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Everyday Carcinogens: Acting for Prevention
in the Face of Scientific Uncertainty
by Dr. Sandra Steingraber
Author, "Living Downstream"
Adolescence is another period of vulnerability. We don't know very much about adolescent boys, and there is a lot more to be learned, but we do know something about breast development in adolescent girls. And in my capacity as a cancer activist, I serve on President Clinton's National Action Plan on Breast Cancer, and we've been looking at how the breast bud develops during puberty in girls from the age of about ten to thirteen. And we feel that we have enough information in looking at the data, to advocate for a change in the way girls receive X-rays. When adolescent girls go in for dental X-rays or sprained ankles, there's enough scatter of the X-ray to the chest wall that we feel we need to shield those developing breasts with some kind of lead apron, anytime a girl receives any kind of X-rays, whether or not it's to her chest wall or any other place because the developing breast is undergoing rapid mitotic division and the DNA is more vulnerable to the effects of carcinogens during that time then they would be to say a forty year old woman or sixty year old woman or even a five year old girl whose breasts have not started to develop.
| "...if we were to make the world safe for twelve year old girls and six week old embryos, it would require a big change in the way we regulate cancer-causing chemicals." |
So the fact that we enter and leave these windows of vulnerability turns out to be really important because the question becomes then, where and how do we regulate toxic chemicals? Do we do it to protect the adolescent girl, do we regulate them tightly enough so that six week old embryos are also sufficiently protected? Well, if we believe in equal protection under the law then the answer would have to be yes. Because we all start off as six week old embryos, we all go through puberty at some point and we all need to have sufficient protection from cancer-causing chemicals during that time. But if we were to make the world safe for twelve year old girls and six week old embryos, it would require a big change in the way we regulate cancer-causing chemicals.
The last line of evidence I might have mentioned about comes from animals. This was actually an amazing revelation for me because I'm trained as a wildlife biologist and until I sat down and did the research for 'Living Downstream', I didn't know that there was a parallel epidemic among cancer in animals that in very many ways tracks what we are seeing in humans. We know this because in the US we have a registry for tumors in animals and when I was studying this it was held in the Smithsonian Institute, it's now held at George Washington University, and these document fish with liver tumours, whales with bladder cancer, salamanders with cancer, snakes, frogs, etc. And invariably, when you see high levels of cancer in populations of animals it's associated with some kind of known environmental contamination. When you look at the same species of animals in pristine places you don't see these kind of cancers. So for example in Canada, there are epidemic levels of cancer among the beluga whales in the St. Lawrence river, but in Canada's more pristine estuaries you don't see any cancer at all among the belugas. Animals are in some ways better to study when raising questions about cancer in the environment than humans because wild animals don't drink, smoke or hold stressful jobs. They don't have bad diets. So you can't blame lifestyle factors on the ascendant rise of cancer among fish.
Again, my argument to you today is that even though we don't have absolute proof in the way that the scientific community feels comfortable talking about proof, we in the scientific community set the burden of proof very very high. Statistically, we won't say we found anything of significance unless we're 95 per cent sure that we have something and that's because science does not like to say we've discovered something unless we're extraordinarily sure. So the wheels of scientific proof-making grind slowly, slowly onward. And I believe in that process .. it's important. And yet if we're in the middle of an epidemic of cancer, and not all cancers have reached epidemic proportions, but certainly those of us who are mothers who are looking at the data on childhood cancers, would say this is very frightening to see that more children get cancer every year than the year before. We have more two year olds with brain tumors than we ever have.
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| "We also know that if you look at the map of non-Hodgkin's across North America, it tends to cluster where we use a lot of herbicides." |
When you look at those data, maybe you don't want a 95 per cent certainty that a certain chemical causes a childhood brain tumor before you say .. you know what, all that I want to know is there's a possibility that this chemical is going to cause cancer in kids before we expose everybody to it. So there are a couple of different kinds of conservatism. There's the conservatism of the scientific community and then there's the conservatism of parents who want to protect their kids. After all, mothers don't need to know with 95 per cent certainty that their kid is going to be hit by a car when they tell the child, don't play in the street. They just need to know that there's a reasonable danger to that child and we need to take precautionary action to prevent people out of harm's way. Those are two different kinds of conservatism. And there's a healthy debate to be had between science on the one hand and the kind of things our grandmothers said, like 'better safe then sorry', on the other hand.
How does this apply to non-Hodgkin's lymphoma? Well, I think that there's pretty good evidence showing us that non-Hodgkin's has a link to certain kinds of weed killers. And we can't say this with 95 per cent certainty and there is no one study that shows us this. But here's how it works when you look at the weight of the evidence across disciplinary lines in biology.
We've already looked at the cancer registry data and established that we've seen this very swift ascending lines of non-Hodgkin's and we know that it's not related to heredity, it doesn't appear to be related to any lifestyle factors that we know about and it's not just affecting the elderly. An increase is seen in all age-groups. So we know that with certainty. We also know that if you look at the map of non-Hodgkin's across North America, it tends to cluster where we use a lot of herbicides.
Now, we can also look at the occupational literature and ask, are there any professions in which non-Hodgkin's lymphoma is rising even more swiftly then its rising in the general population. When you do this several things jump out at you. This is part of what I talk about in, I think it's chapter four of 'Living Downstream'. One group that has excess rates of non-Hodgkin's is farmers. Another group is Vietnam veterans who were exposed to Agent Orange, which is a weed killer, when they fought the war in Indochina. Another group is pesticide applicators, people who spray lawns, fumigate grain storage bins, things like that. The last group is golf course supervisors. What all those groups have in common are exposures to pesticides. And again, that's not absolute proof but we're starting to see a consistent story emerging here.
| "... And it turns out that pesticide applicators (like non-hodgkin's patients) also have high levels of this strange mutation (DNA inversion) in the cells of their blood. |
Now let's look at the animal data. Are there any animals that we know that get non-Hodgkin's? Well, as it turns out that dogs get canine non-Hodgkin's and it's a very similar disease to that of humans. And the incidence of canine non-Hodgkin's is also rising when you look at veterinary records. Moreover, when you look closer at those records it turns out that dogs whose owners who use weed killers in the backyard are twice as likely to have canine non-Hodgkin's then dogs whose owners who don't use lawn chemicals.
Finally we can look at the genetic data and ask, are there any mutations, any genetic mutations that are associated with non-Hodgkin's? And it turns out there is one. It's called a DNA inversion, which is a very rare event. It's caused when the chromosome actually breaks in half, flips upside down and reattaches itself. And this particular one associated with NHL is on chromosome thirteen or seventeen, I'm not sure which, it's one of the middle chromosomes but it's very specific and it's very easy to identify. My colleague Vincent Gary at University of Minnesota has done some of this work. And he was able to document that non-Hodgkin's patients have high frequencies, tend to have high frequencies of this mutation. So he asked, are there any other groups out there that have this mutation? And it turns out that pesticide applicators also have high levels of this strange mutation in the cells of their blood. So again, even though non of these studies by themselves are the absolute proof that we in the scientific community would feel comfortable with, the weight of the evidence from all of them together is starting to tell a consistent story.
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