Anthonares

Chapters 4 and 5 of Tom Bethell’s “Politically Incorrect Guide to Science” follow a pair of worthwhile reads on Nuclear Power and Radiation’s low-dose effects, and I had high hopes that Bethell would stick to the focused arguments of chapters 2 and 3. I was happy, then, to see that each of the chapters 4 and 5 addressed only one topic: Dioxin and DDT, respectively. I am going to do little more than summarize the chapter on Dioxin mainly because I have absolutely no prior knowledge here, and I have no time to research it. I will respond to the chapter on DDT, however, because of two reasons: 1) Bethell drastically misstates the science on DDT’s harmfulness to ecosystems, and 2) he makes an excellent point that the debate about banning DDT did not acknowledge appropriately its usefulness in preventing malaria, and thus banning the substance has resulted in millions of human deaths.

Update 21 December 2005:Several readers have either commented or written to me about the gross misrepresentation of the DDT case in Bethell’s book. I did not even consider mosquito resistance of DDT due to the blanket spraying techniques used in the 1950s and 1960s (which develops resistance due to hormesis, a favorite idea of Bethell’s). Thus, the application of DDT in that fashion would have, in fact, led to the deaths of millions if the DDT-resistant mosquito strains had spread widely throughout Africa. Largely, today, DDT is used in high-risk areas and inside of homes, limiting the potential for creating DDT-resistant mosquitos. Thus, yet again, Bethell has demonstrated his dishonest presentation of nearly every issue in his book. Please take this information into consideration when reading the rest of this chapter review.

Summary of Bethell’s Points:
Chapter 4: Dioxin
This chapter begins with a multi-page discussion about chemical hormesis (aka the dose-response curve, as previously mentioned) in order to argue that, in small doses, dioxin is probably beneficial like almost every other chemical compound. He then lists a selected series of dioxin releases as anecdotal evidence of its harmlessness. Next, he points to the lack of definitively diagnosable dioxin-related health effects in most Vietnam soldiers, though he does not mention the possible cases within the group who had the most intimate contact with Agent Orange “Operation Ranch Hand.” Finally, he moves on the the assertion that dioxin is carcinogenic, pointing out that there is no real evidence linking dioxin to human cancer, but to liver cancer in rats.

Chapter 5: DDT
Bethell begins his chapter on DDT by providing a bit of its history, noting that it was used safely by humans for a long time until Rachel Carson released her landmark environmental work Silent Spring. In a brief (and surprisingly gentle, for a subsection entitled “Silent But Deadly”) summary of Carson’s work, Bethell mentions how the tide was soon turned against DDT. Then, he discusses the results of studies on chickens and pheasants (though he doesn’t mention this, I had to look it up), and concludes that eggshell thinning seen in eagles and other raptors is not a result of DDT ingestion. Finally, he moves on to a thorough criticism of the effect of the DDT ban on malaria deaths, and points out that Carson’s book did not once mention the immense benefit of widespread DDT spraying to humans in malaria-prone areas.

My Response:
Keeping in mind the fact that Bethell editorializes wherever possible, throws in partisan political tripe, does not cite useful references nearly often enough, and ignores evidence that goes against his hypothesis, these two chapters remained surprisingly cogent. Chapters 6 and 7 will not see the same compliment, however, but for now, read on!

Chapter 4:
It appears, from a preliminary web search on the topic of dioxin’s toxicity that Bethell is largely correct here. Small doses do seem to pose little to no human health risk. However, as is his style, he is very selective in presenting evidence and offers nothing but vague straw-man style evidence against his hypothesis. Unfortunately for Bethell, this lack of honest presentation of the opposing position leads me to suspect that there is more to the story, even though this may not be the case. Also, he does not seem to acknowledge the process of biomagnification by which most of the dioxin found in humans enters us. Biomagnification occurs in any long-lived fat-soluble compound. The basic process is that benthic organisms (i.e. bottom-dwelling creatures) first ingest dioxin through contaminated sediment. They are consumed by larger predators, who are then consumed by fish. These fish store the dioxin in their fatty deposits until they, too, are consumed by larger fish. This process continues until the fish that we eat can have greatly magnified dioxin concentrations. Then, nursing mothers pass these high concentrations to their children via fat-rich mother’s milk. Rapidly developing babies may be at the greatest risk of dioxin’s effects, and because of the effects of biomagnification, we should be extremely careful with how we regulate dioxin. Whenever there is great scientific uncertainty, but large potential for harm, it is wise to err on the side of safety.

Chapter 5:
Bethell’s arguments that DDT is not harmful to raptors’ eggs is completely wrong. It is not harmful to many other types of birds’ eggs, but not all birds are physiologically distinct. The decrease in background DDT is largely considered to be the reason why so many raptors are on the rebound. Also, though he does not discuss it (again, extremely selective use of scientific evidence) DDT is a broad-spectrum pesticide that fundamentally disrupts the larval stages of developing insects. It is the mass extermination of many types of insects that is responsible for the “Silent Spring” in Carson’s book. Thus, DDT breaks one of the bottom-most links in the intricate chains of many ecosystems.

Now, throwing out Bethell’s science entirely, his discussion of the DDT ban is still extremely germane. DDT helped to wipe out malaria in the US and most of Europe, and its widespread use in Africa undoubtedly saved millions of lives each year. Thus, banning it without thought to the consequences on malaria-prone peoples was extremely irresponsible. A thoughtful and honest discussion must take place: how can we use DDT (currently the most effective means of preventing malaria) carefully so as to avoid destroying entire ecosystems yet save the lives of millions? Removing the politics from DDT and focusing on the science will provide the best forum for this discussion. Note, many African countries have resumed DDT spraying in the worst-affected areas, so this discussion had best take place soon.