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A Mechanism in Common

• N 1891 A SHY 24-YEAR OLD POLISH GIRL named Marya Salomee I Sklodowska, arrived in Paris with the dream of becoming a scientist. In I the chauvinist academic culture of France at the time, such a dream stood little chance of fulfilment, but Marya possessed a brilliant mind and

stubborn determination. Nor was she a stranger to hardship. The Poland of her youth was occupied by the Russians, and her mother had died when she was just four. The youngest of five children, she had been raised

in poverty by an idealistic father, and educated in the Flying University, which met each week in different locations to avoid detection by the Russians — the Poles resisted oppression through education, and Polish

culture flowered in underground centres of learning. Not surprisingly, the passion for learning that swept her homeland left an indelible mark on Marya.

When she was 18, Marya made a pact with her sister Bronya. Bronya would pursue her own dream of studying medicine in Paris, and Marya would support her by working as a private tutor in Warsaw; then Bronya would return the favour. Marya duly worked as a governess for six years, while continuing her underground studies in chemistry and mathematics and suffering an unhappy love affair. In the meantime, Bronya completed

medical school and married a fellow medical student. So it was that Marya arrived as a mature student in Paris, changed her name to the French

C H A P T E R S I X

Oxygen Poisoning and X-lrradiation: A Mechanism in Common • 107

version, Marie, and enrolled at the Sorbonne. She passed a master's degree in physics with flying colours in 1893, and a second in mathematics in 1894. Then, while seeking extra laboratory space to conduct more elaborate experiments, she was introduced to an equally brilliant, intro-verted and free-thinking Frenchman, who had already made a reputation

for his work on crystallography and magnetism. They quickly fell in love, and he wrote to her saying how nice it would be "to spend life side by side, in the sway of our dreams: your patriotic dream, our humanitarian dream and our scientific dream." Marie and Pierre married in 1895, going on a cycle tour around France for their honeymoon, and when Marie found fame as a scientist it was under her new name, Marie Curie.

In the next two years, Pierre gained a teaching position at a science college while Marie studied for a teaching certificate. In 1897 their first child, Irene, was born, and that same year Marie began work on her doctoral studies — another pioneering step for a woman at the time;

she was to become the first woman in Europe to receive a doctorate in science.

Although both Marie and Pierre had been interested primarily in magnetism until then (and the field still pays homage to their name in the 'Curie point', the temperature at which materials lose their mag-netism), the Curies had become close friends with another brilliant young French scientist, Henri Becquerel. Inheriting the large phosphorescent mineral collection of his scientist father, Becquerel had just discovered that if crystals of uranium sulphate were exposed to sunlight, then placed on photographic plates and wrapped in paper, an image of the crystals would form when the plates were developed. At first he assumed that the

rays emitted by the crystals were a type of fluorescence derived from the sunlight, but this theory was confounded by the overcast skies of Paris that February. Becquerel returned his equipment to a drawer and waited for better weather, but after a few gloomy days he decided to develop his plates anyway, anticipating no more than faint images. To his surprise, the images turned out to be clear and strong, and Becquerel realized that

the crystals must have emitted rays even without an external source of energy such as sunlight. He soon showed that the rays came from the small amounts of uranium in the crystals and that all substances contain-ing uranium gave off similar rays. He even found that uranium causes the air around it to conduct electricity. His excitement transmitted to the

Curies, and Marie decided to study the strange phenomenon, which she later termed radioactivity, for her doctorate.

108 • TREACHERY IN THE AIR

Marie set to work on a uranium ore known as pitchblende. She and Pierre had realized that radioactivity could be measured by the strength of the electric field that it generates in the surrounding air, and Pierre invented an instrument that could detect the electric charge around mineral samples. Using this instrument, Marie discovered that the radio-activity of pitchblende was three times greater than that of uranium, and concluded that there must have been at least one unknown substance in pitchblende, with a much higher activity than uranium. By chemically separating the elements from uranium ore and measuring their radio-activity, the Curies discovered a new element that was 400 times more radioactive than uranium, which they named polonium after her native Poland. Later, Marie discovered tiny quantities of another element, this time a million times more radioactive than uranium, and called it radium.

Pierre tested a tiny piece of radium on his skin, and found it caused a burn, which developed into a wound. The Curies recognised its potential as an anti-cancer treatment. Radium was first used for this purpose by S. W. Goldberg in St Petersburg, as early as 1903. Radium needles are still inserted into tumours as a cancer therapy today.

To study the properties of radium in detail, the Curies needed to isolate more, and to do this entailed working with tonnes of pitchblende to isolate just a few milligrams of radium. Radium is present in such small quantities that, even today, world production amounts to only a few hundred grams. The Curies worked in what must have been appalling conditions. Their lab was described by a contemporary chemist as looking

more like a stable or a potato cellar. Refusing to patent radium, for human-itarian reasons, the Curies continued to struggle on. Despite their financial hardship and poor conditions, they took great pleasure in their work, especially at night, when they could see all around them "the luminous silhouettes of the beakers and capsules that contained our products."

For their work on natural radioactivity, the Curies and Becquerel received the Nobel Prize for physics in 1903. The year after that, Marie and Pierre had a second daughter, Eve. It must have been the best time of their lives. In 1906, Pierre, weakened by radiation, was killed in a

road accident, his head crushed beneath the wheel of a horse-drawn cart.

Traumatized, Marie began writing to him in a diary, which she kept for many years, but her scientific resolve did not falter, and she determined to complete alone the work they had undertaken together. She struggled against the French establishment for recognition, finally taking up her husband's old position at the Sorbonne in 1908 — the first woman in its

Oxygen Poisoning and X Irradiation: A Mechanism in Common • 109

650-year history to be appointed professor there. In 1911 she received a second Nobel Prize, for the isolation of pure radium, and in 1914 she founded the Radium Institute, now renamed the Curie Institute, with its humanitarian goal of easing human suffering. Throughout the First World War she trained nurses to detect shrapnel and bullets lodged in wounds, using mobile x-ray vans, and after the war, with her daughter

Irene alongside her, she pioneered the use of radium to treat cancer patients. Irene herself, with her husband Frederic Joliot, went on to receive a Nobel Prize for the discovery of artificial radioactivity in 1935.

Marie did not live to see her daughter's Nobel laurels. She died of leukaemia on 4 July 1934 at the age of 67, exhausted and almost blinded by cataracts, her fingers burnt and stigmatized by her beloved radium. She had not been the first to die of radiation poisoning, nor was she the last.

During the 1920s, several workers at the Radium Institute had died of a cancer that other doctors attributed to radioactivity. Not believing the truth, Marie put it down to a lack of fresh air. Later, her daughter Irene also died of leukaemia.

Today, with the experience of Hiroshima and Chernobyl behind us, radiation is not seen in quite the same humanitarian light. High doses of radiation kill cancer cells, but also kill normal cells. Within weeks of the discovery of x-rays there had been reports of tissue damage among researchers who worked for many hours a day with x-ray-producing dis-charge tubes. Many of them lost their hair and developed skin irritations, which sometimes festered into severe burns. Lower doses of radiation were found to

increase

the risk of cancer. The signs were there even in Marie Curie's time. Forty per cent of the early researchers in radioactivity died of cancer. They were joined by others who worked with radioactive materials. In 1929, doctors in Germany and Czechoslovakia noticed that 50 per cent of the miners working in Europe's only uranium mine, in Bohemia in northern Czechoslovakia, had lung cancer, which was attributed to their inhalation of radon gas, a radioactive decay product of uranium (via radium), escaping from the ore. The incidence of lung cancer among uranium miners in the United States was also much higher than normal.

An awful fate befell many of the young women hired to paint radium onto the dials of watches, so that they would glow in the dark. The original luminous watches had been designed for soldiers fighting in the trenches during the First World War, but their novelty stimulated a

110 • TREACHERY IN THE AIR

consumer fad in the 1920s. To point the tips of their paint brushes, the girls were taught to moisten the bristles with their lips. At the time,

radium was still hailed as a panacea and was sold for a variety of medical purposes, as elixirs, snake oils and aphrodisiacs. The, girls were told that radium would put a glow in their cheeks and give them a smile that shone in the dark, and they would sometimes paint their nails, lips and teeth.

Within a year their teeth began to fall out and their jaws disintegrated.

When they began to sicken and die in large numbers, doctors found that their bodies, even their bones, contained large amounts of radon and other radioactive substances. Not surprisingly, the watch companies rejected the link and government regulators concluded that existing evidence did not warrant further investigation. An editorial in the New York World called a trial in 1926 "one of the most damnable travesties of justice that has ever come to our attention."

Although the watch companies eventually agreed to pay token finan-cial compensation, they never admitted their guilt or submitted to formal

regulation. One worker, Catherine Wolfe Donahue, sued the Radium Dial company in 1938. She testified in a Chicago courtroom that she and a co-worker had once asked their supervisor, Rufus Reed, why the company had not posted the results of the physical examinations that had been carried out during the 1920s. Reed had apparently responded: "My dear

girls, if we were to give a medical report to you girls, there would be a riot in the place." The medical community finally instituted a dose limit for radon in 1941, but the confusion and vested interests had concealed the delayed effects of radiation, and few people, even within the Manhattan Project that built the first atomic bomb, predicted the full horror of nuclear fallout.

Nuclear fallout is the settling of unconsumed radioactive waste left over from the atomic blast, and can be dangerous for a long time. The explosion causes intense firestorms and whirlwinds stretching high into the air, and the atmospheric disruption often provokes rain. After both Nagasaki and Hiroshima, the air was so full of radioactive ash that the rain was dark and tarry — the infamous 'black rain'. In Hiroshima, the black rain fell over a wide area that stretched from the centre of the town to the surrounding countryside, polluting water and grass alike. Fish died in the rivers, cows died in the fields.

Tens of thousands of survivors of Hiroshima and Nagasaki, who were uninjured by the initial blast, found they had not escaped the bomb after all. Within days, their hair began to fall out and their gums began to

Oxygen Poisoning and X-lrradiation: A Mechanism in Common • 111

bleed. The victims suffered from bouts of extreme fatigue and excruciat-ing headaches. They were weakened by nausea, vomitexcruciat-ing, anorexia and diarrhoea. Painful sores filled their throats and mouths. They bled from the mouth, nose and anus. Those with the most acute symptoms died in a few months. Others were blinded by cataracts in the space of two years.

Many died from cancer years, or even decades, later. Leukaemia is the cancer most commonly linked with radiation poisoning. The

character-istic 'blue stigmata' of radiation victims are a sign of leukaemia. The stigmata are formed by clumps of proliferating white blood cells. For 30 years after the nuclear bomb, the number of cases of leukaemia in

Hiroshima remained 15 times higher than the rest of japan. The inci-dence of other cancers with longer incubation periods, such as lung, breast and thyroid cancer, all began to rise after about 15 years.

As the threat of nuclear war has receded, safety concerns about nuclear power plants and other potential sources of radiation have

sharpened in focus. Confidence in reactor safety was undermined by two serious accidents, one in 1979 at the Three Mile Island nuclear power plant in Pennsylvania and the other in 1986 at Chernobyl in the Ukraine.

Chernobyl was the worst reactor accident in history, with 31 people dying of direct radiation poisoning, and thousands more exposed to high doses of radiation. Even without accidents, fears of leakage and contamination are increasing. In England, reprocessing of nuclear waste at Sellafield has

raised legitimate concerns about the high incidence of leukaemia in nearby villages. Other groups exposed to above-normal levels of radiation are also at higher risk of leukaemia. The so-called Balkan War syndrome

(claimed by some to be a form of leukaemia) among troops who had been stationed in Kosovo, and among potentially thousands of local people, is attributed to the use of armour-piercing depleted-uranium shells. Even commercial aircrews may have a relatively high risk of leukaemia, as they are subjected to higher levels of cosmic radiation at flight altitudes.

With such a history, it is not surprising that even medical x-rays and radiotherapy generate fears, sometimes hysteria, about radiation poison-ing. No nuclear power stations have been built in the United States since the late 1970s. The existence of a 'safe' radiation dose has been debated for decades without consensus. As one expert puts it, the most practical approach is to limit human exposure to ionizing radiation and hope for the best.

112 • TREACHERY IN THE AIR

What has all this to do with oxygen, you may be wondering? The answer is that radiation exerts its biological effects through a mechanism that is very similar to the effects of oxygen poisoning. The mechanism hinges on an invisible thread of reactions, linking oxygen to water. The lethal effects of radiation and oxygen poisoning are both mediated by exactly the same fleeting intermediates along this pathway. These intermediates can be produced from either oxygen or water (Figure 7). In radiation poisoning, they are produced from water, in oxygen poisoning from oxygen. How-ever, normal respiration also produces the same reactive intermediates from oxygen. Respiration can therefore be seen as a very slow form of oxygen poisoning. We shall see that both ageing and the diseases of old age are caused essentially by slow oxygen poisoning.

The fleeting intermediates produced by radiation and respiration are called

free radicals.

We discussed them briefly in Chapter 1. Later in the book, we will refer to free radicals many times. I use the term rather

loosely for convenience. Not all of these fleeting intermediates are free radicals within the usual definition of the term. Applying the correct terminology, however, is cumbersome. Another umbrella term, 'reactive

oxygen species', is even more cumbersome and also untrue — not all are especially reactive and some, such as nitric oxide (NO) are technically reactive nitrogen species. A third possible term, oxidants, is also incorrect:

Figure 7: Schematic representation of the intermediates between water and oxygen. Only changes in the number of electrons (e~) are shown in each direction. The reactions also depend on the availability of protons, although this is not shown for simplicity. Because protons are positively charged, electron rearrangements tend to lead to compensatory proton

rearrange-ments.

Oxygen Poisoning and X-lrradiation: A Mechanism in Common • US

the superoxide radical, for example, is more likely to act in the opposite way (as a reductant). Given these difficulties with definitions, I will stick with the name free radicals.

To follow the argument in the rest of the book, all you really need to know is that free radicals are reactive forms of oxygen, produced continu-ously at low levels by respiration. However, this definition is over simple and inexact. In the rest of this chapter, then, we will take a closer look at what free radicals are, and how and why they are formed.

The splitting of water by radiation was first described by Becquerel, who began experimenting with radium soon after Marie Curie had isolated workable quantities. In the late 1890s, Becquerel had classified the known

radioactive emanations according to their penetrating power. Emissions that are stopped by a sheet of paper were termed

alpha rays

(they are in fact helium nuclei); those stopped by a millimetre-thin sheet of metal were called

beta rays

(now known to be fast-moving electrons); and those

penetrating a centimetre [2/5 inch] of metal were called

gamma rays

(electromagnetic rays, analogous to x-rays). AH three types of radiation displace electrons from atoms, which gives the atoms an electric charge.

This is why the Curies could detect an electric field in the air around pitchblende. The loss or gain of electrons, giving a substance an electric charge, is called

ionization,

hence the term ionizing radiation. Radiation also produces many other effects, including heat generation, electron

excitation, breaking of chemical bonds and nuclear reactions, such as nuclear fission, as we saw in Chapter 3.

Becquerel discovered that radium emits alpha rays and gamma rays.

These decompose water into hydrogen and oxygen. The decomposition of water was not in itself unexpected, as water had been shown to consist of a combination of hydrogen and oxygen by Laplace and Lavoisier in the 1770s. However, radiation cannot dissociate water directly into hydrogen and oxygen gases (which are made up of molecules of hydrogen and oxygen — H2 and 02 — each containing two atoms), because the ratio of

hydrogen to oxygen atoms in water (H20) is wrong:

H 2 0 - • H2 + O z

Most people will remember having to balance chemical equations at

Most people will remember having to balance chemical equations at