Environment

Pesticides and Cognitive Development

Chemical Institute of Canada — Mon, 25 Apr 2011 01:59:14 GMT

The womb is a factory. It is here that chemicals are assembled into a living machine of incredible complexity called a baby. Where do these chemicals come from? Mommy! She eats and she drinks. She processes the proteins, fats, carbs, minerals and vitamins she ingests to provide the building blocks needed by the growing embryo. But what if a monkey wrench gets thrown into the machinery at this point? What if chemicals not needed for healthy development find their way into the uterus? Can they gum up the works, possibly producing long term consequences? No doubt.

Agents that can disturb the development of the embryo or fetus are called teratogens. They may cause outright birth defects, as in the case of thalidomide, alcohol or the acne treatment isotretinoin. Or a teratogenic effect may not appear until years later. Diethylstilbesterol (DES) was used to treat recurrent miscarriage in the 1950s and 60s and was eventually found to cause a rare type of vaginal cancer in the daughters of women who had been treated in the first trimester of pregnancy. But more subtle effects are also possible. Lead and mercury exposure for example have been linked with problems in cognitive development. And there has also been suspicion that in-utero exposure to certain pesticides may impair intelligence later in life. That may not be as harebrained as it sounds.

A number of recent studies have explored the possibility of a such an effect by administering various intelligence tests to children whose mothers’ exposure to organophosphate pesticides during pregnancy had been determined by analysis of either umbilical cord blood or urine samples. Organophosphates are a common family of pesticides and function by inhibiting the action of an enzyme that breaks down the neurotransmitter acetylcholine. Essentially, these chemicals kill pests by over stimulating their nervous system. Since human nerves also use acetylcholine as a neurotransmitter, organophosphates can also affect us. Indeed, the classic chemical warfare agents such as Sarin are organophosphates and of course these can kill. Exposure of a developing embryo to tiny amounts of organophosphates is not going to be lethal, but what about subtle effects? Recent studies suggest a decided possibility.

In one study, urine from pregnant women in a farming community was collected and analyzed for organophosphate content. The same was done for their children at 6 months of age, as well as at 1, 2, 3.5 and 5 years. When the kids turned seven, intelligence tests were administered. The higher the pesticide level in the mother’s urine, the worse the offspring performed in terms of working memory, processing speed, verbal comprehension, perceptual reasoning and IQ! The differences were not huge, but statistically significant. Remarkably, there was no correlation of cognitive problems with pesticides in the childrens’ urine, suggesting that the critical period of exposure is in utero.

Another study examined the effects of chlorpyrifos, an organophosphate, on inner-city children whose mothers were exposed mostly through residential pesticide application. Levels of the chemical were measured in umbilical cord blood and again intelligence tests were performed at seven years of age. Again there were small declines in IQ and working memory with an increase in chlorpyrifos in umbilical blood. Yet a third study examined prenatal maternal blood for organophosphates as well as for the presence of paraoxonase, a key enzyme in the metabolism of organophosphates. In this case too, cognitive development was affected in parallel to increased blood levels of organophosphates, and furthermore, there was a genetic involvement. Children of mothers who carried a gene that imparts slow activity to the enzyme that helps break down organophosphate were more affected.

These are interesting studies, but there are a few items to note. Organophosphate use is declining and has been virtually eliminated from all but agricultural use. Chlorpyrifos is not allowed in products formulated for residential use. Also such studies can show an association but cannot prove cause and effect. Could other factors have been involved? Alcohol? Smoking? Nutritional differences? Mercury or lead exposure? Still, the fact that measures of intelligence were linked to levels of pesticides in maternal urine or umbilical blood in a proportional fashion is very suggestive of these chemicals being the culprits.

The take-home message here is that we have to be careful with the use of pesticides, particularly in terms of exposure during pregnancy. After all, let’s face it, pesticides are designed to do harm. What, though, can an individual do to reduce the risk? When pregnant, application of pesticides at home should be avoided. What about eating organic produce? Pesticide residues on conventional produce occur only in trace amounts, but there is some exposure. If an argument is to be made for buying organic, it is probably best made for doing so during pregnancy. There is some comfort to be had from these studies in that post natal exposure of children to pesticides was not linked to cognitive problems. Pregnancy is a special period indeed.

Obviously the best way to reduce pesticide exposure is to reduce pesticide use. One way to do this is through genetic modification. Implanting a gene from the Bacillus thuringensis bacterium that codes for the production of an insecticidal protein has been proven to be effective. This protein is harmless to humans but kills insects when they consume it. Implementation of Bt technology in China has already resulted in a 25% decrease in organophosphate use. Researchers around the world are working on safer pesticides, but as with all chemical issues, it comes down to a risk-benefit evaluation. And that evaluation is more critical during pregnancy. So if you are a developing fetus, and you sense mommy smoking or drinking, or chasing cockroaches with an insecticidal spray, give a good kick.

Polycarbonate is Polyfunctional

Chemical Institute of Canada — Wed, 17 Nov 2010 02:45:06 GMT

You really have to do something major to have a street named after you. You can thrill the world with music, you can make an impact in politics, you can become a star athlete, or like Daniel Fox, you can invent a plastic. Dan Fox Drive in Pittsfield Massachusetts is a tribute to the man who gave the world polycarbonate, a plastic that was to profoundly alter our lives.

Dr. Fox graduated with a PhD from the University of Oklahoma in 1952 and soon found a job as a research chemist with General Electric in Schenectady, N.Y. At the time G.E. researchers were looking for novel materials to be used as insulation for electric wires but were repeatedly stymied. Every material they tried deteriorated when exposed to water. It was at this point that Fox remembered a curious substance he had encountered in graduate school.

Fox had been working with guiacol, a compound that was found in creosote, the black oily guck that builds up inside chimney flues as a result of incomplete burning of wood or coal. There was interest in guiacol because of its potential to be converted into compounds that had applications in the pharmaceutical and food industries. Guiacol itself had antiseptic properties and also served as a potential raw material for the synthesis of vanillin, the major flavour component of the vanilla bean. As part of his research, Dr. Fox synthesized a number of guiacol derivatives, one of which was guiacol carbonate. Interestingly, this compound resisted breakdown, even in boiling water. At the time this didn’t seem to have any great importance, but now at G.E. Fox was searching for just such a material.

Guiacol carbonate was water resistant all right, but it was a simple molecule that could not be formulated into any sort of a plastic. But Fox understood how carbonates were synthesized and realized that if he started with the right ones he could link them together into long chains, in other words, into “polycarbonates.” There was a good chance that such a polymer would have the properties he desired. Alas, when he mixed his chemicals, all he got was a glob of a material that was so hard he couldn’t even remove his stirring rod. This was certainly not going to be any sort of insulating material. But it was interesting enough to keep around the lab. The blob of glob became a curiosity, sometimes used to drive nails, sometimes thrown down stairs in futile attempts to shatter it. No luck with that.

Hmmm, Fox thought, a plastic that doesn’t break ought to be patented! And in 1955, just two years after he had come across the novel material, Dr. Fox applied for a patent. As is routine with any new patent application, he carried out a patent search and discovered much to his amazement that the German chemical company Bayer had applied for a polycarbonate patent the same year! Apparently Dr. Hermann Schnell at Bayer had independently come up with a plastic almost identical to Fox’s. Since neither patent had yet been granted, the two companies held discussions and forged a working agreement. Whichever company was granted legal priority, it would allow the other one to manufacture polycarbonate as long as appropriate royalties were paid.

As it turned out, this worked in G.E’s favour. The patent was awarded to Bayer since the company was able to document that Schnell had invented polycarbonate a week before Fox gave birth to his discovery. Polycarbonate, it seems, had two legitimate fathers! It wasn’t long before G.E found a use for the new plastic. At the time, the company had a monstrous problem with electrical meter covers then made of glass. Rambunctious teenagers, stones, and glass meter covers were not a good mix, as G.E. found out. But meter covers made of polycarbonate could readily withstand the teenagers’ assaults! Lexan, as General Electric named its polycarbonate, was off and flying. Before long, it was really flying. Into outer space!

Astronauts helmets had to be able to withstand impact at both high and low temperatures, and the visors had to have exceptional clarity. Polycarbonate fit the bill. That “one small step for man, one giant leap for mankind” could not have been taken without polycarbonate. The plastic also leaped into car headlight assemblies, safety glasses, bullet resistant shields, fighter plane canopies, skylights, and “unbreakable” bottles. A polycarbonate tunnel allowed visitors at SeaWorld to walk through a shark tank. Many viewed the predators through lightweight, shatterproof plastic eyeglasses made of polycarbonate.

Then along came the electronic age, essentially made possible by polycarbonate. Computer casings, cell phones, and perhaps most importantly, compact discs and DVDs are all made of this remarkable plastic. It’s the only one that meets the strength, weight and optical purity characteristics needed for compact audio and video discs. Our life would truly be different without this plastic. In more ways than one.

The raw material needed to make polycarbonate is bisphenol A (BPA)! The very same compound that has made headlines because of its potential toxicity. Traces of BPA show up in our blood and urine, which is no surprise given that it is impossible to keep a chemical that is produced in such massive amounts from escaping into the environment to some small extent. But most of our BPA exposure actually comes from food, basically through the leaching of trace amounts from the epoxy resin that lines the inside of food cans. Like polycarbonate, it is formulated with bisphenol A.

The canning industry is frantically searching for a replacement, even though any effect of BPA on humans is controversial, to say the least. Contrary to some claims, BPA does not build up in the body, the amount we take in is equal to the amount we eliminate in the urine. Still, replacing the epoxy resin in can linings is a reasonable application of the precautionary principle. But clamoring for the total elimination of BPA is unrealistic, unscientific and unnecessary. Unless, that is, we’re ready to forget about our hockey and bicycle helmets, laptops, CDs, DVDs and cell phones.

Copper Sulphate, Swimming Pools and Vineyards

Chemical Institute of Canada — Tue, 31 Aug 2010 22:20:20 GMT

Algae often invade swimming pools and make for greenish, cloudy water. A very small amount of copper sulfate added to the water improves the clarity and makes the pool more inviting. There is another benefit: the use of copper sulphate will cut down on the amount of chlorine or bromine used to disinfect the pool. Copper sulphate at such dilutions is an extremely safe substance and has been given a clean bill of health by the Pest Management Regulatory Agency of Health Canada. This agency also regulates a completely different use for copper sulphate. It can be used to control "downy mildew fungus" which can devastate grapevines. It frolics in wet weather and first shows up as a downy patch on the bottom of the leaf. If rain persists, it becomes established and can destroy the crop and even carry over into the next season. In the 1860s, Pierre-Marie-Alexis Millardet, a professor of botany at the University of Bordeaux discovered that a mixture of copper sulphate and lime effectively eliminated the fungus. How did he discover this? Farmers had long been spraying vines with the mix to produce unappetizing grapes to deter thieves. Millardet noted that these vines had no fungal growth. The combination of copper sulphate and lime came to be known as Bordeaux mixture and became the first commonly used fungicide. Because it is made from naturally occurring minerals it can be used in organic agriculture. This in spite of the fact that toy companies who make chemistry sets will not include copper sulphate because they judge it to be too dangerous! Growing beautiful blue crystals of copper sulphate used to be a common science activity for students but now if they want to pursue this activity they have to purchase the copper sulphate in a health food store where it can legally be sold as an organic fungicide.

The Chemical Defense of the Bombardier Beetle

Chemical Institute of Canada — Sun, 15 Aug 2010 13:31:16 GMT

Based on their ability to discharge “chemical bombs” when threatened, bombardier beetles are aptly named. Beetles are different from other insects in that while they can fly, they cannot do so instantly. Their wings are stored under wing covers and have to be released before they can take to the air. Sort of like Clark Kent having to shed his everyday clothes before becoming Superman. Since beetles cannot instantly fly away when attacked, they have evolved emergency defenses to use while they plot their getaway.

The African bombardier beetle, Stenaptinus insignis, has been extensively studied to understand its remarkable defense system. When attacked by predators, mostly ants, the beetle unleashes bursts of its hot chemical spray accompanied by audible detonations. The spray originates from a turret-like appendage under its abdomen which the beetle maneuvers to achieve remarkable accuracy. But it is the chemistry of the spray that is truly amazing. The irritant chemical is formed just prior to launch by mixing the contents of two separate glands. One contains hydrogen peroxide and hydroquinone, while the other harbors a mixture of enzymes known as catalases and peroxidases that can react with hydrogen peroxide to form oxygen gas and water. When the contents of the two glands are mixed, oxygen forms and in turn reacts with hydroquinone to convert it to benzoquinone. This reaction is so highly exothermic that the chemical mixture can reach a temperature of 100 degrees C. Pressure due to the buildup of oxygen then causes the hot mixture of water and benzoquinone to be expelled with a “pop,” much to the woe of any attacking ants.

Bombardier beetles can launch their chemical “bombs” up to twenty times before running out of ammunition. But by that time they will have succeeded in unfurling their wings and are ready to leave their attackers behind wallowing in their hot, toxic wake. While bombardier beetles have been able to free themselves of ants, they have not been as successful with creationists who argue that the existence of these arthropods is proof of the theory of creation. Why would separate glands have evolved, they ask, when it is clear that there is no evolutionary advantage until their contents are mixed? The beetle must therefore have been created as is, ready to fight off predators. Evolutionists don’t buy the argument. They say that the beetle is actually an excellent example of survival of the fittest. Random mutations over many years resulted in the protective mechanism that increased the chances for survival-the essence of evolution. Whatever be the case, nobody can contest the fact that the bombardier beetle is in possession of an impressive chemical weapon. So if you encounter one, leave him be.

Swimming in Stearyl Alcohol

Chemical Institute of Canada — Tue, 13 Jul 2010 03:22:34 GMT

Nobody likes to swim in cold water but heating a pool is expensive. Solar blankets can help, but it’s a pain to drag them on and off. But how about a liquid pool cover? Believe it or not, that‘s a possibility! Just throw a plastic dispenser of stearyl alcohol into the water, usually in the shape of a fish, and you can cut down on heat loss. The stearyl alcohol, released at a controlled rate by a microprocessor in the dispenser, rises to the surface of the water where it forms a layer that is only one molecule thick, known as a “monolayer.” This acts as a sort of lid on the water and keeps it from evaporating. And evaporation leads to heat loss, as anyone who has spilled alcohol or acetone on their hand can testify. It takes energy to convert a liquid to a gas, and that energy is drawn from the surroundings. When water evaporates from the surface of a pool, the remaining water loses heat. Since the monolayer of stearyl alcohol retards evaporation, it helps to keep the water from losing heat. But don’t expect to convert a pool into a hot tub. Remember that stearyl alcohol does not heat the pool, it only slows the rate of cooling.

Of course any time a chemical is added to the water in a pool, safety issues have to be considered. Stearyl alcohol is in fact so safe that it is sometimes even added to drinking water reservoirs to slow the loss of water to the atmosphere. It is also widely used in cosmetic creams and lotions at concentrations way above that found in swimming pool water without any safety problems. Here it acts as an emulsifier and emollient. Emulsifiers are molecules that have one water soluble end and one oil soluble end and allow oily compounds to mix with water. That is exactly what is needed to formulate a cream or lotion.

Emollients on the other hand soften the skin by preventing moisture loss. In this case stearyl alcohol performs the same job as in a pool. It accumulates in the top layer of the skin and keeps moisture from evaporating. Some people avoid skin care products that contain alcohol because they worry about a drying effect. That is a legitimate concern with ethanol and isopropanol, because these are small molecules that readily evaporate from the surface of the skin and actually encourage water evaporation. Such is not the case with the so called “fatty alcohols” like stearyl or cetyl alcohol. These large molecules that do not evaporate readily. The reason they’re called fatty alcohols is because they are produced from fats. Stearic acid, for example, is readily prepared by heating animal or vegetable fats under alkaline or acidic conditions. It can then be converted to stearyl alcohol by catalytic hydrogenation, ready to be dispensed from a plastic fish to improve the comfort of your swim, or from a bottle or jar to make your skin feel nice and smooth after that swim.

Sulphites in the Dishwasher

Chemical Institute of Canada — Wed, 30 Jun 2010 20:51:58 GMT

Have you ever wondered why detergents for automatic dishwashers contain sodium sulphite? It has nothing to do with cleaning dishes. The sulphite protects the dishwasher! Iron reacts with oxygen to form ferric oxide which is better known as rust. This reaction proceeds more readily at high temperatures, as found in washing machines. Where does the oxygen come from? It is dissolved in water.

The surface of water is in contact with air, so some oxygen can always dissolve. Oxygen also is a byproduct of photosynthesis which of course occurs as aquatic plants grow. The amount of oxygen that dissolves depends on the temperature (less dissolves as the temperature increases), the pressure (less dissolves at higher altitudes) and the amount of other substances already dissolved in the water (freshwater holds more oxygen than salt water). Oxygen in water is a good thing for fish since they can meet their oxygen needs by extracting the gas as water passes through their gills. But it is not so good for metals in washing machines!

Sodium sulfite is an oxygen scavenger. It reacts with oxygen to form sodium sulfate and effectively lowers the dissolved oxygen content, thereby protecting the insides of washing machines from rusting. Such corrosion may be an annoyance at home but it is a huge problem in industrial boilers. Sodium sulphite is commonly used here as well, although in high pressure boilers it presents a problem. It can break down to form sulphur dioxide along with hydrogen sulphide which not only smells like rotten eggs but is itself corrosive. Alternatives are available. Hydrazine, N₂H₂, is a liquid that can be added to boiler water to virtually eliminate dissolved oxygen. It reacts with oxygen to yield nitrogen gas and water, neither of which present a problem. But hydrazine is a pretty nasty stuff to work with so less toxic compounds are desirable.

An interesting possibility is sodium erythorbate which reacts with oxygen to produce lactic and glycolic acids which themselves can react with oxygen eventually yielding carbon dioxide. You may have encountered sodium erythorbate elsewhere. In hot dogs! It serves double duty here. Sodium erythorbate is a preservative and allows for less nitrite to be used. It is also, as we have seen, an oxygen scavenger and prevents the formation of off-flavors which can be produced as meat components react with oxygen. Incidentally, there is absolutely no truth to the rumor that sodium erythorbate comes from earth worms. This probably resulted from someone noticing a similar pronunciation between “eryth” as “earth” and jumping to the wrong conclusion.

Air Bag Chemistry

Chemical Institute of Canada — Tue, 22 Jun 2010 01:27:48 GMT

How can automobile airbags inflate in a few milliseconds? With some clever chemistry! When sodium azide, NaN_3, is ignited by a spark, it releases nitrogen gas which can instantly inflate an airbag. The problem, however, is that the reaction also forms sodium metal which reacts with moisture to generate sodium hydroxide, a highly corrosive substance. A burst airbag can therefore wreak havoc. Chemical ingenuity, however, comes to the fore. If potassium nitrate and silicon dioxide are also included with the sodium azide, the only products that form in addition to nitrogen are potassium silicate and sodium silicate. Both of these are inert, harmless substances.

An airbag is designed to release some of the gas just after it deploys to help cushion the impact against the body. Hitting a fully inflated, unyielding airbag, though, could be catastrophic. So before widely promoting this protective device, the safety of the contents had to be ascertained. In the 1970s Mercedes settled this issue by putting a cage full of canaries in a car and deploying an airbag. Canaries are extremely sensitive to minute traces of toxic gases, but the birds survived the experiment with no casualties. By the late 1980s airbags had become a common feature in automobiles and have since saved thousands of lives.

But, like with any other scientific advance, there is a “but.” Airbags are not problem-free. While the chemistry involved in curbing sodium hydroxide production is clever, it is not foolproof. Small amounts of the caustic material have been released from deployed airbags, in rare cases causing severe eye injuries, including blindness. The most serious concern, however, is damage that can be done by an airbag as it rockets out at an astounding speed of up to 330 km per hour. A blow to the head by the rapidly inflating bag can be lethal. Unfortunately, over a hundred people, mostly children and small adults, have been killed in this fashion, ironically sometimes in low speed collisions when lives were not at risk. There is a great deal of research underway to find ways to ensure that airbags are only deployed when necessary and that they are deployed in the safest way. This includes various sensors that can gauge the weight of the passengers to allow a computer to calculate how and if an airbag should be inflated. In any case, children must not be allowed to sit in the front seat of an airbag equipped car! Some researchers even argue that better protection can be had by stronger promotion of seat belts than by emphasizing airbags.

There is a further problem that needs to be addressed. Sodium azide is more toxic than cyanide. What will eventually happen to all the azide in cars headed for the junk heap? What if the canisters are not removed? If sodium azide is released, it can react with water to form hydrazoic acid which is not only toxic, but is highly explosive. Sodium azide can also react with metals such as copper or lead to form explosive copper or lead azides. Just ask the plumbers who were called to a lab where sodium azide solutions had been used. When they took out a piece of copper pipe and tossed it into the garbage it exploded. An unfortunate and shocking way to learn about the chemistry of azides!

Statistics

Chemical Institute of Canada — Wed, 09 Jun 2010 03:34:33 GMT

I like statistics - at least the ones that make sense. One oft-quoted phrase about these mathematical manipulations is:‘There are lies, damn lies - and statistics’. This has been attributed to Mark Twain, Benjamin Disraeli and Winston Churchill (amongst others), although it seems that Churchill only wished he had coined the remark.

Statistics are used by just about everyone from baseball enthusiasts and medical practitioners to newspaper reporters. One number that caught my eye recently was the claim that about five trillion cigarette butts are discarded each year. Before passing this remarkable number along to colleagues, (1 followed by 12 zeros) I thought I’d do a quick “back-of-the-envelope” calculation. This is a technique popularized by Enrico Fermi, one of the many brains behind the development of the atomic bomb. He would make a rough calculation on a scrap of paper to see if the numbers associated with some proposed process were in the right ballpark.

Let’s see - assuming there are seven billion people in the world, of whom, estimating conservatively, one billion smoke at a rate of 10 cigarettes a day for a year, we come up with a total of about 3.7 trillion cigarettes. Cough..cough. Thus, the reported number and my estimate are not that far from each another. They are of the same “order of magnitude,” meaning that they do not differ by a factor of ten.

If we assume that the original number of five trillion is correct, then the weight of those butts would be five trillion times the weight of one butt. So off I went looking for butts on the street. It did not take long to find a few and weigh them. The average was about 0.15 grams. This means that about 1.6 billion pounds of butts are discarded each year, translating to some 800,000 tons. That’s roughly the weight of half a million automobiles chopped into very small bits and spread all over the world. Another way to put this would be that the weight of all those cigarette butts is about equal to the weight of all of the vehicles registered in the Province of New Brunswick.

The above calculations were done by making reasonable estimates and doing one weighing of a few butts and taking an average. Admittedly, having a sensitive balance available is not so common, but even that estimate could have been made by just going to Google and asking the question. One cigarette weighs a bit less than one gram, so one-sixth of that (reasonable estimate) is about 0.15 grams. The point is that unusual statistics can often be checked by an individual, either by back of the envelope calculations or by inserting a few key words into Google. For example, in this case, just Googling the words “how many cigarette butts”-yielded the desired result. The second listing was a site based on U.S. Department of Agriculture data and verified the total cigarette number along with the weight of the filters. That site also revealed that the total world production of cigarettes has been essentially constant over the past 20 years.

The real message here is that an individual can often make a decent estimate of a statistic, but these days, a search engine will quickly corroborate of refute the number. It is important to not simply pass on data seen in the press without some simple checking of the facts. It should also be pointed out that the butt of a cigarette is made of cellulose acetate, a material that does not easily biodegrade. Estimates of how long these stick around to annoy us range from 1 to 15 years. But don’t trust me. Check it out.

Dr. David Harpp
McGill University

Chemical Structure

Chemical Institute of Canada — Sat, 29 May 2010 18:09:56 GMT

“Chemical structure” is a phrase that is not often heard unless one is in a chemistry class. Yet, it is the specific arrangement of atoms in a molecule, its “structure,” that governs its properties. Most people have heard of benzene, a natural constituent of crude oil and a known carcinogen. (Benzine, a mixture of hydrocarbon molecules like gasoline is a different substance). Benzene has six carbon atoms bound in a hexagonal arrangement, each linked to a hydrogen atom. It is like a hexagonal plate with spikes. Benzene is a liquid, but insert one oxygen atom in between one of the carbons and the hydrogen and you create phenol, a completely different molecule. Phenol is a solid, has disinfectant properties and is a present as an odour component (30 ppm) in a certain scotch whiskey. In the late 1800s, it was used in dilute form in the operating room and eventually led to germ-free techniques during surgery. Sadly, it was used by the Nazis in World War II as an extermination agent when injected in gram quantities.

The point here is that simply adding one atom of oxygen to benzene in a specific location in the molecule, dramatically alters its physical and biological properties. The pharmaceutical industry endlessly produces drug candidates by carefully changing the chemical structure of compounds that have potential medical properties. Changing the length of a carbon atom chain is one kind of subtle alteration that leads to altered physical and biological properties.

The giant molecule of hemoglobin, transporter of oxygen in the body, is made of several thousand atoms in a very specific arrangement. A small change in one corner of this molecule, the elimination of a couple of carbon atoms and an oxygen, signals a genetic blood disorder called sickle cell anemia. This subtle change causes the blood cell containing the altered hemoglobin to stick to a neighbor, impairing blood flow. It is amazing that such a devastating disease can be caused by a small change in chemical structure, caused in turn by a mutation in the hemoglobin gene.

So when you hear a discussion where the phrase “chemical structure” crops up, it is likely to be concerned with an important topic, not just with some esoteric phenomenon. Indeed, our very lives depend on the exact ways in which atoms are joined together.

By Dr. David Harpp

McGill University

Organophosphate Concerns

Chemical Institute of Canada — Tue, 25 May 2010 03:22:07 GMT

In 1939, Gerhard Schrader, a German chemist, was searching for better methods to control insects when he chanced upon a substance, chemically an organophosphate, that had greater insecticidal activity than anything he had ever seen. He named the new compound "Tabun" and envisioned a breakthrough for agriculture. Hitler, however, had something else in mind for the newly developed substance. If it could kill pests, it could also kill people. A terrible new weapon was born. Tabun was actually a colorless, odorless, relatively volatile liquid. Exposure to a few milligrams was enough to cause death. It penetrated through intact skin without any irritating effect so that a fatal dose could be absorbed with no warning.

The term "nerve gas" was used to describe the substance because of its mechanism of action. The chemical interferes with the way information is transmitted from one nerve cell to another. Such transmission involves the release of chemicals called neurotransmitters from a nerve ending followed by the migration of this substance across the tiny gap separating nerve cells, known as the synapse. The neurotransmitter then stimulates an adjacent cell by fitting into a "receptor site" on its surface, very much as a key fits into a lock. This cell then releases a neurotransmitter which stimulates the next cell, and thus the message is propagated. The specific neurotransmitter involved in the nerve gas story is acetylcholine.

Once acetylcholine has carried out its job of triggering a reaction in an adjacent cell, it is decomposed by an enzyme present in the synapse. Overstimulation is therefore prevented. It is this enzyme, acetylcholinesterase, that is inactivated by nerve gases. The result is overstimulation of the nervous system, eventually leading to convulsions, paralysis and respiratory failure. The Germans never managed to use organophosphates in warfare but Schrader’s vision of these compounds as effective insecticides proved to be correct. As DDT and other organochlorides fell into disfavor in the 1960s because of concerns over their persistence in the environment, the organophosphates, which break down much more readily, gained popularity to the extent that today roughly 70% of all pesticides used belong to this family.

It goes without saying that organophosphates are toxic compounds, that of course is what makes them effective pesticides. It also goes without saying that our extensive reliance on organophosphates to protect our homes and food supply from insects means that we can’t escape exposure to these compounds. Urine analysis confirms that most of us have organophosphate breakdown products cruising through our bodies. The amounts are way too little to cause acute effects but there is the lingering worry about what exposure to traces of organophosphates may do in the long run. And now a study by researchers at the University of Montreal, published in the journal Pediatrics, suggests that organophosphates may be linked with attention deficit hyperactivity disorder (ADHD).

The study involved analyzing single urine samples from 1139 children aged 8 to 15 for organophosphate metabolites. Some of these children, 148 to be exact, met the criteria for a diagnosis of ADHD, and interestingly they were more likely to have higher urinary levels of organophosphate breakdown products. Such an association cannot prove cause and effect; it may be possible, for example, that children who have ADHD metabolize toxins differently or that their liquid intake may be different, altering the concentration of chemicals in the urine. But it is also possible that organophosphates really can be a causal factor in ADHD. After all, it is clear that these compounds have an effect on the nervous system and ADHD is likely a nervous system disorder. Still, it must be remembered that this study was based on analyzing a single urine sample and there was no indication about the extent of exposure to household pesticides. It is therefore premature to blame pesticide residues on food for an increase in ADHD, but we can’t absolve them of blame either. Eating organic produce reduces exposure, and is a good option as long as the extra expense doesn’t lead to consuming fewer fruits and vegetables. More important is to be very careful about using pesticides around the home and to resort to organophosphates only if absolutely necessary. Finally, ADHD is a complex condition with many possible causes ranging from genetic factors and consuming certain food additives to early exposure to lead, nicotine or alcohol.