Making Cigarettes Safe?
Although the major cancer-causing substance in cigarette tar has not yetbeen identified, so much is now known about it that smoking could berendered relatively harmless—without waiting for the substance to beisolated. This reassurance came last week from the man who, since hisstudent days, has been busy amassing proof that heavy, long-continuedcigarette smoking is the main cause of the recent dramatic increase inlung cancer: Dr. Ernest L. Wynder, 34, of Manhattan's Sloan-KetteringInstitute.
Dr. Wynder told the American Association for Cancer Research, meeting in Chicago, that the villain is not present in tobacco leaves in theirnatural, unburned state. His research team proved this by extractingtar from cigarette tobacco without burning it: the resulting substanceproduced virtually no cancers when painted on the backs of mice. Butbatches of the same tobacco were burned at varying temperatures, andthe tars extracted. Tar from the lower-temperature-burning ranges produced few or no cancers. From 800° to 880° C. the numberof cancers increased sharply. Conclusion: evidently, the cancer-causingagent is the result of high-temperature combustion.
Tentative Conclusion. Could the original substance from which the canceragent is formed be pinned down and removed from the tobacco? Wynder &Co. closed in on a natural waxy substance that is known to coat thetobacco leaf. In the wax are "aliphatic hydrocarbons.'' which, burnedat high temperatures, produce "polycyclic hydrocarbons," and these inturn can cause cancer.
Working with the University of Toronto's Chemist George Wright, theresearchers washed tobacco in hot hexane, which dissolves the wax. Theyextracted the wax and burned it alone. The resulting tar proved to beat least ten times as cancer-potent as ordinary tar from whole tobacco:in five months all mice painted with a 5% solution from tests at 880°had papillomas , and 27% had full-blown cancer.The tar from the wax contained all the cancer agents now known to existin small amounts in cigarette tar, but Dr. Wynder doubts that thesesubstances are the only cause of the lung-cancer increase, suspectsthere are others in the tar. One tentative conclusion: dewax thetobacco to make it less harmful. Dr. Wynder did not say what cigaretteswould taste like if made from dewaxed tobacco.
Other Possibilities. Wynder also saw hope for making the cigarette saferalong several other lines. One is to reduce the temperature at which acigarette burns, now in the 800°-880° C. range, to a heat now shown tobe relatively harmless—around 767.° the average temperature at whichtobacco burns in a pipe.
Another way would be to develop a filter that would remove at least 40%of the tar. Present filters, said Dr. Wynder. remove too little of thetar—and they let the cancer agent pass as freely as the rest of thesmoke. Dr. Wynder's willingness to settle for a 40% filter is based onstatistics: among two-pack-a-day smokers the incidence of lung cancerevery year is 278 per 100,000; for men who smoke only half a pack to apack for the same 20 years or more, the incidence is only 61. A 40%filter would bring most men's tar intake down to the equivalent of wellunder a pack a day.
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