[1] 13w Lung Cancer Induced in Hamsters by Low Doses of Alpha Radiation from Polonium-210

[1] 80w Lung cancers have been induced in 9 to 53 percent ofhamsters given multiple intratracheal instillations ofpolonium-210 in amounts yielding lifetime exposures of 15 to 300 rads to the lungs. Cigarette smokers have previously been estimated to receive 20 rads to areas of the bronchial epithelium from deposited polonium-210. Thisfinding thus supports the hypothesis that alpha radiation resulting from the polonium-210 or lead-210 present in cigarette smoke may be a significant causative factor in human lung cancer.Polonium-210 is a naturally occurring,

[1] 157w All of the frank tumors found in the present study arose in the peripheral lung. These tumors were frequently multicentric, and showed both epidermoid and adeno- matous features. We have therefore classified them as combined epidermoid and adenocarcinoma; their characteristics are described in detail elsewhere (7). They are readily transplantable (7). In addition, however, the lungs from some animals, particularly from the low-exposure groups in which the tumor induction times were very long, showed focal areas of marked bronchiolar epithelial hyperplasia with cellular atypia and metaplasia. Since these le- sions did not show the invasive characteristics associated with the frank carcinomas, they have been classified separately as "borderline malignancies" (Table 1). Neither such focal changes, nor any frank lung tumors, were found in 94 control hamsters which received either no treat- ment, or 15 weekly instillations of carrier particles alone. This lack of spontaneous lung cancer in Syrian hamsters is consistent with the findings of others (6).

[2] 81w The results of experiments in which hamsters were given 15 weekly instillations of 3 mg of carrier particles, each contain- ing 0.25 to 5.0 nc of 210po, are tabulated in Table 1. Lifetime radiation doses averaged over the whole lungs were determined in parallel experiments in which the total radioactivity retained in the lungs was mea- sured at various times during and after the course of instillations, and the energy deposited per gram of wet lung was con- verted to rads.

[3] 178w After administration on ferric oxide carrier particles, 2o(po is retained in the lung in a distinctly nonhomogeneous pattern, associated primarily with visible hematite aggregates in macrophages surrounding al- veolar ducts (8, 9). It could be argued that the carcinogenic effect of 210Po under these conditions of administration is due to the high localized radiation fields arising from these "hot spots"; in this context, the aver- age lung dose might have little biologic meaning. Following intratracheal adminis- tration alone in saline (no carrier particles), 20Po0 is distributed much more ho- mogeneously throughout the bronchiolar- alveolar region (9). The results of two ex- periments in which hamsters were given weekly instillations of 210Po alone in saline are tabulated in Table 2. That the alpha tracks were uniformly distributed throughout the lung parenchyma in these animals was confirmed by dry mount autoradiography of freeze-dried frozen sections. Clearly, the data in Tables I and 2 indicate that at the lower doses there was no marked difference in the carcinogenic ef- fect of 210po when the radioactivity was uniformly deposited throughout the lung

[4] 87w parenchyma as compared to when it was present in a patchy distribution such as oc- curred following administration on parti- cles. These results are consistent with those of earlier experiments utilizing higher doses (7,9). With similar nanocurie amounts per instillation, 210po adminis- tered in saline (Table 2) yielded a some- what lower radiation dose than did 2opo administered on particles (Table 1). This is because the soluble 210po was more effi- ciently cleared from the lung in the early time periods, particularly by way of the bloodstream.

[5] 191w Doses in the range of several thousand to 105 rads have generally been necessary for the induction of experimental lung can- cer by beta or gamma radiation (5). In two other studies, however, lung tumors have been induced by relatively low doses of al- pha radiation. Yuile et al. (10) found pri- mary lung tumors (mostly epidermoid carcinomas) in 3 to 13 percent of rats which received 71 to 538 rads from 2"Po inhaled in a sodium chloride aerosol. These results were complicated somewhat by the presence of acute and chronic pulmonary infection which was endemic in their rat colony. Recently, Sanders (11) has re- ported inducing lung cancer (primarily bronchioloalveolar carcinomas) in 6.6 to 25 percent of rats receiving 9 to 375 rads from inhalation of an aerosol of "soluble" 238Pu (238Pu emits alpha radiation similar to that of 210Po). In his lowest exposure group, bronchioloalveolar carcinomas were found in 2 of 30 rats which received only'9 rads to the lungs from an initial lung bur- den of 5.0 nc of inhaled 238Pu. One lung tumor, a large cell undifferentiated car- cinoma, was found among 92 control (un- treated) rats.

[6] 129w In these studies, as in ours, the estimated lifetime radiation dose was averaged over the entire lung volume. Local doses to small tissue volumes where the radioactivity may preferentially accumulate or concentrate, such as occurs in bronchial epithelium of cigarette smokers' lungs (3), may have been significantly higher. This would certainly be the case following intra- tracheal administration of 210po on ferric oxide carrier particles. Following adminis- tration of 2o0po in saline, however, there was no autoradiographic evidence of in- homogeneities in the microdistribution of radiation dose throughout the bronchiolar- alveolar region of the lung (the target tis- sue) (9). Local tissue doses would thus be expected to approach the whole lung aver- age. Such would also appear to be the case for the inhalation of soluble 238Pu (11).

[7] 52w From these considerations, it appears reasonable to conclude that the local alpha radiation doses associated with the induc- tion of lung cancer in some experimental animals may be within the same general 738 order of magnitude as those received by cigarette smokers to small areas of the bronchial epithelium from deposited 210po.

[8] 81w The total amount of 210po administered to our lowest exposure group in Table 1 (3.75 x 103 pc) is roughly one-fifth the amount inhaled by a heavy cigarette smoker (two packs per day) during 25 years (2,12). In addition, not only does cigarette smoke contain small amounts of many chemical carcinogens which may be acting syner- gistically with the alpha radiation, but the respiratory tract is also unusually vulner- able to infection which may enhance the carcinogenic effect of radiation (13).

[1] 169w alpha-emitting radionuclide of the ura- nium decay series which is present in trace amounts in most plants and foodstuffs as well as in human tissues (1). Radford and Hunt (2) proposed that alpha radiation from 2Iopo, which is volatilized at the temperature of a burning cigarette and thus carried off in the smoke, might be a causa- tive factor in the increased incidence of lung cancer among cigarette smokers. It was subsequently shown (3) that smokers' lungs contain increased accumulations of 2"Po, particularly within the bronchial epi- thelium in the region of segmental bifurcations. Recently, Martell (4) has reported that 2"'Pb (parent isotope of 2""Po with a physical half-life of 22 years) is also present in cigarette smoke in the form of insoluble particles of high specific activity which derive from the combustion of tri- chomes in the tobacco leaf. The insoluble 2'0Pb particles deposited and retained in the lung would decay by beta emission to 2'0Po particles, and thus act as a contin- uing source of alpha radiation.

[2] 103w From measurements of 2oPo in pulmonary tissues (3), it was calculated that smokers receive on the order of 20 rads over a 25-year period to localized areas of the bronchial epithelium from deposited 2""Po. On the basis of previous studies in experimental animals, it has generally been assumed that much higher radiation doses are necessary to induce a significant incidence of lung cancer (5). The present in- vestigation was undertaken to assess specifically the carcinogenicity to the lung of low levels of 210Po alpha radiation. A significant incidence of lung cancer has been found following whole lung exposures as low as 15 rads.

[3] 158w Syrian golden hamsters were chosen for this study, as they have been shown pre- viously to be very resistant to chronic pul- monary infections, and to have a zero incidence of spontaneous lung tumors (6). Details concerning the maintenance of ani- mals, preparation of 2'(Po suspension, instillation technique, and scoring of tumors have been described (7). The animals were followed for their natural lifetimes, and were killed when moribund. Polonium-210 was adsorbed onto ferric oxide carrier particles (98 percent with a mean diameter of less than 0.75 um), and suspended in sa- line; 0.2 ml of the saline suspension con- taining 3 mg of ferric oxide was instilled into the tracheas of lightly anesthetized hamsters. In some experiments, 20Po was administered in saline alone without carrier particles. The major radiation dose fol- lowing these methods of administration is to the bronchiolar-alveolar region of the lung (8), the region where nearly all of the induced lung tumors arise (7).

[4] 75w These results tend to support the hy- pothesis that 210po or 2'0Pb in cigarette smoke may be a significant factor in the initiation of lung cancer in smokers. They are, moreover, components which are well characterized, do not contribute to "fla- vor," and should be relatively easy to re- move from cigarette smoke (14). JOHN B. LITTLE, ANN R. KENNEDY ROBERT B. MCGANDY Laboratory of Radiobiology, Department ofPhysiology, Harvard University School ofPublic Health, Boston, Massachusetts

[5] 103w 2,3,7,8-Tetrachlorodibenzodioxin (TC- DD) is a particularly toxic compound; the oral LD,O (lethal dose to 50 percent of a test group) for many animal species is in the range of micrograms per kilogram (1). It is a very stable compound, with a half- life in soil of about 1 year (2). It is only gradually excreted in the feces and urine of mammals, and its toxic effects suggest that it accumulates in body tissue after recur- rent exposure (1, 3). The known toxic effects of TCDD include anorexia, severe weight loss, hepatotoxicity, hepatoporphy- ria, vascular lesions, chloracne, gastric ulcers, teratogenicity, and delayed death (1).

[6] 97w Chlorinated dibenzodioxins include a large number of compounds, some ex- tremely toxic and others essentially non- toxic. They have no known use, but occur as contaminants in technical products such as tri-, tetra-, and pentachlorophenol and a number of other related compounds (4). The most toxic of the chlorinated dibenzodioxins, TCDD has been associated with several industrial accidents in which the subsequent cleanup of the area con- taminated by this compound created major problems (5). This report describes the first recognized incident in which significant poisoning resulted from the improper dis- posal of waste residues containing TCDD.

[7] 217w Waste oil sludge is frequently used to control dust on riding arenas and dirt roads. On 26 May 1971, a salvage oil company sprayed an arena for this purpose on a horse breeding farm in eastern Missouri. Three days after the oil sludge spraying, sparrows and other birds that normally populated the barn rafters were found dead on the arena floor. Over the next several weeks, hundreds of birds, several cats and dogs, and numerous rodents died after being exposed to the arena (6). Of the 125 horses on the farm at the time of spraying, 85 were exercised for varying periods within the arena. Sixty-two of those ex- posed became ill, and 48 died. The first horse death occurred on 20 June, and de- spite removal of soil from the arena in Oc- tober 1971 and April 1972, horses contin- ued to die as late as January 1974. All of SCIENCE, VOL. 188 Tetrachlorodibenzodioxin: An Accidental Poisoning Episode in Horse Arenas Abstract. Tetrachlorodibenzodioxin was identified as the apparent cause of an out- break of poisoning in humans, horses, and other animals. Exposure was related to the spraying ofcontaminated waste oil on riding arenas for dust control. The contamination resultedfrom the improper disposal ofa toxic industrial waste. The pathologic effects and chemical identification of tetrachlorodibenzodioxin are described.