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DDT and health, was Re: Wildavsky's "Milk Room" analog
The problem with DDT is that it is a persistant organic pollutant. The alternative preferred insecticides include Bt (B. thuriengensis) and malathion.
 
DDT was used as an adulticide meaning that it has no effect on the larvae (wigglers). DDT and it's metabolites are persistant in organisms and the environment. It is stored in fats (eg, adipose tissue) primarily as a metabolite (DDE, et cetera) and accumulates in organisms and concentrates up the food chain.
 
The advantage of using malathion as a adulticide - which is an organophosphate - is due to it's rapid rate of degradation (in most cases). The disadvantage of malathion is that it is more expensive to produce than is DDT. One other disadvantage  is the relatively high acute toxicity of malathion to humans.
 
Bt is used as a larvacide, and has relatively low toxicity to most organisms when compared to both malathion and DDT. The use of DDT in controlling mosquitoes has one application which is - in a sense - preferrable to the use of malathion, and that is in the household. The application of DDT to outdoors areas does not work very well since many mosquitoes have now developed a resistance to the DDT. In fact in the Central American nations where DDT is used to control cottonboll weevils for instance, the applications must be made frequently, up to 10 applications per crop. That amount of insecticide use results in a complete eradication of other insects, so that the agro-ecosystem becomes dependent on further use of insecticides.
 
In Ceylon it was the application of industrial scale agriculture which caused widespread malaria infestations. Traditionally the rice crops are fed with 'sediment laden' irrigation waters which prevents the malaria mosquito larvae from surviving. In addition there were many native insectivorous species of fish which also controlled the larvae of the malaria vectors. After the introduction of modern pesticides all but the most coarse fish species were extirpated, and the use of 'sediment laden' irrigation water - a natual form of mosquito control - was disrupted.  With the use of modern fertilizers there thus is not need to utilize water to raise nitrogen fixing algae, nor is there any need to intercrop with nitrogen fixing dry land grains or crops.
 
The best practice of controlling the malaria mosquito was the 3 thousand year old tradition of growing rice on the irrigated terraces which reduced the amount of habitat and increased the number of natural predators of the larvae. Now with modern agriculture methods using synthetic pesticides, there are not viable control methods. DDT will not work for more than about 10-20 years due to resistance of the adults to the organochlorine insecticide.
 
However compared to malathion, DDT is suitable as an indoor insecticide since the malaria mosquito only bites at night and it is not possible to spray malathion in a house and stay healthy or sane. The best alternative is to practice habitat abatement, and use mosquito nets.
 
Traditional agriculture use of the muddy irrigation water, insectivorous fish, and moquito nets (there are lots of other bugs that can bite too) is the best method.
 
Of course there are instances where human use of ecosystems *should* not be pursued, areas where there are high rates of malaria (eg. large tropical estuaries like the Ganges Delta, et cetera). Just like the situation where there are high concentrations of Grizzly bears (eg. some rainforest valleys where salmon spawn).
 
Areas where there are extensive dry seasons have low natural rates of malaria. For instance all of Peru excluding the Amazon rainforest lacks malaria, and yellow fever.
 
chao
 
john foster
----- Original Message -----
From: [log in to unmask]>Steven Bissell
To: [log in to unmask]>[log in to unmask]
Sent: Sunday, December 16, 2001 8:31 AM
Subject: Re: DDT and health, was Re: Wildavsky's "Milk Room" analogy

Well, I don't know, but my suspicion is that the DDT in Ceylon was *not* to control mosquitoes, but for agricultural control. I wonder if there is *any* control of mosquitoes going on. I went to school at the University of Utah in the late Pliocene. At that time U of U was the largest mosquitoes abatement research center in the world. I took classes from several mosquito guys and the rising resistance to DDT was well known. They had worked out lots of alternate methods of control, including some really clever methods of interrupting breeding cycles. If you know of any study where DDT was used *exclusively* for mosquito control, it would be interesting to see the figures. I know that the suggested application rates of DDT for mosquitoes is fairly low as compared to application rates for agricultural pests. BTW, containers of DDT use to advise applying directly to the skin of sleeping bats in order to kill them. Even the DDT folks knew, or seemed to know, that it was toxic to mammals.
 
In case you wonder the reason U of U was a mosquito center is because of the marshes around Great Salt Lake. In the summer the mosquitoes can actually dim the sun if they are swarming.
 
Steven
 

We inhabit a world of dismal success
and heroic failure.
                      Irving Horowitz
                      The Anarchists

-----Original Message-----
From: Discussion forum for environmental ethics. [mailto:[log in to unmask]]On Behalf Of Jim Tantillo
Sent: Saturday, December 15, 2001 8:01 PM
To: [log in to unmask]
Subject: DDT and health, was Re: Wildavsky's "Milk Room" analogy

Steve B. said something the other day that I've been thinking about:

 
SB: Mostly I agree, but comparing *benefits* to *costs* is an ethical judgment and Wildavsky doesn't treat it that way. I'm a bit surprised you raise this point. As an ethicist you're familiar with all the examples of how regardless of the benefits, some types of behavior are unacceptable. As in Strom Thurmond saying that Africans were better off as slaves in the south than free in Africa; wrong! The real issue is whether or not the risks of, say DDT, can be ethically compared to the benefits. Keep in mind that the *primary* reason for the use of DDT was not to eliminate human disease, it was to increase agricultural outputs. Feed the hungry? Sure, but also to make profits for agricultural producers. I've never seen a break down on the *exact* amount of DDT which was used to eliminate human disease out of the total amount used. Somehow I get the feeling the b/c ratio would not be so good on that one.

Elizabeth Whelan reports in her book Toxic Terror the following statistics (p. 101, cite below) about the incidence of malaria in Ceylon in the DDT period and after they stopped spraying DDT:

Year  /  Malaria cases reported in Ceylon  /  Comment

1948    2,800,000       No DDT
1962    31              large-scale DDT program
1963    17              large-scale DDT program
1964    150             Spraying stopped
1965    308            
1966    499
1967    3,466
1968    16,493          (January only)
1968    42,161          (February only)
1968    1,000,000      
1969    2,500,000

Whelan attributes the rise in malaria cases directly to the influence of Silent Spring and the move to ban DDT in the U.S.  Let's assume for the sake of argument that these numbers are accurate.  Was the environmental benefit worth the human cost in disease?  I don't know.  I doubt it.

Similarly, Aynsley Kellow reports in his book, International Toxic Risk Management :  "There are serious dangers in trying to reduce risk assessment of chemicals to toxicological science.  One example is the EPA risk assessment for chlorinated water in Peru.  Chlorine in the water supply is known, with a reasonable degree of certainty, to cause an elevated incidence of bladder cancer.  Peruvian officials decided to follow the lead of the US EPA and not chlorinate the water in many wells.  In an ensuing cholera epidemic more than 3500 people were saved from bladder cancer by an early death" (Kellow, p. 7; citing Christopher Anderson, "Cholera Epidemic Traced to Risk Miscalculation", Nature 354 (1991), p. 255).

What are we to make of such incidents?  I'm not sure.  One of the things Wildavsky, Whelan, and others repeat, however, is that generally there are very few *demonstrable* public health benefits that come out of the move to ban trace amounts of toxic substances in non-occupational settings.  There are very real risks involved in banning such chemicals, and sometimes the chain of causation is far clearer going the opposite way--i.e. following (some) chemical bans, the actual incidence of disease and death rises directly.

Jim T.

Kellow, Aynsley. International Toxic Risk Management: Ideals, Interests and Implementation. New York: Cambridge University Press, 1999.
Whelan, Elizabeth M. Toxic Terror: The Truth Behind the Cancer Scares. 2d. ed. Buffalo, NY: Prometheus Books, 1993.