Saturday, March 28, 2009

DDT - The Good and the Bad

Yes, another rant on DDT. You can read my other rants here, here, here and here. What brings on the latest rant you ask? It's the debut of "A Sense of Wonder", a film about Rachel Carson, at North Country Community College in celebration of National Women's History Month.

There is some disagreement about how much responsibility Rachel Carson deserves for the drastic reduction in the use of DDT to control malaria worldwide. Carson was not opposed to using DDT to control disease. However, the reduction in the use of DDT to control disease, especially malaria, has been attributed to her book "Silent Spring".

"Silent Spring" also led to the formation of the Environmental Defense Fund an organization I generally support. Unfortunately, on the issue of the use of DDT to control malaria, I'm of the opinion that the EDF provides some vary slanted information concerning the effects of DDT in humans (although they do somewhat support the use of DDT for indoor spraying in malaria control).

Concerning a relationship between cancer and DDT the EDF writes:
Most of what we know about DDT's toxicity to humans (as with many chemicals) is derived from laboratory-animal studies, which have demonstrated that DDT is likely to cause cancers and other health problems.
EDF makes it sound like this relationship has been scientifically proven. According to the Malaria Foundation International which cites an article published in Lancet, it has not. Exotoxnet, a consortium of Cornell University, Michigan State University, Oregon State University and the University of California at Davis says
Thus it appears that DDT may have the potential to cause genotoxic effects in humans, but does not appear to be strongly mutagenic
and, concerning cancer,
no significant associations were seen between DDT exposure and disease
EDF also claims:
To attribute the resurgence in malaria to a failure to use one specific pesticide is not only misleading, it's incorrect.
There is evidence and opinion that says otherwise, this article published in PLOS for instance or this article published in Science News.

Fortunately, the WHO is promoting the indoor use of DDT to prevent malaria. You can learn much more about how DDT prevent malaria by going here.


timpanogos said...

EDF makes it sound like this relationship [DDT and cancer] has been scientifically proven.

Every cancer-fighting agency on Earth lists DDT as a "probable human carcinogen." Humans are the only mammals where DDT is not known to be a rather potent carcinogen; it's suspected of being a weak one.

How much consensus is required before you join the cancer fighters?

PCS said...

I cite "Agency for Toxic Substances and Diseases Registry (ATSDR)/US Public Health Service, Toxicological Profile for 4,4'-DDT, 4,4'-DDE, 4, 4'-DDD (Update). 1994. ATSDR. Atlanta, GA."

The available epidemiological evidence regarding DDT's carcinogenicity in humans, when taken as a whole, does not suggest that DDT and its metabolites are carcinogenic in humans at likely dose levels (from Extoxnet)

From the 11th Report on Carcinogens

There is inadequate evidence for the carcinogenicity of DDT in humans (IARC 1974, 1987, 1991). Epidemiological studies are available on the cancer risks associated with exposure to DDT; however, due to exposure to multiple pesticides and the small size of the study groups, it is not possible to draw definitive conclusions from these studies (IARC 1991).

There will be concensus when the evidence supports DDT exposure causing cancer in humans.

The children dying of malaria do not live long enough to die from cancer.

timpanogos said...

I'll defer to the cancer experts. By 1994, no, DDT probably wasn't known as a carcinogen as it is now -- the role of estrogen in causing cancer wasn't firm (DDE, the first daughter of DDT, mimics estrogen). DDT is a weak carcinogen. And while it could probably be used safely were that its only health issue, there are many other reasons not to use it.

DDT is toxic to beneficial wildlife. It kills the predators of mosquitoes much more effectively than it kills mosquitoes. It's not as effective as other pesticides, and it wreaks havoc on ecosystems.

DDT use by the World Health Organization was suspended in Africa in the mid 1960s because it ceased to work. Overuse of the stuff in agriculture had bred mosquitoes that were immune to DDT, or at a minimum, highly resistant to it. So the dream of knocking down mosquitoes for six months or a year until malaria could be wiped out in humans, was defeated.

Recent studies show that the toxic effects of DDT, including killing off the food fish for Africans, far outweigh the benefits of broadcast spraying, and in the end cause more acute deaths than those who might be spared malaria by the stuff. DDT is no panacea.

Kids with malaria would love to be rid of it. DDT can't do that. Only good pharmaceuticals can do that, delivered effectively in a working health care system. Those things cost money, and DDT can't help there, either.

The war against malaria requires the use of many weapons. DDT could be one, but it can't be the only. Hoping to embarrass Rachel Carson, a dead scientist who was right, doesn't save anyone.

PCS said...

We must be reading completely different literature. I find little substantial evidence that DDT exposure, especially that used in malaria control, results in any cancer. Not surprising since DDT hasn't been used in decades. The animal data is also equivical. Maybe you can provide some links for me. I'm spent enough time looking for evidence that supports DDT exposure and cancer in humans.

PCS said...

BTW, as you well know, the effects of DDT on wildlife and the environment was due to agricultural use of the pesticide, not indoor spraying.