Radioactivity: A Natural Phenomenon C. Ronneau University of Louvain, 51348 Louvain-la-Neuve, Belgium For most of our contemporaries, misinformation is common about radioactivity, even in scientific circles; opinion is unsettled about risks, distrust is the rule, ignorance prevails. Radiochemists and, in general, people handling both chemical and radioactive substances are well aware of the hazards associated with ionizing radiation. Because dosimetly is generally accurate and reliable, the risks associated with operatio& in radioactive environments are clearly defined and recognized. The same is certainly not true for chemical hazards. which are too often overlooked. l had induced a wave of panic After the ~ h e r n o h yaccident over most of Eurooe. I was asked to eive a series of conferences about radioitivity and about tKe consequences of the continent-wide disnersion of radioactive material from the Ukrainian reactor. i realized that, for most people, radioactivitv is totallv unknown as a natural phenomenon: as a consequence, one of the main points to hk emphasized during the lectures was that we all live in a radioactive environment. The second point to he emphasized was that, if radioactivity is natural, any contribution from artificial sources must alwavs he comnared with the natural hackaound in order to dlfine risks.'~hisis a common rule in toxrcology. A few years ago I was discussing with Paul Capron, one of the first Belgian radiochemists, the industrial refuse that was dumped in a nearby site. Naively, I declared that this refuse reputedly contained arsenic. Capron made the straiehtforward observation: "Of course, i t contains arsenic. ever;thing contains arsenic, including our own bodies. AI: ways mention concentrations and compare with natural levels!" This was the general message I decided to convey in the lectures about radioactivity.
The Points To Debate The main points t o debate are summarized on transparencies or on slides and are illustrated by pictures. They are exposed as follows. (1) Radioactivity frightens because its effects were mostly publicized by the bombs on Hiroshima and Nagasaki, it is associated with cancer, it is very easy to detect by radiation measuring devices, yet we do not perceive it: nature bas not found any advantage in inventine biolaeical sensors for radioactivitv. ,. we are ahle rather accurately to calculate and descrihe its effects, even at very low doses (althuugh low.dcae effects arestill m d~spute),whrch ellows us t o publrsh alarming frgures abuur the number of cancers that will develop a s a consequence of large-scale,low-level contaminations. (2) The origin and nature of rodioaetiuity. This point should be developed in accordance with the scientific level of the audience. In most cases, it is sufficient to recall that it is a nuclear phenomenon and that there are three main types of radiation: alpha, beta, and gamma rays. More important is to quote that these rays are energy vehicles and that this enerev is transmitted to the livine tissues expored to the radiations, upsetting the replicative organization of cells, leading to rancer, abortion, or generic damage. (3) Units to be remembered when deoline with rodiooetiuitv the herquerel (Bq)unit of activity: I disintegration per second, the gray ( G y ) unit of dose; 1 pule depurited per kilo,~r.ram of exposed matter, the sievert (Sv),related to the gray but takes also into account the specific danger of a given type of radiation toward living tissues. This point is frequently confused or ienored. (4) Theeffects of radiations on human beings. Thisis of course a very important part of the lecture, and I am convinced it is more interesting to start from acute effects, as they are easier to understand (in spite of their appalling context): Increasine death rate at doses >4-5 Sv (whole bodv): This is the moment o; remember that such high doses are encountered in catasrrophic et,ents only. In the rase of Chernobyl, about 30 persons died from acute exposure. In all the history of peaceful applications of nuclear energy, this was by far the worst incident to be recorded. Lesions at a few tenths to a few sieverts: This may also be considered to be a high dose level. Lesions appear on skin, for examole. and their "eravitv - is directlv linked to the dose receivei. it is easv, to make cam oar is an^ with burns induced hv ~, hear: in bothcaaes,radistionorhear, thegravity ofthelesionsis linked to the flux olenerm deposited in the tissues. The same example helps show that there must be a threshold below which no effect is observable because too low fluxes of energy allow tissues to resist attack or to recover. Random or stochastic effects from zero (?) to a few tenths of a sievert: The possible consequences are cancer and genetic effects. The main differencewith the oreviouslv described effects is that, from all exposed persons,only a reduced percentage ail1 suffer from cancer or, if able LO procreate, will give birth to defective offspring. The only effect of thedose is to increase the percentage of victims, not the gravity of the harm. (5) The incidence of cancers. Once again, it is not sufficient to declare that radioactivity induces cancers and genetic defects; we have to quantify the effect and to compare it with the natural incidence. It is generally agreed upon that among I00 persons receivingadose of I Su (a highdose), one cancer is likelyto be induced in the coming years. This effect has now to be compared with the
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Materlal To Be Used Lectures are more convincing if simple equipment is used to illustrate different points. In this case, I think a small GM counter (with a beeper) is essential to demonstrate the uhiquitous aspect of radioactivity. An old watch with a radiumpainted dial helps to demonstrate that a few decades ago the daneers of radioactivitv were not recoenized as thev are today. A small thermol&ninescent dosimeter shows that determinine doses a t work laces is a relativelv easv task. I consider i t most important to have an aerosol sampler which is ahle to filter air particles a t a rate of a t least 20 m3 h-'. This will show that indoor particulates are radioactive. I ~ersonallvuse a simple domestic vacuum cleaner placed butside the lecture room and connected to a stainless steel filter holder (from Sartorius Gravikon). Ordinary laboratory filters are used (Whatman 41; 16 cm diameter). I n such conditions, a reasonably powerful vacuum cleaner is ahle to filter up to 40 m3 of air during a one-hour lecture, which is usually sufficient to give a significant response under the GM counter nrouided the room is not ventilated bv outdoor air. At the v>ry beginning of the lecture, I show-the filter oaner that is intended tocollect the oarticulates we are eoine breathe during the forthcoming hbur. It is installed on t h l filter holder and the vacuum cleaner is turned on.
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natural incidence of cancers among our populations which amounts to 20-255, depending on the country. It is astonishing to see how people generally grossly overestimate cancer risk from radiations; this is probably due to alarming figures transmitted without any comment by newspapers. After the Chernobyl event, predictions were made about the possible occurrence of thousands of cancers in Europe, but most of these statements failed to mention the natural incidence of cancer, which has to he expressed in tens of millions. (6) The incidence of genetic effects. Genetic effects are even more difficult to document because, so far, no genetic damage has ever been ohserved in human beings as a consequence of radiation. Extrapolations from experiments made on other living systems suggest that we might expect 3000 to 4000 anomalies per million births per sievert. This seems enormous hut, once again, it has to be compared with a natural incidence of about 100,000 anomalies per million births, and most of these anomalies are almost undetectable or of minor gravity. U p t o now, we have merely provided measurements about radioactivity a n d its consequences. T h e second part of the lecture intends t o make comparisons: comparisons between t h e levels of natural and artificial radiations comparisons between the risks induced by t h e radiations in our environment and from artificial sources, either in normal use or in accidental conditions. (1) A~tifieiolsourcesof radiations. Human technology bas developed different sources of ionizing radiations to which we all are likely to be exposed. To sum up the general situation briefly, we receive a total of 200-1000 pSv/a, depending mainly on medical sources. Chernohyl was a significant but not alarming contribution to artificial sources (50 pSv in 1986). (2) Natural sources of radiations. Nature is the main contributor to the overall dose we receive, delivering a total of 2000-4000 pSv each year, and this Largely exceeds artificial sources. Radon, via its daughter radionuelides, mainly (214Pband %I4Bi), is responsible for the main dose delivered to house-dwelling organisms, and the intensity of irradiation largely depends on the materials used for building, on the nature of underlying ground and on the quality of house insulation. Energy-saving programs stimulated drastic reductions of house ventilation; we are now able to estimate that these programs did much to enhance radiation doses to the general population. Atthis stage of t h e lecture, we can seize the opportunity t o demonstrate t h e presence of radioactivity in the air. T h e vacuum cleaner is turned off, and the filter paper is p u t in contact with the GM counter. T h e excess activity is easily detected by t h e audience. I must say that, in general, this discovery of t h e presence of radioactivity in the air we
breathe exerts a very profound impression on most of the people. (3) Risks of cancer from artificial and natural sources. This demonstration of the ubiquity of natural radioactivity introduces the com~arisonof risks from artificial and natural sources of radiations. A; natural sources contribute about 80%of the average dose, we loricallv ,deduce that artifieiallv induced cancers should be onefifrh as irnporrnnr na the naturally induced. Huurver, ~f we remrmlrer the induction rate of cancer by radiatiuns , l l aupplen~entary casesper gray), weare brought to estimate that an average one-year dose (artificial +natural radiations = say 2.5 mSv) could induce 2.5 10W%cancers in an average population: and, again, this has to be compared with the natural incidence of 20 to 25%!The main causes of cancer have to he found elsewhere.
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We have insisted on the natural character of radioactivity; i t is a comoonent of our environment. and it is evident t h a t life is adapted t o the doses deliveredto every organism on earth. We are aware of the fact that. in normal circumstances, artificial radiations are b u t a fraction of the natural level we all live with. Medical diagnostic and therapy contribute most in dose budget t o thegeneral populati&. Thia deliberate irradiation of human beinzs comes under the heading of a n ethical choice: the balance between costs and benefits of these medical techniques. There are innumerable instances where balances are made in our everyday life. Smoking, drinking alcoholic beverages, and riding motor vehicles are deliberate choices t h a t expose individuals t o the greatest risks in developed countries and that, however, are considered totallv acceotahle. I am con\.inced that unravelling the mysteries of radioactivit!. to the oublic and tostudents in simoleand clear terms coulb greatl; enhance the general acceptability of its applications because the risks involved are largelv - .outweinhed - bv the benefits.
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Suaaested Readlna
United Nations. "Radiation-Doses, Effeeta. Risks": United Nations Environment Pm. gramme: Nairobi. Kenya, 1985. Pachin. E. "Nuclear Radiation: Risks and Bonefita", Monographs on Science. Technology and S ~ i e t no. v 2: Oxford Science Public., 1986. i s e '-comparisonof risk r e s u ~ n gfrom human sxietr ~ ~ a ~ ~dea~sdi~proteetion. activities": C-R. Xthregianal CongressofInternationalRadiationProtretionAssoeiation: Avignon. France. 1982. T ~ Y I O T ,L. S. '-some innuenee on protenionstandards end the 1980 Sievert lecture", Heolth Phys. I$RO,39,851-874. Tubisna,M. "Les bases biologiquer de isradioprokefion",publishedin Vigilonce,Franse, no. hors seris, mai 1983.
Call for Papers-Semon National Undergraduate Research Symposium The 13th Annual Waldo Semon Chemistry Symposium, will be held at Kent State University on Monday, April 8, 1991. A major focus of this event, which is co-sponsored by Kent State University and BFGoodrieh, will be the Semon National Undergraduate Research Symposium, held for the fourth consecutive year. Students at colleges and universities anywhere in the United States are invited tosuhmit apaper describing their undergraduate research work. This should be limited to 10 double-spaced, typed pages with any number of additional figures, tables, and references. The paper should be written entirely by the student and should be structured in a format similar to that of a full page published in an American Chemical Society journal (i.e., abstract, introduction, results and discussion, conclusion, experimental section, and references). A panelof judges will select six finalists, who will be invited to present short (20-25 minute) seminars describingtheir research work at the symposium.The student presenting the best paper will receive a $2,00Oprize,with $200 going to each of the five remaining speakers. All travel arrangements will he made at no expense to the participants. Students who are interested in participating in the 1991Semon National Undergraduate Research Symposium should write for further details to: Paul Sampson, Chair, Semon Chemistry Symposium Committee, Department of Chemistry, Kent State University, Kent, OH 44242, or call (216) 672-2032. Letters of intent to submit papers should arrive in Kent no later than December 19,1990. The deadline for receipt of papers is March 1,1991.
Volume 67
Number 9
September 1990
737
