Yesterday I sketched out some of my reasons for doubting that smoking caused lung cancer, and a couple of my alternative hypotheses. It drew quite a few comments. And it’s in response to one of these that I’m going to write some more about one of them: the radioactive fall-out hypothesis.
One of the strengths of the fall-out hypothesis is that it’s fairly well known that small amounts of radioactive material cause cancers. I’ve read that when mice are painted with radioactive material, they invariably develop cancer. It wasn’t just 10% or 20% of them. It was the whole lot.
There are a variety of fall-out hypotheses. One of these is that radioactive fall-out lands on food crops, and finds its way into humans that way. Same if it lands on tobacco plants.
But the fallout hypothesis that I was turning over a few years back was that, between about 1945 annd 1965, there was a constant rain of fall-out coming down everywhere in the Northern hemisphere all day every day. It only stopped with the 1963 Test Ban treaty which confined nuclear weapons testing underground. But even then the Chinese and the French carried on testing. There are some maps available online showing the geographic distribution and density. The upper map below is cesium-137 deposition (bq/m2) across the USA, with red 8000 bq/m2, and blue 0 bq/m2. The lower map is lung, trachea, bronchus and pleura cancer mortality, 1970-94 (hat-tip to Fredrik in the comments, from Lauren Colby).
Fredrik Eich in the comments under yesterday’s post said that the problem he had with this theory was that men got lung cancer more often than women, “and I don’t see alpha emitting radio nuclides as being that sexist!” And I remembered that I’d thought about this too, and come up with what seemed a plausible explanation for the cancer difference between the sexes.
The explanation was that the interiors of houses were protected from falling radioactive particles in exactly the same way that they were protected from falling rain. It ran off the roof into the gutters. So if you spent most of your time indoors you were less likely to get sprinkled with fall-out than if you spent most of your time outdoors. And you’d be correspondingly less likely to get fall-out-induced lung cancer from inhaling airborne radioactive particles.
On this hypothesis, it would be people working outdoors much of their lives, like farmers and labourers and builders and the like who would be more likely to develop lung cancer and other forms of cancer, because they were being sprinkled with radioactive material falling from the sky. And these people are almost always men. There are very few women labourers or builders or farmers, because it’s very much men’s work.
In addition, back in the 40s, 50s, and 60s, most women were married houswives. They didn’t have jobs. They stayed at home and looked after babies and children, and they cooked and cleaned and washed. Occasionally they’d go out and do some shopping, but that was very often a short trip to a local shop. These women spent most of their time indoors. So they were pretty safe from the ever-falling radioactive particles coming down from the sky.
Their breadwinner husbands, by contrast, were usually out the door by 8am to catch a bus or train to their place of work. Even if they worked in sheltered offices or factories, they’d spend an hour or two every day standing by bus stops, waiting on open platforms, or riding bicycles, with the drizzle of fall-out landing on them. Furthermore, the nature of the work of some of these office workers would have obliged them to spend periods of time outside. Architects would have to visit building sites, van drivers would deliver goods, etc. The degree of exposure of men to the outside environment would have increased as their social status decreased, with labourers digging up roads having the highest exposure, and Whitehall mandarins in their offices having the lowest exposure. And even the Whitehall mandarins would very often have a higher exposure to the external environment than women who went out shopping once a week for groceries.
So, it’s not that radioactive fall-out was sexist. It was that men almost always spent more time outside than women did, and got covered with more fall-out.
A further objection to the fall-out hypothesis might be that it was fairly well known that lung cancer was more common in cities than in the countryside. How could the fall-out hypothesis explain that? The answer is: in precisely the same way that it just explained how people who spent their time inside houses were safer than people who spent most of their time outside them.
Cities are made up of impervious materials like tiles and tarmac and concrete and steel. Water mostly runs off. And so does fall-out. Both remain on the surface in cities. But in the countryside the ground is absorbent. Rainwater sinks into it, and percolates away underground. And so does fall-out. Or at least the smallest particles of fall-out. It doesn’t remain on the surface. And this means that in cities there’s likely to be build-up of radioactive fall-out sitting on roofs and in gutters and on the street below. Much of this will gradually be washed away by rainfall into storm sewers, but in dry weather the fall-out will be blowing around from one roof to another, and from one road to another. And this won’t be happening so much out in the country. Hence the impermeable cities will have a much higher density fo fall-out build up in them than the permeable grass-covered earth around them. Cities will be more radio-actively ‘hot’ than the countryside. And so there’ll be more cancer in cities than in the countryside.
Cleanliness will also have an effect. Just like rainwater can be brought into houses on wet shoes or umbrellas or coats, so fall-out can come into houses in exactly the same way. The water eventually evaporates, but the fall-out is likely to stay on the floor. Unless the floor is regularly swept, or better still, vacuumed, it may be inhaled or otherwise ingested.
The same applies to personal hygiene. If you don’t wash, your skin is likely to get covered in fall-out, and stay that way. But if you regularly wash your whole body, and your hair, and your clothes, most of the fall-out will be washed out. It also helps if you buy new clothes quite regularly.
I believe that the incidence of cancer in women is becoming much more like that of men than it was 50 or 60 years ago. And that would be explained by women ceasing to be housewives and instead going out to work every day just like their husbands. This increases their exposure to the fallout-laden external environment. So also will exposure be increased by wearing fewer or lighter clothes – the result of changing fashions.
The same sort of reasoning might be used to explain differences between different countries or cultures. There seems to be a lower incidence of cancer in Mediterranean countries like Spain and Greece. How might that be explained using the fall-out hypothesis? It may just come down to how long people spend outside. And in hot countries, people tend to stay in the shade. And being in the shade very often means being indoors. Cultural differences (e.g. the incidence of housewives) would also affect this. Even differences in architectural styles would affect it. So also would the degree of economic activity. Economic growth means more roads, trains, power lines, drains, and more labourers working outside.building these roads and houses and factories. It means more people going out to work every day. Greece and Spain were, until recently, relatively economically backward. You’d have to look at the culture of each country separately.
The peak of the rain of fall-out would have been from the late 40s through to the late 60s. After that, the fall-out would have dwindled away as atmospheric testing stopped. But because many radioactive materials have half-lives of hundreds of years there’s probably quite a lot of it about still, particularly in cities. When was the last time London or Birmingham had a good wash?
One thing that the fall-out hypothesis can’t explain, however, is the increasing incidence of lung cancer prior to the first nuclear bomb tests in 1945, because there wasn’t any fall-out before then. Lung cancer incidence started rising in 1920, or even slightly earlier. But this increase might have been caused by a different sort of ‘fall-out’. Marie Curie first isolated radium in about 1900, and was unaware of the danger of radioactive materials to human tissues. And shortly afterwards there began to appear radium soaps and even radium drinks, as well as radium clock hands and numbers. Radium was pretty much being sold by the pound in grocers’ shops, wrapped in greaseproof paper. So radioactive material in considerable quantities was percolating through society. And so that was what was causing the rising incidence of cancer. All these products are gone now, but when I was in my teens in about 1960, I had what was probably one of the last of the radioactive wristwatches. It glowed in the dark like a bunch of fireflies. I’ve never seen a watch like it since.
So that’s the fall-out hypothesis more or less as I dreamt it up a few years ago.
The constituents of radioactive fall-out are probably pretty well known. Some constituents will have short half-lives, and some long ones. We’re living now in the trailing edge of a wave of radioactive material that has been passing through our societies for the past 100 years, peaking in the 1950s and 60s. If the half-lives of the constituents of fall-out are very long, then the trailing edge of the wave will decay slowly, and there’ll be plenty more cancer for everybody for a century or more. The incidence of all kinds of cancers will probably plateau, but not fall much. The likelihood of anyone getting cancer would vary with their age. The longer someone lives, the greater the likelihood of fall-out lodging on their skin, or in their lungs or throat or stomach. But even young children would be quite likely to develop cancers, if they lived in a fall-out hot spot.
Counter-measures against it would be cleanliness, and particularly cleanliness of city streets, which would need not just to be swept, but washed and scrubbed. Roofs should also be cleaned and washed. And walls as well. Houses should be regularly vacuumed (because sweeping is likely to disperse fall-out). Skin and hair and clothes should be regularly washed.
Anyway it’s just a hypothesis. Quite likely there isn’t a shred of truth in it.