Home Engineering The dark side of technology
More examples of our sensitivity to trace contaminants
Further, we often respond to unbelievably small quantities of chemical signals, so correlations between negative (or positive) effects may be difficult to quantify. Because such sensitivity could not be detected until relatively recently, the manufacturers and users may still be ignorant of the possibilities. I apologize for repeating the point that minute quantities of chemicals can be highly efficient in producing changes, but it is an incredibly important factor that seems unknown to most people, not least as ‘it seems like science’, and many people automatically assume they will not understand, and so do not even listen.
Catalysis, enzymes, diet, and health
During the last century or so, chemists and biologists have realized that many chemical reactions and biological processes operate via the formation of intermediate steps that lower the energy needed to drive the process. In chemistry, the agents that allow this to happen are called catalysts; in biology they are termed enzymes. Catalytic agents are not consumed in the chemistry of the process, but are released at the end of it. So they can start again. Therefore, very small quantities are highly effective. (I have already cited a catalytic example of CFC agents destroying ozone in the upper atmosphere.)
The underlying idea of catalysis needs no understanding of chemistry, as a familiar analogy of these helper chemicals is seen for schoolchildren trying to cross a busy road outside a school. If they just wait for gaps in the traffic they may never be able to cross. So we provide a catalyst, a school crossing warden. The warden walks out with a sign and stops the traffic, allowing the children to freely cross the road at low speed (i.e. a low-energy process). The warden returns to the side and can repeat the process. The overall crossing rate has increased even though the energy needed is low, and the warden can repeat the process hundreds of times.
Catalysts can be even more successful if, rather than taking part in every chemical reaction, they allow a process to start, which can continue and be self-sustaining. Here my warden starts the crossing by stopping traffic, but once started, a long stream of children can continue to cross even if the warden goes away. There are many familiar household demonstrations of such effects. For example, consider ripening of apples or tomatoes: if we put unripe fruit in a drawer with one that is already ripe, the mature fruit emits ethylene, which stimulates ripening of the others—thus they all ripen faster.
The key feature to realize is that if we produce chemical contaminants that play a catalytic role, their effect on our lives, health, and environment may be totally disproportionate to the numbers involved. Rather than only cite negative examples, I emphasize that it is essential to realize that catalysts play a major role in many technologies. Catalysis was part of our industrial history long before anyone realized that such processes existed. Examples range from fermentation of wine, to making vinegar, soap, and leavened bread. Economically they are important; the chemical industries rely on catalytic processes for large-scale production of compounds as diverse as dyes, ammonia, and nitric and sulphuric acids.
Catalysts can be within the material during the chemical reactions. A 100-year-old example was the discovery that nickel particles in vegetable oils could cause hydrogen to bond to the oils. The chemistry may be unknown to most people, but it is now the basis of making margarine; currently the industry produces some 2 million tonnes per year of these hydrogenated materials by this route. Alternatively, catalysts can be attached to a surface and trigger reactions removing passing gases or liquids. This is precisely how platinum particles (and some other metals) in a car exhaust system break down the toxic hot gases of a car engine. Catalytic reactions are also essential at oil refineries for the fragmentation of oil into different compounds, such as diesel, petrol, and aviation fuel.
Biological catalysts, enzymes, control our bodily processes and have a subtle chemistry that usually includes some metallic content. Therefore the intake of these trace elements is essential for all aspects of our health. Probably foremost among these impurities is zinc. Some 200 of the major enzymes include this metal, and there is a long list of medical problems that occur from zinc deficiency. A survey of processes that use zinc enzyme catalysis could occupy a book. Zinc is needed in aspects as diverse as DNA and RNA production, in defence against viruses, fungal infections, and cancer, as well as in growth and reproductive hormones.
There is a particularly large need for zinc intake during pregnancy. An estimated daily requirement is around 15 mg for normal life, but as high as 20—25 mg per day during pregnancy. Vegetarian diets are often particularly weak in offering an adequate zinc intake, although there can be zinc compounds in garlic, dark chocolate, and seeds. To place these quantities in perspective, 15 mg is roughly 30,000 times lighter than a 1-lb steak, or less than one millionth of the total weight of food and drink most people consume each day. A very rough guide is that 15 mg is the weight of just one thousandth of a teaspoonful of salt.
Despite the small quantities of material needed, a large percentage of the population do not manage an adequate zinc intake. Among the many resultant problems, it has been suggested that this deficiency can lead to paranoia and aggression. Indeed, one Nobel Prize winner has suggested that zinc-rich diets should be distributed in areas of the world (such as the Middle East) where there is an inherent shortage of zinc in the diet, but an excess of ongoing conflict. This may be a very perceptive suggestion, and I certainly think it should be tried as an experiment, not least because under normal conditions, a raised zinc intake does not appear to lead to obvious problems. Medical understanding of the role of trace impurities, even those as critical as zinc, have really only been developed over the last 50 years, so the possibility of dietary and rationally controlled improvements in health may appear soon.
A second important trace metal is magnesium, which has a similar chemistry to zinc. Magnesium accumulates to be the fourth most abundant element in the body, as it is found not just in bones and red blood cells, but also in muscles, nerves, and the cardiovascular system. Intake of a minimum amount of magnesium is similarly an essential dietary requirement; however, excessive intake has a number of serious side effects.
Another trace metal often cited is lead. Lead poisoning is thought to have disastrous consequences, ranging from infertility to madness. It has therefore appeared as an unfortunate side effect of economic progress and civilization as we know it (e.g. lead pipes of the Roman Empire or in Victorian Britain). Lead is also an excellent additive in petrol, but the resulting contamination in the exhaust gases is a severe health risk, so lead has been excluded from the petrol in many countries.
Heavy metals, such as lead or mercury, tend to have obvious deleterious side effects on the body and may even cause brain damage. Ingestion of mercury in the form of methyl mercury is well documented. Mercury was used in hat making; sometimes it is claimed the phrase ‘mad as a hatter’ is linked to the fact that hatters could develop neurological problems from the vapour of the mercury they used. Mercury contamination has not totally gone away, as some types of dental fillings are known to have toxic side effects.
There are many ways in which different minerals can enter our diet, and some of the routes are unexpected. For example, there was a fashion at the end of the twentieth century for unglazed earthenware pottery used for dispensing health-food drinks such as orange juice. Unfortunately, orange juice is quite an effective acid solvent, and if left in unglazed pottery it can leach out heavy metals and other elements from the container.
Catalysis is not just important for local industrial and biological processes. A highly important catalytic example is thought to occur in star formation in astronomy. The simplest of building blocks for molecules and compounds is to join two hydrogen atoms together to form a hydrogen molecule. In space, the density of isolated hydrogen is incredibly small, so the chance that two hydrogen atoms could collide, and also have enough energy to react at the very low background temperature, is negligible. Nevertheless, material does accumulate into stars and hydrogen molecules exist. So how does it do it? The assumption is that when a hydrogen atom hits a dust particle, it is weakly bonded to the surface and sticks there for a long time. When a second hydrogen atom arrives, the surface bonding allows the two to meet and form a pair. The modern-day equivalent is an electronic dating agency.
|< Prev||CONTENTS||Next >|