Food and Nutrition of Children
It is concluded from experiments on mice that the road dust stirred up by vehicles is the most dangerous source of carcinogenic agents, and road tar is one of the factors responsible for an increase in cancer of the lung.
Abstract
The internal combustion engineand the modern roadswhich it has made necessary have been charged with much evil, including responsibility for an increase in cancer of the lung. Argyll Campbell' concludes from experiments on mice that the road dust stirred up by vehicles is the most dangerous source of carcinogenic agents. He used mice in which the: incidence of spontaneous -lung tumours was about -8 per cent. The -incidence rose to 80 per cent. in some experiments when the mice were repeatedly exposed to atmospheres containing road dusts. Tar extracted from the dusts of tarred roads-was painted on the skin of mice and produced skin cancers. The carcinogenic agent thus demonstrated was not, in Campbell's view, the sole cause of lung tumours, since these were increased, though less conspicuously, by-dusts fromwhich the tar had been extracted. Kling, Samssonow, and -Heros' painted mice with a road tar and observed skin cancers and a high incidence of lung tumours. They detected 1: 2-benzpyrene in the tar by its fluorescence spectrum. Later3 they reported that road materials absorbed benzpyrene and held it firmly, and they attributed the activity of Campbell's extracteddusts to the incomplete removal of benzpyrene. Their conclusion is that road tar is one of the factors responsible for an increase in cancer of the lung; it contains the-undoubtedly carcinogenic substance 1: 2-benzpyrene, which should be removed. This conclusion was vigorously contested in the discussion at the Acackmie de Medecine of Paris, and subsequently Guglielminetti4 denied that benzpyrene was -present in road tar in the quantities alleged, that an increase in lung cancer coincided with the introduction 'of tar for road surfacing, or that road tar was concerned in the aetiology of cancer of the lung in man. Previously, Kennaway and Kennaway' had found no evidence that the tarring -of roads had affected the incidence of cancer of the lung among the general population. The disagreement will not be resolved without laborious clinical and statistical inquiry, but one point at issue-the relevance of experiments on mice-is ripe for present discussion. Lung tumours are common in mice and are relatively beniign. Murphy and Sturm' first recorded an increased incidence as the result of repeated applications of tar to the skin, the sites of application being' varied in each mouse so as to avoid the production of skin cancer. The mode of action of the tar was disputed. Recent papers by Shimkin7 and Magnus' contain references to later investigations and record new results. Shimkin injected 1:2: 5: 6-dibenzanthracene or methylcholanthrene intratracheally into mice of a pure strain having an incidence of spontaneous lung tumours of 20 per cent. Lung tumours developed in 90 per cent. of-the mice, but Shimkin stated that intratracheal injection was not so convenient or efficacious as intravenous injections, -and he mentioned reports of increased inci-