in writing “The excellent powder.” I must say, it seems all too readily accepted that anyone who speaks in favor of insecticides is a shill of the insecticide industry.  That, of course, has been a favorite smear tactic of anti-DDT activists.

    Let me be perfectly clear on this point, I have no connections with the insecticide industry and I know of no private insecticide company that has any interest whatsoever in defending DDT.  Why should they?  They don’t produce, distribute, or sale DDT.

    I am retired and have been retired now for over three years.  I am on the board for Africa Fighting Malaria.  I personally get no pay for writing in defense of DDT, for being a board member, or for participating as a partner in AFM’s work.  AFM has a policy of not accepting funds from the insecticide industry.  To be blunt, there is no financial stake in our defense of DDT that motivates our advocacy.

    I want to comment on some of statements about DDT, bioaccumulation, and actions of other organochlorines. 

    Bart, you state that some chemical actions may not manifest until many years after the chemical was used.  Well, people in the U.S. and other developed countries started heavy use of DDT in mid-1940s.  Then, after almost 30 years of use, they stopped.  It has now been almost 40 years since we stopped using DDT.  During those 40 years, environmental scientists have conducted thousands of investigations, millions if not billions of research dollars have been spent, and vast numbers of papers published.  In spite of all those expenditures and research efforts, researchers still cannot identify any true harm from almost 30 years of heavy DDT exposure.  There was no increase in diseases and deaths during years of its use, and, it is critically important that no health improvements can be attributed to the very large reductions in environmental exposures since that time.

    You state that my argument that chemicals closely related to DDT are present in the environment is weak.  The formal foundation of my assessment is that we now know there is a great abundance of such chemicals and they are natural products, not man made.  The ubiquity of such chemicals means that life evolved in conjunction with natural production and exposure to DDT-like chemicals. Thus, it is biologically implausible that mechanisms for dealing with chemicals like DDT did not evolve as well.  We find evidence of pre-existing capabilities across the whole spectrum of living organisms, from bacteria and fungi (which exhibit a plethora of metabolic pathways for not only degradation but the actual synthesis of DDT-like chemicals) to predators at the top of the food chain (e.g., polar bear does not accumulate DDE).  Perhaps our pre-adaptation to DDT-like chemicals explains why there has never been a documented human death that can be attributed to environmental exposure to DDT or to the build up of DDT in human fat.  In fact, there are no replicated and confirmed epidemiological data showing that accumulation of DDT in human fat is unsafe.

    We make the point in the book that humans will actually accumulate only a certain amount of DDT.  Once an individual reaches a threshold level, all additional DDT will be degraded and eliminated. As for differences among chemicals, we repeatedly make the point that each chemical is different, some being more toxic and volatile than others, some being more persistent and fat soluble than others, and so forth.  I suspect that there is no chemical that is completely harmless; but there are certainly chemicals that are harmless at known exposure levels.  All of these assessments are supported by replicated and peer-reviewed literature.  Yet, in spite of all countering evidence, scientific literature is saturated with papers that ignore these scientific findings and also ignore basic dose and exposure issues, and present data and interpretations as if any residue will cause harm (it won’t) or, that organisms are commonly exposed in the environment to extraordinary concentrations of DDT and other insecticides (they aren’t).  In a subsequent posting I will use a paper from Henk’s research group to illustrate some of the issues of exposure, dose and chemical concentration.

  • Donald Roberts on 30th June 2010:

    The following review of a paper by Dr. Bouwman’s research group is used to illustrate issues of exposure, dose and chemical concentration that relate to claims that DDT is unsafe for human exposures.

    A recent paper by Barnhoorn et al., (2009) deals with comparative levels of DDT in a watershed in South Africa.  Sampling of water begins in an unsprayed region.  Sampling continues as the watercourse traverses a region of DDT-sprayed houses.  The authors cite several studies in the introduction to suggest that DDT and metabolites are harmful in almost every way. Papers cited are mostly experimental animal or biomarker studies entailing administration of very high doses of DDT in order to get a biological response.  I will mention only two of their cited papers. A 1968 paper by Bitman et al., is cited as evidence that o,p’-DDT elicits estrogenic activity in birds and mammals.  This seems to be a favorite paper of anti-DDT researchers.  Of course they never mention that Bitman and coauthors dosed the birds and animals with roughly 180mg of DDT/kg body weight.  Another cited paper (by Kelce, et al., 1998) characterizes DDE as an androgen antagonist and inhibitor of testosterone. Again, there is no mention that the in vivo studies entailed a dose of 100 mg DDE per kg body weight.  Last but not least, Barnhoorn and coauthors do not mention a 2002 paper by Leavens, Sparrow and Devito, which reported that DDE does not produce anti-androgenic effects.  In other words, Leavens and coauthors refute the findings by Kelce, et al.  So a paper that makes a claim is cited and a paper that refutes the claim is ignored.

    Barnhoorn and co-authors then report concentrations of DDT and metabolites in water, fish, birds and chickens.  Overall, 2 or 3 water samples from upriver in the unsprayed area had detectable levels of p,p’-DDE.  In comparison, only 2 of five samples from the sprayed region had detectable levels of p,p’-DDE.  Concentrations of DDT and metabolites were characterized in 28 fish (composed of two species) and all but one was from the sprayed area.  Six DDT isomers were measured in two species of fish as mg of DDT per kg of fish fats.  Of 28 fish, eleven contained the sum of six isomers at concentrations less than 1 ppm.  The average for all isomers in all 28 fish was 7.9 mg of sum DDT per kg of fish fats.  Now, if fish are composed of 10% fat (see:, then 17 grams of fish fat will be consumed in a serving of 6 ounces of fish (28.349 grams X 6 = 170 grams of fish).  This amount of fat will result in 0.134 mg of sum DDT being consumed.  For a 60 kg adult, this will equate to 0.0022 mg DDT/kg of body weight.  Now, to put this into perspective,  doses of DDT in studies attesting to potential harm from DDT exposures that were cited by Barnhoor and co-authors in the introduction varied from 100 to 200 mg/kg body weight.  A similar dose for a 60 kg adult would be 6,000 to 12,000 mg (6-12 grams) of DDT.  Doses administered to the experimental animals were 45,000 to 90,000 times greater than the dose from fish collected in the area where houses are sprayed for malaria control.  In the discussion section, Barnhoorn and co-authors give no weight to the fact that almost as much DDE was found in waters outside the sprayed area as found within the sprayed area.  Additionally, one sample of fish collected on a farm outside the sprayed area contained practically as much DDT as was found in fish inside the sprayed area.  Again, they assign no weight to this observation.  All and all, the concentrations and distributions of DDT reported by Barnhoorn and co-authors suggest that houses sprayed with DDT are not an important source of environmental contamination.  Additionally, the quantities they report for fish should be viewed as trace quantities only and do not represent any threat at all to human health.  The point of this analysis is that the issues of chemical concentration, dose and exposure require much greater thought and analysis than is often seen in studies like that by Barnhoorn and co-authors.

  • Donald Roberts on 30th June 2010:

    Bart, the following comments relate to your assessments about points made in the book:

    You conclude that our statements regarding different organochlorine compounds are weak because, as you state, “as if all chlorinated hydrocarbons are the same…”  Of course we know, and demonstrate through different examples, that there is a great variety of chlorinated hydrocarbons.  Indeed, your assessment would be much more appropriately applied to anti-DDT advocates.  Those advocates commonly group all man made organohalogens together, characterize all their potential harms, then carry those characterizations over to DDT alone. In fact, DDT is not dieldrin, aldrin, a PCB, a dioxin, or any other organohalgen.  It is unique among all those compounds and only DDT has proven efficacious in the long-term control of malaria.  Additionally, our comments and comparisons were made in part because there is strong opposition to chemicals that contain halogens, and chlorine in particular.

    You attack us for saying that if people’s children are being killed by malaria that they will tend to have more children to offset those losses.  Your actual statements were: “Finally, and this argument will upset many, they claim that because of malaria, African families compensate for children lost to malaria by producing more. They than [sic] crawl under the skin of an African person saying ‘They may think “we must do something about this disease before we lose more of our children”. This is a pretty far-reaching conclusion (particulalry [sic] in view of the availability of bednets).”
    I must say that it seems your analogy is designed to inflame Africans.  Additionally, your statements misrepresent my position on this subject.  Misrepresentation stems from the fact that my assessments were not about Africans.  My geographical area of expertise is South and Central America, not Africa.  My fellow authors, on the other hand, have greater expertise in malaria control in Africa.  The quote you refer to is about all malaria endemic countries, not just African countries.  The sentence you quote from the book was put there to trigger an explanation why it is not within the grasp of normal people as individuals to do much about malaria without improved standards of living or the use of insecticides.  As for your comment about bed nets, remember, this book records the history of what happened with DDT.  The environmentalist’s battles against DDT that ended effective malaria control programs were fought decades ago and there were no insecticide treated bednets at that time.  If we bring this issue up to modern times, it is worth noting that many people have been selling and hyping bednets to the practical exclusion of any other method of malaria control since the late 1980s, yet we still have very large numbers of children dying from malaria.  Given this reality, I don’t think our conclusion is far-reaching at all.

    As for whether people will have larger families if large numbers of children are dying from malaria, I stand behind assessments in the book.  I compiled historical data on fertility rates (plus data on other variables) for countries with and without malaria. I produced the correlations; but unlike the anti-DDT folks, I do not assume a correlation or statistical association proves a cause-effect relationship.  Human fertility is a complex issue that is influenced by many factors.  Regardless, in my opinion, it is naïve to think that if 2 of every 4 children are dying from malaria that such losses would not factor into decisions about family size.  After all, those deaths are not something they just read about, they are part of everyday life.  Poor people want their children to grow to adulthood and they hope for grandchildren too.

    As a last comment, to prove that behavioral resistance has occurred, you would first need to engage the issue of how the chemical actually functions in the first place.  So far that has not been done in a meaningful way.  I agree that behavioral resistance could be a consequence of DDT use; but it cannot be accepted as an important issue until we have a lot more knowledge and information than we have today.  The ultimate truth is that DDT functions primarily as a spatial repellent and it is still highly effective in control of malaria.

  • Richard Tren on 30th June 2010:

    Thank you Bart for reviewing the book and starting this discussion.  Prof. Roberts has done an admirable job of responding to some of the comments and so I will respond to just some of the statements.

    @Christoph Boete raises questions about our funders and Prof. Roberts has responded to this.  Let me reiterate that we have never received any funding from the insecticide industry and we will not accept funding from this source precisely because people will immediately assume that we are simply shills for industry and will dismiss any substantive arguments.  Not only are we not funded by the insecticide industry, but we have been openly critical of them when they have tried to limit the use of DDT so that they could sell more of their own product. So the very idea that private industry somehow has a stake in the DDT issue is absurd. It is depressing that some people seemingly assume the worst motives when an individual or group defends the use of DDT, yet never assume any ulterior motive among those who attack DDT.  Why is it, for instance, that no one raises the fact that anti-insecticide lobby groups are funded by the organic food industry. (and quite a growing profitable industry it is!) When they conduct their anti-insecticide campaigns, confidence in conventional farming decreases and the organic food market grows along with their profits – yet these corporate interests are seldom questioned.  Furthermore to assume that those funded by government institutions or foundations are without their own selfish motives is naive in the extreme.

    AFM has received some funding from a couple of mining companies.  Both BHP Billiton and Anglo American have funded outstanding malaria control programs (separate from AFM funding), saving thousands of lives and they should be applauded for their work.  AFM is proud of its association with these companies and grateful for their support.  Exxon Mobil gave a small donation to AFM several years ago for general support for which we are grateful.  Similarly this company has supported some excellent malaria control programs as well as research projects.  Exxon Mobil is a donor to the Medicines for Malaria Venture and many other malaria advocacy and research groups. Does this support mean that MMV and all the other groups that Exxon Mobil funds are somehow tainted or illegitimate? Of course not.

    @Philippe Riviere links to a scurrilous ad-hominen attack on one of my colleagues.  These are not new – it seems that if you are going to defend the use of DDT and criticize environmental activists (who seem to be considered royal game and individuals with unquestionable motivation of the highest order) then people will muck rake and try to find any and all opportunities of undermining you.  We prefer to get on with our work and ignore those who wish to snipe from the sidelines.  Having said that, I recently had to describe in a blog post questioning our work here:

    @Henk Bouwman takes issue with statements we have made about the Stockholm Convention and the Secretariat’s intention to halt all production of DDT by 2017 and eliminate all production by 2020.  I would like to add a comment to Prof. Roberts’ answer.  We include in the book an analysis of the representation at the Stockholm Convention meetings – note that overwhelmingly those countries that use DDT are outnumbered by wealthy OECD countries that no longer need DDT and by anti-DDT activists who expertly lobby and influence the proceedings.  Also remember that most of the representatives from malaria-endemic countries are not from the Ministry of Health that may have some knowledge and understanding about the need for DDT, but from the Ministry of Environment (i.e., people who prioritize environmental protection over public health).

    And while we are on the topic of statements made during interview, perhaps Prof. Bouwman can finally provide the evidence for which we have been asking for relating to statements made on South African television that DDT is linked to harm to fish, snails and possibly birds.  Prof. Bouwman even links DDT to a specific case of intersex in the South African athlete Caster Semenya.  Please note that we asked for the evidence for his statements and were joined by several others, including scientists at the CDC and USAID.  (I’ll be happy to forward the email trails to anyone interested) To date we haven’t had any response.  Perhaps Prof. Bouwman is ready to provide the evidence for his statements here – or to retract them if he doesn’t have evidence that DDT is linked to the intersex case of a named individual, Caster Semenya.

  • Bart Knols on 01st July 2010:

    @Donald-first comment. Thanks Don, for adding more information in this discussion.

    Let me tell you up front that your book has certainly changed my views on DDT. As a young biologist I was brought up in University with the info that DDT was the worst thing mankind had ever come up with, until, almost in a fairytale-like manner, Rachel Carson appeared on the scene. I am convinced that the current generation of biologists is still being trained in the same manner, so you’re up against hordes of people with a dogmatic believe that DDT is bad.

    As you state early on - this is about finding the truth.

    I have never assumed that you or any of the co-authors of the book had any commercial stakes in DDT, so that’s no issue from my side (although others will remain suspicious…).

    As for delayed effects: You are right, millions of kg of use in US agriculture did not result in some liver cancer epidemic ten years later. But the more subtle long-term effects will, no doubt, be more difficult to discern. This is not just an issue with DDT, but pops up in any discussion about products (not just chemicals) in terms of environmental risk assessments.

    As for the parallel evolution of man with DDT-like compounds, I am still not with you. You know that changing a simple methyl group in a chemical can turn it from benign to carcinogen or into a deadly toxin. That’s why I find the comparison table salt and DDT not very informative. Salt has chlorine in it - and we consume lots of it every day. But we die if we drink seawater which has the same compound.

  • Bart Knols on 01st July 2010:

    @Donald-second comment, ref Barnhoorn article (2009) - your argument here is convincing, and I hope that Henk Bouwman will chip in if he is not in agreement with your views.

    @Donald-third comment.

    Up front: ‘You attack us…’ is not the way to go. This is not my intention. My intention is to get to the truth, which is what we have as a common goal here.

    I also have no intention to inflame any African person. My argument holds for any person living under the burden of malaria. My point is that I would like to see the truth (again) that your view on this is correct - what information is there to substantiate the point that malaria ranks high on people’s agenda in terms of ‘safeguarding against possible losses of children’. Having worked and lived in Africa for 11 years, I have not come across such thing - in other words, what I am trying to say, is that this may not be the best way to make a case for DDT (you have many much better justifications in the book than this one…).

    As for behavioural resistance: I think that anyone who has read the book will have to agree that a list of 12 pages of studies demonstrating the repellent effect as the main mode of action of DDT is convincing.

    My point is that the same has been said for synthetic pyrethroids that supposedly also have excito-repellent action. But, it is disappearing from places where it was present before. And this is not a surprise. The same fate will be there for DDT - there is absolutely no doubt. Ultimately you will have behavioural resistance and physiological resistance and the story will be over.

    Recently, the Rothamsted group published a paper in PNAS, showing aegypti building up behavioural resistance to DEET over a number of generations. Without wanting to make a direct comparison between DEET and DDT, this does however show the resilience of insects.

  • Bart Knols on 01st July 2010:


    - See my comment ref your involvement with the pesticide industry above.

    - I have mentioned in my blog that you and Don, Richard and Jennifer stand out from the crowd that is simply not willing to change its opinion towards DDT. That this leads to people seeking all sorts of motives to attack you on a personal level is unavoidable. Again here, as Don states, it’s all about getting to the truth of the matter, which was the prime reason for me reviewing your book here and bringing it to the attention of the broader public.

    - Ref your last point, the ‘intersex’ issue and urigenital defects in Limpopo, SA, I would like to see Henk’s response here too. Henk?

    Recently I contacted the Greenpeace HQ in Amsterdam and asked them for their opinion on DDT, GM mosquitoes, and the Sterile Insect Technique (that uses a nuclear source to sterilise mosquitoes). They cling to dogmatic views and it is very hard indeed to have an open well-informed discussion. See my blog on this:

  • Eric Ndofor on 01st July 2010:

    There is no chemical with a zero negative impact/effect on the environment and human health; DDT may be useful but we need thorough and comprehensive environmental and health impact assessments. Any articles on this? I also don’t understand if DDT is being banned because it is controvertial or because it is more dangerous than useful. What are the hard facts about DDT?

    Personally I think the elimination of malaria depends on an integrated approach including strong political committment, socio-economic intervention (elimiate poverty, habits, etc), environmental control (proper hygiene/sanitation) and medical (proper diagnosis and effective/complete treatment), and research.

  • Bart Knols on 01st July 2010:

    @Eric. Thanks for commenting.

    - There is indeed no chemical that is completely benign - water (H2)) can kill. It’s all a matter of dose.

    - The dispute about DDT has been centered on the interpretation of scientific data. Many argue that there is sufficient evidence to ban it because of environmental and human health effects. Some (like Prof. Roberts and co-authors) claim the opposite. Read the Pine River Statement referred to above for one view, read Roberts’ book for another. Both claim hard facts to work either for or against DDT.

    - I don’t think anybody will argue against your suggestion for an integrated approach to the control/elimination of malaria. It’s merely that some want to see DDT as part of that, whereas others will fight to the bitter end against it…

  • Donald Roberts on 01st July 2010:

    Yes, perhaps the word “attack” and harsh response was unwarrnated, my apologies.
    We really appreciate the fact that you are hosting this important debate in a responsible and open way.  We may differ about DDT-like chemicals, but we fully agree that, as you mention in a response to Eric, that the dose makes the poison.  We look forward to further comments and reactions.

  • Bart Knols on 01st July 2010:

    @Don. Thanks, and no hard feelings. I am hopeful that this discussion opens people’s eyes to get to the truth about DDT, and that a common understanding that judgement based on ideology is not the way to go in such matters will hopefully be the result.

  • Daniel Nylin Nilsson on 07th July 2010:

    It was quite [url=“”>predictable</a> that DDT would become a discussion on Think 3.

    It is a complex issue of course. DDT is a poison, that is why insects die from it. It is also harmful for humans. If the city council decided to spray your house with DDT, would you agree? If you had kids? IF you say yes -would you be able to convince your wife? Many people would not - and this is a major flaw with DDT. In order to be efficient EVERY house in a village must be sprayed,s o there can not be much of a choice for those who live there (what if they are ‘environmentalists’).

    On the other hand - Malaria is a horrible disease, and we know for sure that DDT works against it for a period of time. So what we are choosing between is not a good thing or a bad thing, but between a bigger or lesser evil.

    But please, please, Bart, do NOT bring up idiots like these :( We had more than enoguh of anti-science propaganda on think 2. The sources behind this are those the same that oppose climate change, and any kind of environmental legislation, which has been written about in a book that mades lots of headlines recently - Merchants of doubt.

    Where does this anti-scientific resistance come from? I believe it is from a libertarina conviction, that can’t accept that human inventions can be harmful - that’s why climate change MUST be impossible, that’s why DDT MUST be a healthy and efficient.

    As for @Tullu -to say that environmentalists endorsed off shore drilling is a blatant lie. Shame on you! It was a decision Obama took, and was <a ]critizised[/url] for by environmentalists. And who was it who coined the slogan ‘drill, baby drill’ before the election? The environmentalist Sara Pahlin. Is it maybe Greenpeace you want to replace Obama with?

  • Bart Knols on 07th July 2010:

    @Daniel. Thanks for chipping into this debate.

    Up front, I guess that you have not read the book this blog is all about. Hence, your views have been influenced by what you heard and read about DDT in the press. You have based your opinion on the slogans and statements thrown around by either the pros or cons regarding DDT. And that’s precisely the mistake that you make.

    What Roberts and co-authors try to accomplish is to develop a meaningful debate that is governed by scientific information and NOT by feelings or perceptions. This is definitely to their credit. Getting to the truth about DDT is much better than anyone’s up-front uninformed ‘knowledge’ that DDT is harmful to humans. You lack the basics to substantiate these statements (and if so, please post that information here).

    The people you classify as ‘Idiots’ (I regret your disrespectful approach here) are not at all refuting science - on the contrary, they use scientific information to back their arguments.

    As for malaria control to be efficient, the common understanding at the moment is that coverage of 80% or more is sufficient to have (mosquito) population level effects. Your capital letters ‘EVERY’ is not correct. Sorry, my information is simply based on scientific facts, not on ideologies.

    Clearly, I am sorry to say, you are misinformed about this matter. Confusing this matter with climate change is completely irrelevant, and your conviction that the authors of the book claim that DDT MUST be healthy is simply not correct.

    Before you come back with another comment, could I please request that you read their book first?


  • Daniel Nylin Nilsson on 07th July 2010:

    For a discussion of DDT effects on humans, see Eskenazi et. alt. - The Pine River statement. I quoute from the conclusion:

    “We are concerned about the health of children and adults given the persistence of DDT and its active metabolites in the environment and in the body, and we are particularly concerned about the potential effects of continued DDT use on future generations. We recognize the serious implications of restricting DDT use given that an estimated 880,000 people die each year from malaria, most of whom are < 5 years of age (WHO 2008).


    “Current evidence on DDT exposure to human populations and on its potential health effects support the Stockholm Convention on Persistent Organic Pollutants, which emphasizes that DDT should be used with caution, only when needed, and when no other effective, safe, and affordable alternatives are locally available. ” 

    @Donald - “poison” was manybe the wrong word. My point is that DDT is something that stays in my body and is carried on to my children (see link above). No matter how much salt I eat -my children will not be born with increased level of salt in their bodies.

    I apologize for using the word “idiot”. It is right - we should take care to keep the debate clean and worthy.

    But are you not aware about the connections between climate change denial, denying that tobacco causes cancer and the pro-DDT lobby? Just take a look at the amazon link you provide - what other books did the people who bought this book like?  Power Grab: How Obama’s Green Policies Will Steal Your Freedom and Bankrupt America , The Great Global Warming Blunder, Climategate, and the book I refer to above, Merchants of doubt. See also what sourcewatch writes about Richard Trent

    The DDT discussion is not only about chemistry, it is a very tense political field, and a very symbolic issue. Both for environmentalists and for right wing libertarians. I would like to hear your thoughts on that.

    Meanwhile, I will try top find Robert’s book wink I will post again after reading it.  I would get

  • Bart Knols on 07th July 2010:

    @Daniel. Thanks for getting back - although before you read the book…

    The Pine River Statement conclusions were mentioned in the above blog, and it remains unclear why a review of nearly 500 studies that were conducted between 2003-2008 are concluded with ‘ifs’ and ‘maybes’. I would assume that 500 studies on the possible negative effects of DDT would deliver a more firm verdict. Instead, as mentioned in the discussion above, it is argued that more research is needed…even more research? That sounds a bit strange to me, given the number of studies already published. But alas, I stand to be corrected here.

    We accumulate lots of different chemicals in our body. The point that Roberts et al make is that millions of people have been exposed to DDT (sometimes in high concentrations) and that no negative healthe effects have been observed…

    The link that connects climate, smoking, and health is meaningless to me. Here we are dealing with the intricacies surrounding DDT, and I frankly don’t care who is behind what lobby (whether they are conservatives of democrats will change nothing to the science of DDT). Let’s not blur the discussion with personal or political statements but face the facts.

    Having read the sourcewatch piece about Tren, I must mention here that the relationship between climate change and malaria is indeed, as he argues, still being debated. That Tren has been involved in tobacco stuff is simply not relevant to the discussion here. Focus and evidence, that’s more important.

    That DDT is a controversial chemical nobody will deny. I repeat myself by saying that what we need is objectivism, and not a debate driven by ideologies and activism.

    Thanks for reading the book. I look forward to seeing your views here after you’re done.

  • Bart Knols on 08th July 2010:

    For the record - as this may not be clear to all reading this discussion - DDT is currently being used on a large scale for malaria control in Africa. At least 15 countries have had more than 6,5 million houses sprayed between 2005-2009, with funding from the President’s Malaria Initiative (PMI) and administered by USAID. The impact on malaria has been dramatic.

    The concern that remains is that in most places this has been a one-off spraying campaign, delivering short-term benefits only.

    A major problem at the moment is that DDT is administered through vertically organised and centrally staged control campaigns, the infrasturcture of which is lacking in most places where reliance on house-hold based methods like bednets, has become commonplace.

  • Daniel Nylin Nilsson on 08th July 2010:

    @Bart I think it is hard to get a clear verdict on persistent organic pollutants, since their effects depend so much on what substances they interact with etc. But after 24 hours of googling, yes - it sems that DDT is relatively safe for humans but very dangerous for the ecological system. “Roberts uses 432 pages to tell us that the greens lied to us about the fate of the Bald Eagle, the peregrine falcon and robins during the period that DDT was used widely in US agriculture. He blames hunting and habitat loss instead of DDT and uses page after page to show us he is right.” - He is not right about this. Can you find any kind of authoritative source saying this? I don’t think any biologist with knowledge about birds would agree about this.

    In Sweden, and I guess also in teh Netherlands we have several raptor birds and sea mammal that were close to extinction in the -60’s, without any of the factors Roberts mention here. All of them eat fish, and I guess you know why - DDT doesn’t stay in water, but is consumed by waterdwelling species, like fish. The concentration then gets extremely high in the top of the food chain. There is no other plausible explanation to these animals decline, than the insecticides and pesticides that were in use in agriculture, but of course it is extremely difficult to say what effect DDT had, compared to the effect of quicksilver etc.

    I strongly advice you not to be naïve about these guys. Do you know the site ? It is run by a man called Steven Milloy, who for years have been spreading disinformation about climate change. He has no interest in malaria - his interest is to protect big business from the public.

    @Richard, I don’t stick the label “idiot” to anyone because of his or her opinion. What I referred to is the kind of conscious lying that goes on on sites like junk science. I am sorry if I was not clear about this.

    Yes, I guess one could add a line or two about Hugo Chavez. But I think you also see that there are links to his opponents further down the site?

    Sourcewatch has an agenda, of course, and that is to provide information on the kind of desinformational sources I mention above. I promis you - if you ever want information about climate change denial, that’s the best place to find it.

    I didn’t write that you as a person were connected to the tobacco business, and you are not mentioned in the post I link to.

    Sourcewatch claims that you are the author of Smoked Out: Anti-Tobacco Activism at the World Bank: A review of: Curbing the Epidemic: Governments and the Economics of Tobacco Control, World Bank, 1999. I presume this is the publication you mention?  My opinion? Well… that tobacco is not necessarily the most unhealthy thing an individual can choose to do, but that it kills 2.1 mn people annually in the developing world, and 4.2 mn globally.(WHO)

    Thanks for updating me on your activities in Uganda.

    I am glad to see that AFM does recognize that ther is such a thing as man made warming. I agree - it’s effects are very diverse and impossible to predict. And the spread of malaria is probably not the most worrying thing about climate change. I would be more worried by loss of biodiversity, and this is also where I see a problem with DDT use. BUt I understand if the spread of malaria is what is your organization’s focus.

    Where you get funding from is clearly visible on your website. I do think that it would be a massive strategic mistake for the tobacco industry to fund you. Just imagine what left wiung environmentalist bloggers would be writing.

    As I wrote in my first comment, I don’t think that there are big financial interests behind pro-DDT writers “I believe it is from a libertarina (sic!) conviction, that can’t accept that human inventions can be harmful - that’s why climate change MUST be impossible, that’s why DDT MUST be a healthy and efficient.

    Yes, these debates - DDT, climate change etc. have been completely devastated by “Scurrilous ad-hominem attacks”. Remember the fuzz about climategate? In such heated debates, words easily slip. I am not proud over using the word ‘idiot’ here. As I have already said, that refers to the junk science mafia - not to anyone thinking that DDT is a valuable tool against malaria.

  • Daniel Nylin Nilsson on 08th July 2010:

    I have a few questions for both Bart and Richard:

    1. What is new about this? Is the information and the statements in The excellent powder in any way different from what Tina Rosenberg wrote in 2006?

    2. Why do you refer the disappearance of malaria in the US to DDT spraying? It seems to have been more or less gone in the US even before second world war. If you have better sources than me, please tell me. I admit I can be wrong about this one, but there are also countries where malaria disappeared even without DDT spraying, e.g. Sweden. So DDT can not have been the only reason.

    3. Noone is questioning that DDT is a realtively cheap and efficient way to fight malaria. Likewise no one I have come across, except for The excellent powder, and Steven Milloy, claim that DDT was NOT harmful for birds, did not harm their eggs etc. Not even Rosenberg in her article. What is the sense of bringing up this one, which will not exactly make it easier to work for increased use of DDT?

    4. @ Richard. DDT has never been banned against malaria, and is being used today. What is it that you are working for? That it should be employed even outside the inside residual spraying? Or that more houses should be sprayed? That it should not be banned from use in agriculture?

    4. @Bart As a malaria expert, what is your view? How much DDT can we use without endangering biodiversity and human livelihood?

  • Bart Knols on 08th July 2010:

    @Daniel. Thanks for coming back once more - again without having read a page of the book (yet).

    Roberts et al use a lot of background information in their book to describe what actually happened to the raptors, and what caused their decline. You, without having read any of this claim ‘He is not right about this’. What makes you say this? Let me put this the other way around: if you claim that they are wrong, then provide the evidence for it. That will help this debate. I find it very hard to accept your verdicts without you having ploughed through the evidence, be it for or against the case.

    The same applies to your verdict: ‘There is no other plausible explanation to these animals decline, than the insecticides and pesticides that were in use in agriculture’. Where do you provide justification for this statement?

    Finally, when you say ‘I strongly advice you not to be naïve about these guys.’, you of course mean to say that I am naive in this matter. Well, I have 20 years of research in the field of malaria under my belt. In the blog I mentioned that I was brought up with the same belief that DDT is all bad news. After reading ‘The excellent powder’, at minimum, I found it sufficiently compelling to open a debate over DDTs pros and cons. Nothing naive about that…

    In your last comment you ask for my personal opinion. Up to this stage I have tried to avoid giving my personal view on DDT. But since you ask, let me put myself in the position of a rural Zambian family, void of virtually anything you or I have at our disposal. Having worked in a tsetse elimination campaign in Zambia for three years, I have seen some dramatic examples of poverty and starvation. If I was living under such extreme conditions and I would be given the option to have my house sprayed with DDT I would say ‘Yes, thank you’. It may all be good for us (you, Don, Richard, Henk, me) here to discuss the pros and cons of DDT, the fate of birds or polar bears, but in the real world people die like flies of malaria. Hard to argue against DDT from that perspective…

  • Daniel Nylin Nilsson on 09th July 2010:

    @Bart Why I can calim that DDT did in fact casue egshell thinning in raptor birds: (The critical substance is not DDT, but the breakdown product DDE)

    1. This is the mainstream opinion among biologists, that has held sway for 30 years. in spite of being challanged. See for example this excerpt. But I think you know this as much as me.

    2. In telephone conversations with sources in the regional ornitological assopciation, a man who has decade long experience of working professionally with ecological matters, and the researchers occupied with this subject on the Swedish Museum of Natural History I have been told that this, and adviced to not get into this discussion :/ These researchers highlight another important matter - the problem was not restricted to DDT, but to the general use of pesticides. Maybe we have forgotten today how they were once used… just take a look at the Carson-clip you posted.

    This means that a DDT use that is restricted in a way that it does not reach the environment can easily be acceptable. But is there any research done about any possible effects on biodiversity from IRS?

    There is however no discussion about the fact that pesticides, among them DDT, did threaten raptors, severly, and cause eggshell thinning.

    3. Can you think of any other reasonable explanations to the story of the Swedish raptors?`How can it be that within 15 years of the mass introduction of pesticides like DDT, almost all our big raptors were endangered, as where seasls and otters? And that massive amounts of DDT and other pesticides were found birds, seals and otters? Unlike the situaton of the bald eagle in the US, these birds where not hunted, or threatened by land use before the second world war.

    You must have similar stories from the Netherlands, also?

    I deeply respect your knowledge as a malaria professional. But are you not at all worried that people like Milloy are trying to hi-jack your movement, and that they try to link the pro-ddt discussion with climate change denial?

    In case you want to stay clear of politics and focus on the intricacies surrounding DDT, you must either avoid the political subjects, or take some sort of critical stance towards them. You know as well as me that ther is a hate campaign going on against Carson, and with that knowledge you can not simply reproduce statements about here without some sort of critical assesment of these statements.

  • Daniel Nylin Nilsson on 09th July 2010:

    Here is a good link on the political sides of the debate, and the hatred for Carson.

    In a situation that you describes - oh yes, I would also ask to spray my house with DDT, if that was the only choice I was offerd. but I would prefer a bed net. Especially I would prefer a bed net that I had bought myself - that would free me from dependence on someone else to come spraying my house. Can you guarantee that there will still be funding to maintain IRS programmes until malaria is gone?

  • Bart Knols on 09th July 2010:

    @Daniel - thanks for getting back for the third time without having read a page of the book (you note that this becomes repetitive, but it does signal a message to you…).

    - If you read the book you’ll get the details about DDT, DDE, etc.

    - You mention that ‘mainstream opnion amongst biologists’ as the fundament on which to conclude that DDT was a prime culprit with regard to the decline of raptors. For a long time people were convinced that the earth was flat…those that argued otherwise were condemned.  Even if opinions are ‘mainstream’, does that mean that they are therefore always correct?

    - If you are advised ‘to not get into this discussion’ you reach the heart of the debate. People not willing to discuss this matter openly, chip in scientific evidence, and contribute to a productive discussion, apparently have something to hide…

    - I assume that you read Don’s latest comment. He mentions acute poisoning of birds immediately after area-wide spraying of DDT. In the book it is also mentioned that eggshell thinning did occur because of DDT, but that this was NOT the prime reason for the decline of raptor populations.

    - I have no insight in the possible causes for the decline of raptor populations in Sweden (or the Netherlands) but loss of suitable breeding habitat certainly affected various species in Holland.

    - Regretfully, DDT is being viewed as a ‘left wing’ versus ‘right wing’ political dilemma. If Milloy tries to link the pro-DDT discussion with climate change denial, so be it. This does not have my interest. What does interest me, is getting to the truth about DDT. ‘Hate campaigns’ are not bringing us anywhere forward, the point is that Carson’s views and claims in Silent Spring have been scrutinised and evaluated in terms of scientific merit. If her claims have been refuted on solid scientific grounds, than you may tell me if this should be considered as a ‘hate campaign’. I don’t think so.

    - Carson has done what many people argue to be a good thing, she got the environmental movement going. That this movement is now there in a multitude of forms is grand, and I am happy about this. That the movement uses ideologies rather than solid scientific information as the basis for their activism, is something I regret.

  • Daniel Nylin Nilsson on 09th July 2010:

    @Richard What I, as a lay person can not really come to terms with is how the sprayee substance can stay indoors. Doesn’t this require that people don’t replaster their walls? What happen if their house is torn down, don’t the substances in the walls leak into nature, etc. ?

    Insecticides is one threat against biodiverstiy, but as you highlight ther are also other. In the end the fundamental problem that we need to solve is povert. What is common for all countries that have liberated themselves from malaria, with or without DDT, is a prolonged period of economic growth. But of course there is also a point that malaraia creates poverty. Reality is complex.

  • Daniel Nylin Nilsson on 09th July 2010:

    @Donald I read your paper, thanks!

    You mention well-funded environmentalist movements. This came quite as a surprise to me, usually we think of environmentalists as hyouthful enthusiasts, with a sever lack uf funds. Who provided the anti-DDT campaigns you write abou with funding?

    I wam waiting for the book, as yo understand I must ahve it shipped from the US.

  • Daniel Nylin Nilsson on 09th July 2010:

    @Bart I get your message, but many intersting questions have came up here, that do not exactly require reading the book so… but I will, don’t worry.

    The scientific community never held the opinion that the earth was flat - that was a prejudice.  Of course the mainstream can be wrong, but I think that the academic science is in general more trustworthy than people think of it.

    I do not think that her claims have been refuted on solid scientific grounds. It is truly sad that issues like these tend to degenerate into a lef-right brawl - that is why it is extremely important to draw a clear border towards those who want to abuse the issue.

    Carsons book in deed spurred many things, and as an irony of history I think it also spawned her contemporary opponents smile In society there is a much bigger willingness to challenge established truths (see our discussion here for example). This is not only due to Carsons book for sure, but it played a big role in the general anti-establishment thinking in the late -60’s. Which has created space for a much more radical right wing.

  • Bart Knols on 09th July 2010:

    @Daniel. Interesting point. I have also heard that even when DDT is sprayed indoors on plastered walls, that a substantial amount is being swept out of the house when the plaster comes off the wall, and is brushed outside. I remember a figure of 60% within 6 months after spraying, but cannot recall the reference where I picked this up… Anyway, perhaps Don can enlighten us on this one.

  • Bart Knols on 09th July 2010:

    @Daniel. Just read the science blog: Taking aim at Rachel Carson. When you read The Excellent Powder, please pay attention to the prime working mechanism of DDT: repellency. There are some 12 pages in the book listing studies from all over the world, that the prime mode of action is repellency, not killing. Puts the resistance story in the above article in a completely different context, agreed?

  • Bart Knols on 09th July 2010:

    See recent comment on DDT by Drs. Hans Herren and Charles Mbogo here:

  • Daniel Nylin Nilsson on 09th July 2010:

    @Bart Agreed. I think the repellancy is maybe the most intersting part of their claim as I understand it today.

    Pretty harsh words in this review wink

    I think I will do us all a favour if this is my last ccomment, and I rewturn after having read the book. Ciao for now! smile

  • Bart Knols on 09th July 2010:

    @Daniel - many thanks for your contributions in this discussion, and indeed looking forward to see if your views will have changed after reading the book. Have fun with it!

  • Daniel Nylin Nilsson on 09th July 2010:

    I promised not to come back, but I can’t resist wink

    The thing about Caster Semenya was completely new to me, but that sounds really eird. Regrettabel in deed.

    They were mentioned at the time. The reason that DDT is in focus now is exactly that it can be used against malaria, and that’s why you have writers like Don and Richard propagating for using meore DDT, and other people propagating against it.

  • Bart Knols on 09th July 2010:

    @Maureen. Thanks for chipping in. Funnily enough, I have the impression that if there would have been a strong lobby for IRS with dieldrin or BHC, that the amount of resistance from the environmental movement would have been much less, in spite of higher toxicity of these compounds. It’s the problem with DDT. As soon as these three letters are mentioned, all rationale subsides and classic statement surface without any justification.

  • Bart Knols on 09th July 2010:

    @Donald - thanks for this additional information. What is your response to the Herren/Mbogo letter in EHP?


  • Bart Knols on 09th July 2010:

    @Richard - thanks, I had not seen your reply. I have invited Hans Herren to also review the discussion here and contribute. I hope he will.

  • Daniel Nylin Nilsson on 10th July 2010:

    Regarding the environmentalists and teh Stockholm convention. I looked at the loist of partner NGO’s. As you say there are environmentalists, and business representatives like the us semiconductor industry association, the Russian chamber of commerce etc. Did AFM apply for accreditation, or do you think that you were excluded? It is quite obvious why teh environmentalists want to be there, don’t you think? If I understand matter right, the NGO’s have no formal decision making right. I presume you lobbied the US government instead, which probably would be a better strategy wink - I can see that the US has not ratified the convention.

    There is no doubt that there were many well-meaning, skillful and innovative professionals working with these matters. What I talk about is the political perception. A lot of people in the early 60’s had a sense that society was being run not by the people, but by a faceless and emotionally cold bureaucracy. The environmentalist movement was only one of many anti-movements that fundamentally changed the way we think about authority in the west.

    When people had this perception - and they saw dead fishes in rivers next to them or on TV, the DDT and pesticides issue must have seemed like an abuse of power. Also remember that ther was a lot of insiecurity about the New Deal heritage, and strong currents in american society that would be against professionals and authorities on rather ideological reasons. You find a lot of such anti-establishment-ism in Carsons book, for example.

    You get my point? I am not saying that the professionals did mistakes, but that people where afraid of what these professsionals would do to their lifestyle.

    As you say DDT and pesticides were widely discussed, aand there were laws restricting its usage, reasearch about connections to cancer etc. basically from day one. And I am one of those who would not see the beginning of environmentalism in the 60’s, albeit if the movement grew in the 60’s.

    “Given this fundamental truth, I don’t think developed countries and UN organizations should have the authority to deny countries a fundamental right to use DDT in the protection of their own people.”

    - that is a big discusion, which is very relevant for this blog. What you are calling for is a different way to handle things like these, outside the UN.  I think that developing countries if anything are weaker to defend their rights outside the UN. Think about it - at the moment developing countires have guidlines from the WHO saying that they should use DDT against malaria. Of course the UN is far from efficient, but the alternative for aid-receiving countries would be to depend fully on volatile opinions in the west. Which politician do you think would be the most popular in Sweden, one who says thet Swden will help fund DDT campaings, or one who promises to fund resarch on alternative methods to fight malaria? Which politician do you think would gain most popular support in the EU?

  • Bart Knols on 12th July 2010:

    A person with the name Roger Tatoud left the following comment on my LinkedIn page:

    Roger TATOUD has just left a comment on your network update:

    “One of the author of this book has little credibility in my view (Bate). I leave the Malaria science to you but would be cautious about their interpretation. If you ask why me they would write such book the answer is very simple, as you guess it: Money.”

    It is funny to notice that people seek answers regarding ‘The excellent powder’ from the perspective of the authors. They simply conclude that arguing in favour of a chemical must mean that the authors have commercial interests.

    This has been refuted by Donald and Richard in this blog, and I have no doubts that this is true. There is no major business in DDT, so why would the authors write a book about it?

    Next, by attacking Bate without sticking to the main argument that focuses on DDT, it again shows how fighting for a cause quickly turns into personalised attacks. I hoped that this discussion here would get us beyond that point, but alas, it is hard to change the world…

  • Bart Knols on 15th July 2010:

    Today I received the following information by email from South Africa:

    DDT –

    This company (Regent laboratories) works closely with government agencies on the ground across southern Africa on a day to day basis.  Here are some of the findings.

    Is there too much talk about the rights and wrongs of the use of DDT? Also, is there too much hype as to its harmful use and future health issues without the overall picture as today’s challenges looked at in detail?

    Some facts which are not readily spoken about……..

    The end cost factor of DDT is very high, in US$, psychological, residue disposal, when compared to many numerous Pyethroids, why?

    Firstly it takes ten times the amount of DDT to cover 1 square metre surface area as a pyrethroid such as Lambda Cyhalothrin.
    So if a pyrethroid costs per single sachet 62,5g and a 675g of DDT sold at a similar price, which they now are, what is then not taken into account is as follows:-

    100,000 non palletised 62,5g pyrethroid sachets fit into one 20foot container.  If DDT is to cover the same sq metres it states clearly that ten containers are required to transport enough DDT to do the same job.

    The price comparison is product price divided by application rate i.e. DDT price $3.98 per dose in 10 lt water at 2 gms per square mt will cover 40 sq mt = US$ 0.995 cent per square mt

    Lambda Cyhalothrin @3.98 per dose in 10 lt water @25milligrams per square mt will cover 400 square mt

    So 1 ton of Lambda Cyhalothrin. =  10 tons DDT in application rate

    The DDT carbon footprint alone is huge when one considers countries such as Mozambique ordering up to 23 containers of a pyrethroid a year and if DDT, 230 containers.

    That means in countries which have very poor infrastructure or smaller transport way with all with which to distribute; they are given a distribution headache of massive proportions.  In areas where motor bikes are used to get to inaccessible areas, they would need to make hundreds of unnecessary trips because DDT was the preferred insecticide option, ½ tonne pickups would need to be 5 tonne trucks and so the mounting costs carry on. Fuel, large vehicle fleets, additional manpower; all on roads which are most of the time problematic.

    The argument that DDT lasts twice as long is probably quite accurate, but unnecessary in most parts of sub-Sahara Africa as the dry seasons are invariably cold and relatively mosquito free.  Even so the use of many good alternatives to DDT still makes for financial and environmentally / ecologically friendly sense. The Stockholm Convention makes it clear the disposal of the residue must be undertaken in a particular manner.

    Most of the countries receiving DDT do not have the correct incinerator in place. Are these poor countries actually disposing of the waste in the manner proscribed in the Stockholm Convention or recklessly burning / burying? Another high cost factor against DDT. So who pays the transport costs to ship it to a country that has the correct disposal means? Another DDT hidden cost?

    The health issue is not a clinical “It does harm, yes” or “No it does not”. The facts on the ground are as follows.

    Much delivered DDT has not been used in IRS use. It lies for years for reasons as follows:-  The operators refuse to handle it.  They are aware of the claim that their manhood in the sperm count may be impaired. That DDT is generally regarded in the West as a serious health issue and still banned more or less universally.
    Local chiefs often refuse to let their villages be sprayed with any product let alone DDT. This because of the past bad publicity concerning large scale DDT spraying often resulting in persuasion on the ground in the use of a perfectly safe pyrethroid often takes weeks, which shows the scale of the DDT “fear factor”.

    It has become more and more prevalent for governments / NGO’s USaid etc, in Africa to force upon the local population DDT without consideration of the personal concerns of their rural people, which brings up the subject of “Human Rights”.

    Is there a case for DDT to be forced upon a population that does not want it in their living space? Is the DDT case diminished if there are perfectly good and numerous alternatives? Is it not the right of every human being to go to bed at night without anxiety and worry, whether DDTs poor publicity is ill founded or not?

    Is it not the case that a pregnant woman carrying her child for nine months has the given human right to carry that child without fear and anxiety in worrying whether the child will be deformed or have any health risks due to the enforced use in her village of spraying DDT.  In this case: The concern is not DDT but of mental health over such a prolonged period of time maybe impacting on the baby, or worse if it created a miscarriage.

              Nigel Frazer-Evans
            .(JavaScript must be enabled to view this email address)

  • Daniel Nylin Nilsson on 15th July 2010:

    Richard: I have somehow defended the traditional arguments agaist DDT from environmentalist. I think it is fair to sum them up as follows:

    1. DDT is a major threat to biodiversity
    2. DDT is a threat to human health
    3. Mosquitos develop resistance against DDT, and this is the reason that DDT use dropped in the seventies
    4. Mosquitos will eventually develop resistance against any pesticide, so pesticides can be no solution.

    I know you don’t agree with this, so let us not discuss them. What I want to say is something different.

    Nigel mentions a range of other arguments like:

    1. DDT is inefficient, and expensive
    2. Countries do not have the infrastructure to make good use of DDT
    3. DDT is politically controversial

    These arguments are fundamentally different - as you hint at yourself I don’t think that any environmentalist would see pyrethroids as the solution.

    But it seems to me you pretty much deal with Nigel’s answer as you would deal with an environmentalist’s answert: “No matter how one wants to justify an anti-DDT position (as expressed by Nigel), it still comes down to anti-insecticide groups wanting to deprive countries their right to use one of our few tools against malaria.”

    I can not find where you answer to Nigels statements. For example you write: “Resistance to insecticides is a very real and very pressing problem in many parts of Africa.  How does it help that pyrethroids are transported in smaller volumes if the insecticide itself doesn’t function to protect people from malaria?” To say that pyrethroids won’t work is not an answer to Nigels statement that many countries in Africa lack the infrastructure to make us of DDT.

  • Bart Knols on 15th July 2010:

    Time to sum up the issue raised by Nigel.

    He argues that more is needed when using DDT (this cannot be doubted, it’s a fact). Based on this he argues that shipping costs will be higher (true, hard to argue against), then he adds the carbon footprint issue (in essence true also).

    Beyond the counter statements made by Richard, I would argue that most IRS programmes in place today are outsourced to specialised agencies or contractors that will take good care of transportation and waste disposal. A good example is RTI International, which on contract from USAID executes the IRS campaigns in all the President’s Malaria Initiative (PMI) countries. The grant money made available through PMI and also other large donor agencies covers all these costs, so I don’t see the issue here (and must agree with Richard that the carbon footprint argument is over the top. If this becomes an argument, than what about global trade of agricultural produce etc.?)

    Richard’s argument ref pyrethroid resistance is based on the published facts that resistance is present on a large scale, notably but not exclusively in West Africa, so the argument indeed becomes simple: why ship something that doesn’t work but at lower shipping costs? That doesn’t make sense.

    That there is house-owner resistance to spraying (not only against DDT but in general) is well-known, but is not an issue specific for DDT. This is a generic issue that needs to be addressed but does not fit in a discussion on the pros and cons of DDT I would say.

    @Daniel - your summing up of your opinion is very interesting. Some 75 comments under this blog still makes you persist with your original opinions. I had hoped that the discussion here would have at least raised some doubt on your end that the ideas you had before might not be 100% correct. This shows how difficult the DDT issue really is: there is a pro and a con camp, and it is very hard for people to change opinions.

    Based on ‘The excellent powder’ and the discussion here I must confess that my earlier understanding of DDT was completely blurred by the stories I got at college, that I was not fully informed about this matter, and that my opinion ‘No to DDT’ was not based on the science behind this chemical. Although (like Don and Richard) I am a strong advocate to seek alternatives for DDT, I also believe (now) that the chemical will have to play a (major) role until the time that we have such alternatives.

    @Graham. Thanks (also for sending me your review of Robert’s book). Waste disposal of insecticides may be one issue, but pyrethroids on nets that are torn and discarded is another major issue. WHO actually put out a tender earlier this year for people to come up with good ideas to dispose of old nets. With millions of nets finding their way into Africa, huge amounts of pyrethroids can end up in the environment, which is particularly disastrous for fish and crustaceans…

  • Daniel Nylin Nilsson on 15th July 2010:

    A small correction wink I didn’t want to sum up my personal opinion, but the opinion prevailing among environmentalists and DDT sceptics.

  • Bart Knols on 16th July 2010:

    @Daniel - OK, thanks, sorry for my misinterpretation of your comment.

    But now that you have read all this, seen all the arguments, what is your personal opinion? Has it changed? Which arguments still hold, which ones have changed? I’m curious…

  • Daniel Nylin Nilsson on 16th July 2010:

    I have to read the book to answer that smile

    But well, I don’t think of DDT as a poison any more. There are obviosly certain risks coming with its use, but in a situation where you must choose between malaria and DDT, you have to take some risks maybe. But very much of it depends on the issues of repellancy and resistant mosquitos - after a given time the downsides must outweigh the upsides, as with any medicine.

    Moreover, I think this discussion shows that there is too much focus on DDT, as compared to other substances and other methods of fighting malaria.

  • Bart Knols on 16th July 2010:

    @Daniel - true, have a go at the book first.

    Indeed, the repellency issue is a very important one. The fact that Roberts et al list 12 pages of studies to demonstrate that the prime mode of action of DDT is repellency, is a critical issue.

    There is not too much focus on DDT - perhaps that has been the impression you got here. In other forums (for instance on MalariaWorld) we have people questioning the use of pyrethroids for IRS, or the sense of sending pyrethroid-treated nets to areas where we know resistance to pyrethroids is rampant. Such discussions are good, like the one here…

  • Daniel Nylin Nilsson on 16th July 2010:

    I am sure that people on MalariaWorld are very aware about variuos methods to deal wiht malaria. But I think that the discussion in minstream media is still very much for or against DDT.

    Whereas a goggle search for malaria and DDT gives 246 000 hits, from all kinds of sources, malaria and pyrethroids give 51 700 hits, that seem to be from more focused sources like malariajournal, etc.

    I think also, that if you assk people in the stret what chemicals can be used against malaria, very few will come up with a name different than DDT.

  • Bart Knols on 16th July 2010:

    @Daniel - it is true that such issues are discussed amongst professionals, which is a good thing. They are the ones advising policy-making entities about the pros and cons of chemicals for malaria control.

    Google hits: this shows again how politicised the whole DDT issue really is. Journalists prefer arguing for or against DDT, and don’t often know the alternatives.

    Asking people in the street normally yields nothing, not even DDT… most people in ‘developed’ countries don’t even seem to know what malaria is… see:

  • Bart Knols on 10th August 2010:


    After all, in your own South Africa it was the shift from DDT to pyrethroids and the resistance (in Anopheles funestus) that followed (to pyrethroids) that led to the epidemic in 1999. Only after DDT was used again did numbers of cases drop to very low levels again.

    So mosquito control in this case clearly failed because of resistance and only became successful when DDT came back in - in South Africa…

  • Bart Knols on 05th October 2010:

    @Klight, @Bev. Thanks for keeping the debate on DDT alive. I have not seen the documentary, where do I get it?

  • Bart Knols on 07th October 2010:

    @Commonsense - the only class of insecticides currently available for indoor residual spraying or bednet treatment are the synthetic pyrethroids. These are more costly than DDT though. The problem with pyrethroids is that in many places resistance is popping up.

    Having said that, pyrethroid-treated nets are having a big impact on malaria at the moment. It was recently estimated that over the last decade some 750,000 lives were saved as a result of using interventions like this, so the impact is there. However, it is not enough to eliminate malaria altogether… so we’re stuck and in need of additional tools (like larviciding).

    @Donald- thanks, looking forward to it.

  • Bart Knols on 10th October 2010:

    @Commonsense - well, your statement ‘why such an effective, safe chemical is not being used right now to stop..’ is not correct. DDT is firmly back on the agenda of malaria control programmes in at least 17 African countries. It is estimated that between 4-5 million kg are sprayed annually.

    The Brazil example you give is telling, though care should be taken not to exclusively attribute these events to the withdrawal of DDT. This may have played a major role, but not the only one…

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