Pesticides are one of the few kinds of chemicals specially designed to kill living things that we intentionally put into our environment in high volume. A large class of pesticides are the organophosphates (OPs), agents that affect the normal process of nerve impulse transmission.
What we call pests are one kind of organism they can kill, but OPs are unaware of our human categories like "pest." They are also adept at killing and sickening other organisms. Like us. They do it frighteningly often in the developing world, and they do it in the developed world as well. There is a nice Jack Woodall column in The Scientist about a new biotech solution to OP pesticide poisoning using genetic engineering to produce butyrylcholinesterase (BChE), a natural protein that counteracts the effects of these nerve poisons. The natural BChE only exists in microgram amounts in the blood. The new biotech method can produce it in kilogram quantities. Ready Woodall's account for more details on the BChE effort. But his brief review of the public health problem of OP poisoning is worth a pull quote:
Despite using only 25% of the world's pesticides, developing countries are home to 99% of pesticide-related deaths.
In the year 2000, hospitals in six Turkish cities were flooded by 2,000 students with poisoning symptoms after eating hazelnuts. Fortunately, nobody died. The nuts had been stored for a long time in a grain depot disinfected with an organophosphate (OP) pesticide.
The problem of pesticide poisoning is most acute in developing countries, where workers mix OP pesticides and spray fields without using gloves, goggles, or protective clothing, and then enter sprayed areas without waiting a safe interval. Despite using only 25% of the world's pesticides, these countries are home to 99% of pesticide-related deaths.
It's not just a problem in the developing world: In 1998 in California, all 34 workers fell ill after returning to weed a crop sprayed with an OP pesticide without waiting the recommended 48 hours. One was hospitalized. (Eating food treated with OPs is, of course, not nearly as harmful as swallowing heavily contaminated nuts or walking in newly-sprayed areas.)
A 2005 report on the International Workshop on Secure Access to Pesticides in conjunction with the Annual Congress of the International Association for Suicide Prevention, Durban, South Africa, estimated that there were 3 million cases of pesticide poisoning resulting in as many as 300,000 deaths per year, more than 100,000 of them in China. There's another risk: In rural areas, a significant percentage of people attempting suicide (up to 90%, in Malaysia) use pesticides, and close to 80% of all pesticide-related attempted suicides use OPs. This is a situation that needs some kind of a solution. Enter the military. (Jack Woodall, The Scientist)
Death and acute illness are just one of a large number of bad outcomes. For example, in South Africa empty pesticide plastic bottles are often used to carry drinking water from the stream or spring. A case control study a couple of years ago suggested that babies born to women who used plastic containers for fetching water were over six times as likely to have a baby with a birth defect.
Maybe the use of butyrylcholinesterase will be an important way to prevent pesticide poisoning. Here's another. Stop using pesticides except under the most urgent of circumstances. We shouldn't be surprised that people are being poisoned by chemicals that have been designed to be poisons. We should be surprised that they are often portrayed as harmless to humans but deadly to organisms who share much of our basic neurophysiology.
But when they're in widespread use, people shrug off the idea that they're harmful. Common, chronic dangers are evaluated as less important than unexpected ones, which is why we have the War on Terror and not the War on Excessive Speed Limits and Pesticide Usage.
One day when I was out weeding, I had some idiot neighbor spray Round-up next to me. He couldn't believe it when I became unhinged and started yelling at him! He said, "It's just Round-up." I responded with, "It's just a freakin' poison!" Argh!
Without doing a lot of literature review, I can't see how this would work, or be a substitute for existing treatments. Maybe this is just hype?
OP's work by inhibiting acetylcholinesterase at the synaptic junction. Biological monitoring is an assay for serum cholinesterase, which I think is mostly butyryl cholinesterase; < 30% inhibition from baseline is considered OK by various authorities including ACGIH. So the bioassay is an indirect indicator of what's going on at the site of action. After a career which began with OP's, I still don't know what BuChE does, but it must do something, and a whole lot of extra might do something bad.
Second, OP pesticides are thionates which have to be oxidized to inhibit AChE. In my day you couldn't find the oxygenated moiety in the blood by gas chromatography, either because it was too short lived to survive the work up or because it is generated in situ from serum borne thionates. But, the thionates aren't going to react with the BuChE.
Anyway, the notion that you could get enough BuChE into circulation quickly to scavenge or compete with AChE seems unlikely. And it seems unlikely that BuChE in circulation would get into the tissue where the bad stuff is happening.
Maybe another reader has more energy?
Frank: I got the impression that the BChE was going to be used on the food or contaminated environment but I don't know. That's one reason I didn't write more about it. too little info. But primary prevention also should be the main focus, hence the way the post was written. Your questions are good ones and I hadn't thought that hard about the BChE. Now that you call attention to it, it may be hype to raise money for investmnet.
Good topic Revere. Pandora mentioned "Roundup" which is a herbicide. Roundup contains a chemical "glyphosate" that sounds as though it might be an organophosphate, although it does not (at wikipedia) contain carbon.
In the local agricultural community, herbicides are generally considered less hazardous to handle than pesticides. In concentrated form (before dilution to 0.5% for spraying) glyphosate is an unattractive yellow syrup.
Roundup contains a chemical "glyphosate" that sounds as though it might be an organophosphate, although it does not (at wikipedia) contain carbon.
The wikipeia item on Glyphosate shows both a flat diagram and an image of a ball-and-stick model of the molecule, both of which have three carbon atoms. The IUPAC name given is sodium 2-[(hydroxy-oxido-phosphoryl)methylamino]acetic acid, which has two carbons in the acetic part and another in the methlamino part.
Thanks DD. I just saw the flat diagram, and was not aware of the shorthand convention which does not show carbon as "C".
A study from the Harvard School of Public Health suggested that there may be a link between occupational exposures to pesticides and Parkinsons disease.
"Researchers found that 1,956 farmers, ranchers or fishermen were 14 times more likely to be exposed to pesticides compared with people in other occupations. Blue-collar workers had a two-fold higher risk of exposure to pesticides.
Even after adjustment of other risk factors including age, gender and smoking status, the risk of Parkinson's still was significant among those who were exposed to pesticides, 1.7 times higher than that for those who were not exposed."
I don't think you're going to get rid of much pesticide use anywhere, but especially not in poor countries. The extra yield/decreased risk of losing your whole crop is more important when you're poor than when you're well-off, and much more important when the cost of being poor is watching your kids starve to death, than when it's the embarassment of losing your farm and going on public assistance.
albatross: IF they work and the pests aren't resistant and IF there remains a market for your tainted goods and IF the pesticides continue to be sold and IF you live long enough and don't poison yourself and IF there isn't a better and cheaper way to get the same result.
In an article by Mohamed Dalvie and Leslie London in the journal of Environmental Research in 2006 it states that pesticides and more importantly organophosphates could possibly accountn for the large number of incidence of Guillaine-Barre syndrome. A study was done that supports the idea that aerial spray of organophosphates may be causitive for the rare neurological disease known as GBS.
Dalvie, M.A., London, L. (2006). The impact of aerial application of organophosphates on the cholinesterase levels of rural residents in the Vaalharts district, Northern Cape Province, South Africa. Environmental Research, 102(3): 326-332.
Lindsay: Thanks for the link. I know the article (and in fact I know Leslie).