DDT…a bit of pesticide history

Briefly talking about genetically modified corn in my last article got me thinking about the pesticide issue and why I believe so strongly in organic food.  It’s frightening to think how the mistakes of the past will continue to so adversely affect future generations.  This is why I wanted to look into the past to find out what has taken place.  I don’t like what I found and have found myself saddened by this information.  If only we had realized how much every living thing is connected we may not have made such a huge mistake.  Here’s what I found:In 1939 Swiss chemist Paul Muller discovered the first widely used, synthetically created pesticide.  It was dichlorodiphenyltrichloroethane or DDT.   Until the 1960’s it was considered a miracle because:

    It was toxic to wide range of insect pests, but seemed to have low toxicity to mammals.

    It didn’t break down quickly in the environment, so it didn’t have to be reapplied often.

    It was not water-soluble, it was persistent, so didn’t get washed off by rains.    It was inexpensive and easy to applyFor his discovery, in 1948, Muller was awarded a Nobel Prize.  Inexpensively killing pests to boost crop yields caught on like a wild fire that spread all over the planet.  We even began using it for non-agricultural reasons as well.  In WWII soldiers were deloused with it.  Mosquitoes were controlled in residential areas in the US bringing malaria under control (unfortunately it is on the increase now as these insects have developed a resistance to chemical pesticides) In 1962 a marine biologist named Rachel Carson brought the environmental problems caused by synthetic pesticides to the attention of the American public in her best selling book Silent Spring.  She focused on the chlorinated hydrocarbons, such as DDT, and pointed to evidence linking them to death of non-target creatures, such as birds. She argued that the death of these non-targets occurred via two basic ways:

(1) Direct toxicity. It was discovered that DDT was toxic to fish (especially juveniles) and crabs, not only to insects.

(2) Indirect toxicity, related to its insolubility.

She reported that insect and worm eating birds were dying in areas where pesticides had been aerially applied.

The pesticide manufacturers claimed that the minute amounts found in the environment couldn’t possibly be killing them.  However, some experimental work demonstrated that even small amounts of some of the pesticides could affect the survival and reproduction of some species.  More important, research demonstrated that, although concentrations were very low in the soil, atmosphere and water, concentrations were higher in plants, higher still in herbivores, and still higher as one moved up the food chain.

The indirect toxicity related to two principles:

(1) Bio-concentration – the tendency for a compound to accumulate in an organism’s tissues (especially in fatty tissues for the fat soluble DDT) and

(2) Bio-magnification. – an increase in concentration up the food chain.

Because DDT was persistent, there was abundant opportunity for it to be taken up from the environment by organisms.

Thus, concentrations had increased 10 million times up this progression; largely because of bio-magnification (differential uptake and secretion may also be involved). These concentrations were not directly lethal to the highest order carnivores, but did impair their reproduction (Hmmm…I wonder if this is why we have so many reproductive problems today…aren’t we the highest level carnivores?).  DDT (actually, its breakdown product DDE) reduced the deposition of calcium in eggshells. The birds thus produced thinner shell that cracked more readily during incubation.

The populations of many predatory populations (the highest order carnivores), such as bald eagles and brown pelicans were nearly eliminated. The peregrine falcon disappeared in the eastern US as a result of reproductive failures by the 1960’s.

DDT (as DDE, a breakdown products from DDT) also appeared in the fatty tissues of seals and Eskimos, far from any area of use, indicating that, because of its persistence, it was being transported long distances in the atmosphere and then being washed away by rains. It also started showing up in human breast milk at remarkably high concentrations — so high that if it were cow’s milk, the milk couldn’t legally be sold through interstate commerce! DDE is the most widespread contaminant in human milk around the world. (This makes me sick as I nursed my child.  She has a mild form of autism like 1 in 300 children now do and it makes me wonder if this isn’t actually the cause, but that’s another topic).These same types of concerns, the accumulation of persistent organic pollutants (specifically, PCB’s and organochlorines, such as DDT) are showing up in killer whales (orcas).  Similarly, an article from August 2, 2005 in the journal, Science, indicated that concentrations of DDT and its residues are quite high in sperm whales (which are meat-eaters) across the Pacific Ocean.(While researchers used to think that DDT was not toxic to mammals, it is increasingly believed that, at high concentrations and for chronic, long-term exposures, it may be involved with liver cancers, reproductive abnormalities (e.g. ultra high levels of estrogen or low levels of adrenal steroids, such as progesterone), and other human and mammalian effects.)

These concerns and the resulting public outcry prompted the US Environmental Protection Agency (EPA) to cancel the registration of DDT in the US in 1972. (All pesticides used in the US must be registered with the federal government, so this cancellation effectively pulled DDT off of the US market.) (Its use is still allowed in special cases, as in controlling vectors of human diseases.) Manufacture of DDT in the US did continue for export until the late 1970’s. Currently there is no manufacturing of DDT in the US.

DDT is still, sadly, widely used in less developed countries.  And, again sadly, (but all too typically), when the last DDT manufacturing plant in the US was dismantled in 1983, it was sold to Indonesia, where it is currently manufacturing DDT.

Since the time of the US ban on DDT, populations of many of these predatory birds have recovered remarkably. (However, for information suggesting that many of the pesticides used today in the US are toxic to birds, resulting in the deaths of thousands per year [perhaps even millions], even when used in the recommended way.

In December 2000, 122 nations (including the US) signed a treaty intending to phase out completely Persistent Organic Pollutants (“POP’s”)(organic…meaning containing a carbon compound), including DDT.

(Twenty five developing countries, however, got exceptions allowing them to keep using DDT, as it is the cheapest and most accessible defense against malaria-transmitting mosquitoes. This whole malaria and DDT issue is really tough — between 1 and 3 million people die each year from malaria — a death toll comparable to that resulting from AIDS. In some cases, DDT is still effective against the disease-bearing mosquitoes, and many people feel that the benefits from continuing to use it for this purpose outweigh the risks. Resistance problems seem likely, ultimately, to force a change in control approaches in any case. There is considerable success with the use of bed-nets — mosquito netting that is treated with an insecticide and suspended over a person’s bed, protecting them during the evening and night when the mosquitoes are most active — coupled with more effective dissemination of anti-malaria drugs, and measures such as filling chinks in walls that fill with water and provide mosquito breeding grounds.)

These POP’s are generally fat-soluble (as is DDT), and are also very dispersable (occur in forms that are able to travel over great distances). The list of 12 POP’s covered by the treaty includes nine pesticides (Aldrin, Chlordane, DDT, Dieldrin, Endrin, Heptachlor, Hexachlorobenzene, Mirex and Toxaphene) as well as PCB’s, furans, and dioxins. Dioxins are a by-product of some types of paper processing, and are produced in other processes as well. You may remember hearing about “agent orange” — a defoliating agent used during the Viet Nam war? It has been implicated in causing a diversity of health problems, and dioxins are causal agents for several of these problems. Dioxins aren’t part of the active ingredients of agent orange (which are 2,4,5-T and 2,4-D), but are byproducts of their production. The EPA wrote, in 1985, that dioxins are “the most potent carcinogen ever tested in laboratory animals.” Many more POP’s are likely to be added to the list of globally-banned compounds, but ecological/epidemiological studies linking them to human or ecosystem injury have not been completed.

The atmosphere is not the only means by which POP’s get moved around: Arctic seabirds and migratory fish species, such as salmon, transport these compounds from the ocean to the land. For example, many pelagic seabirds have nesting colonies near inland lakes in the Arctic (Science July 15, 2005).

Another interesting accomplishment of this treaty was acceptance of the “precautionary principle,” which reverses the traditional regulatory burden of proof. Instead of assuming that a compound is harmless unless it can be shown to be dangerous, manufacturers must avoid production of likely POP’s even if they are not actually proved to be POP’s — that is; they are assumed to be “guilty” of causing harm until they are proved to be otherwise. Another way of stating the precautionary principle is to say that, if a technology or activity may pose a threat or harm, measures to anticipate and prevent that harm are warranted. My next article will be posted sometime next week.  I will continue to look into pesticide trends and hope that I don’t find anything anymore scary.  Until then if you’d like to look into DDT a bit more, here are some links for you. http://www.orcafree.org/danger_toxins.htmlhttp://www.environmentalhealth.ca/spring03false.html

http://www.environmentalhealth.ca/spring04buildup.html

http://www.mindfully.org/Health/2005/Toxic-Breast-Milk9jan05.htm

http://www.panda.org/about_wwf/what_we_do/policy/toxics/problems/our_chemical_world/ddt/index.cfm

~ by digitalpoetry on December 29, 2007.