The myth of DDT versus the reality of malaria in Africa - Page 4 - U2 Feedback

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Old 06-26-2005, 07:31 AM   #46
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exposed as the idealist i am yet once again.


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Old 06-26-2005, 07:56 AM   #47
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Ideals are sooooo 1996

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Old 06-26-2005, 07:57 AM   #48
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Originally posted by cardosino

You lost me as soon as you said "UN".
Geez, I don't hate the UN *that* much. It's a human institution.
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Old 06-26-2005, 08:45 AM   #49
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If you would like a more scientific look at DDT try this website

Listed are 16 685 toxicology articles, 374 developmental and reproductive toxicology articles, articles on carcinogenicity and mutagenicity, environmental toxicology and the environmental fate of the chemical and metabolism in a wide range of animal species with regard to DDT.

This abstract is from the World Health Organisation.


WHO working group

Source: Environmental Health Criteria , 83 (1989) 98 p


Physical and Chemical Properties: DDT is an organochlorine insecticide which is a white crystalline solid, tasteless and almost odourless. Technical DDT, which is principally the p,p' isomer, has been formulated in almost every conceivable form. Uptake. Accumulation, and Degradation: The physicochemical properties of DDT and its metabolites enable these compounds to be taken up readily by organisms. High lipid solubility and low water solubility lead to the retention of DDT and its stable metabolites in fatty tissue. The rates of accumulation into organisms vary with the species, with the duration and concentration of exposure, and with environmental conditions (BCFs in flow-through systems; Daphnia = 114 000, fish = 8500-154 000). The high retention of DDT metabolites means that toxic effects can occur in organisms remote in time and geographical area from the point of exposure. These compounds are resistant to breakdown and are readily adsorbed to sediments and soils that can act both as sinks and as long-term sources of exposure (e.g., for soil organisms). Organisms can accumulate these chemicals from the surrounding medium and from food. In aquatic organisms, uptake from the water is generally more important, whereas, in terrestrial fauna, food provides the major source. In general, organisms at higher trophic levels tend to contain more DDT-type compounds than those at lower trophic levels. Such compounds can be transported around the world in the bodies of migrant animals and in ocean and air currents. Toxicity to Microorganisms: Aquatic microorganisms are more sensitive than terrestrial ones to DDT. An environmental exposure concentration of 0.1 ug/litre can cause inhibition of growth and photosynthesis in green algae. Repeated applications of DDT can lead to the development of tolerance in some microorganisms. There is no information concerning the effects on species composition of microorganism communities. Therefore, it is difficult to extrapolate the relevance of single-culture studies to aquatic or terrestrial ecosystems. However, since microorganisms are basic in food chains, adverse effects on their populations would influence ecosystems. Thus, DDT and its metabolites should be regarded as a major environmental hazard. Toxicity to Aquatic Invertebrates: Both the acute and long-term toxicities of DDT vary between species of aquatic invertebrates. Early developmental stages are. more sensitive than adults to DDT. Long-term effects occur after exposure to concentrations ten to a hundred times lower than those causing short-term effects. DDT is highly toxic, in acute exposure, to aquatic invertebrates at concentrations as low as 0.3 ug/litre (Daphnia, 48-h LC50 = 0,5-4.7 ug/l (static tests)). Toxic effects include impairment of reproduction and development, cardiovascular modifications, and neurological changes. Daphnia reproduction is adversely affected by DDT at 0.5 ug/litre. The influence of environmental variables (such as temperature, water hardness, etc.) is documented but the mechanism is not fully understood. In contrast to the data on DDT, there is little information on the metabolites DDE or TDE. The reversibility of some effects, once exposure ceases, and the development of resistance have been reported. Toxicity to Fish: DDT is highly toxic to fish; the 96-h LC50s reported (static tests) range from 1.5 to 56 ug/litre (for largemouth bass and guppy, respectively). Smaller fish are more susceptible than larger ones of the same species. An increase in temperature decreases the toxicity of DDT to fish. The behaviour of fish is influenced by DDT. Goldfish exposed to 1 ug/litre exhibit hyperactivity. Changes in the feeding of young fish are caused by DDT levels commonly found in nature, and effects on temperature preference have been reported. Residue levels of > 2.4 mg/kg in eggs of the winter flounder result in abnormal embryos in the laboratory, and comparable residue levels have been found to relate to the death of lake trout fry in the wild. Cellular respiration may be the main toxic target of DDT since there are reports of effects on ATPase. The toxicity of TDE and DDE has been less studied than that of DDT. However, the data available on rainbow trout and bluegill sunfish show that TDE and DDE are both less toxic than DDT. Toxicity to Amphibians: The toxicity of DDT and its metabolites to amphibians varies from species to species; although only a few data are available, amphibian larvae seem to be more sensitive than adults to DDT. TDE seems to be more toxic than DDT to amphibians, but there are no data available for DDE. All the studies reported have been static tests and, therefore, results should be treated with caution. Toxicity to Terrestrial Invertebrates: There have been few reports on the effects of DDT and its metabolites on non-target terrestrial invertebrates. Earthworms are insensitive to the acutely toxic effects of these compounds at levels higher than those likely to be found in the environment. The uptake of DDT by earthworms is related to the concentrations in soil and to the activity of the worms; seasonally greater activity increases uptake. Thus, although earthworms are unlikely to be seriously affected by DDT, they pose a major hazard to predators because of the residues they can tolerate. Both DDT and DDE are classified as being relatively non-toxic to honey bees, with a topical LD60 of 27 ug/bee. There are no reports on laboratory studies using DDE or TDE, in spite of the fact that these are major contaminants of soil. Toxicity to Birds: DDT have moderate to low toxicity to birds when given as an acute oral dose (LD50 = 600 - > 4000) or in the diet (5-day LC50 = 300-900). DDT and its metabolites can lower the reproductive rate of birds by causing eggshell thinning (which leads to egg breakage) and by causing embryo deaths. However, different groups of birds vary greatly in their sensitivity to these chemicals; predatory birds are extremely sensitive and, in the wild, often show marked shell thinning, whilst gallinaceous birds are relatively insensitive. Because of the difficulties of breeding birds of prey in captivity, most of the experimental work has been done with insensitive species, which have often shown little or no shell thinning. The few studies on more sensitive species have shown shell thinning at levels similar to those found in the wild. The lowest dietary concentration of DDT reported to cause shell thinning experimentally was 0.6 mg/kg for the black duck. The mechanism of shell thinning is not fully understood. Toxicity to non-laboratory Mammals: Experimental work suggests that some species, notably bats, may have been affected by DDT and its metabolites. Species which show marked seasonal cycles in fat content are most vulnerable, but few experimental studies on such species have been made. In contrast to the situation in birds, where the main effect of DDT is on reproduction, the main known effect in mammals is to increase the mortality of migrating adults. The lowest acute dose which kills American big brown bats is 20 mg/kg. Bats collected from the wild (and containing residues of DDE in fat) die after experimental starvation, which simulates loss of fat during migration.

The major issues with DDT are:

1. It bioaccumulates, ie it builds up in the fatty tissue of animals along the food chain.
2. It does not readily break down, so exists for a long time in the soil/water or whereever it is found.
3. It has been shown to be a possible human carcinogen at low levels of exposure.
4. It has reproductive impacts.

I think that the negatives out weigh the positives and I am sure there are other much more suitable alternatives.
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Old 06-27-2005, 09:55 PM   #50
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I wish I recalled the links I found the other night...a series of independent research articles I'll try to dig up. I'd add to tania's list that it has been linked pretty strongly (the suspected mechanism is DDT's estrogenic properties) to reduced period of lactation and also to low-birthweight babies. Both of those can be considerable risks to developing nations fighting battles against hunger and other diseases.
There are also some DDT-resistant breeds of mosquitoes...
I think it would be silly not to look at the relative risks in deciding whether DDT should be used in limited ways to destroy mosquitoes, but other means should be researched and continued and its use should be seriously monitored and limited so that it doesn't get widespread in the environment.

Good to see the conservatives worried about malaria, better if they then got together with actual experts in these issues to work out the best way to go and not just slam environmental protection groups or cry end-all-regulatory-protection with every possible fibre of their public beings...

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Old 07-06-2005, 09:05 PM   #51
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This link take you to the World Health Organisation recommendations for insecticidal treatments to control mosquitoes.

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