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www.caps.20m.com Canadians Against Pesticides |
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PAGE 2... Everyday Carcinogens: Acting for Prevention in the Face of Scientific Uncertainty by Dr. Sandra Steingraber Author, "Living Downstream" A second line of evidence I want to mention comes from computer mapping and this project takes these same cancer registry data and instead of displaying them over time so that you can look at time trends, it displays their distribution over space. And when you do this the maps that result clearly show that cancer is not a random tragedy.
Let's paint for a moment the picture of what breast cancer looks like in North America. So if you can picture the North American continent in your mind's eye and you wanted to draw the hotspots of where breast cancer tends to distribute itself .. where do you see the big excesses in breast cancer. What you would do is colour in red from Maine down to Washington, DC all along the Great Lakes Basin, including the area where you are now sitting, and the lower part of the Mississippi River from Baton Rouge down to Louisiana and also the San Francisco bay area in California. Those areas, except for the California cluster, also represent the places in the US and Canada where we see the most bladder and colon cancer. And again the Great Lake Basin is one the places where we see not only breast but colon and bladder cancers, highest in North America in those places. And of course, the eastern seaboard and the Great Lakes region and the lower part of the Mississippi River are the areas where historically are the most intensely industrialized areas. Again these maps don't tell us that there's a causal connection between industry and cancer. It's a correlation and correlations sometimes are causative and sometimes there's not. But we need to pay attention to them and it does indicate a possible hypothesis that we need to investigate further with other kinds of studies. Now let's draw the picture for non-Hodgkin's lymphoma. Again, conjure up in your mind's eye a map of North America. You would colour in red the Great Plains areas, particularly Kansas and Nebraska. I haven't looked at the data to see whether they go up into Manitoba and Saskatchewan or not. I know the US data better here. But in the United States it's Kansas, Nebraska, Iowa and a little bit in a shaded pink, Illinois and Wisconsin. And of course, this is where we have the highest intensity of pesticide use in grain agriculture in those areas. And again, these correlations are not necessarily causative but they are provocative. A third line of evidence comes from our own bodies. We know that a whole kaleidoscope of chemicals linked to cancer exists inside of all of us. These include pesticide residues, industrial solvents, electrical fluids called PCBs, dry-cleaning fluids are found in the blood and breath of anyone living in the urban area, and they also include the unintentional by-products of garbage incineration and, of course, these are the very famous dioxins and furans, which unfortunately play such an important role in the recent history of Hamilton, Ontario. These chemicals are found in various places in our bodies. They don't all go to one place, depending on the specific biochemistry of each one, they partition themselves in different organs and places in the body. I'm happy to answer questions about what goes where but in general where we've seen these chemicals turn up are breast milk, body fat, blood serum, semen, umbilical chords, hair, placentas and even in the fluid surrounding human eggs. So even before conception we know that we have exposure to chemicals that in the laboratory are linked with cancer. We do not know with certainty what the cumulative effect of all these multiple exposures is. All we can say is we know we have chemicals linked to cancer, both known carcinogens and suspected carcinogens, inside all the bodies of people who live in North America. But we are not in the dark completely, even though we don't know all the interactive effects, everything about multiple exposures. There are some areas of this very new and confusing science that are becoming clearer and clearer. For example, we are honing in on the various biological mechanisms by which these chemicals seem to be working their ill-effects. The old scientific thinking was that in order to cause cancer a chemical had to mutate your genes, it had to cause some kind of damage on your chromosomes. Chromosomes are the part of your body that's made of DNA and the genes lie along the chromosomes like beads on a chain. And its damage to those beads that we call mutations and we know that mutations are necessary for cancer to form. We think about eight to ten mutations are actually required before a cell is put on the pathway to cancer formation. So the old thinking was, well, if something didn't cause mutation then it probably didn't cause cancer. |
Well, the new thinking is showing us that there are a whole set of chemicals called endocrine disruptors that actually don't break our chromosomes, don't bother the genes, don't cause lesions on your DNA but they are able to in some way mimic or interfere with our hormones. And what the hormones are, are chemical messengers sent from one part of your body to another that by definition get inside cells and turn on and turn off certain genes. They're messengers that tell our genes to do something. So chemicals that have the ability to mimic hormones, that actually get inside our cells, they are kind of like toxic trespassers, and instead of damaging the genes they flip a switch during a time that that switch is not supposed to be flipped. And if it's a gene that's regulating cell division then you can get runaway cell growth which of course is one of the hallmark symptoms of cancer formation. Now probably these hormone disruptors can't cause cancer all by themselves, they probably need to work together with a mutating chemical or a chemical like estrogen, that's found in a woman's own body. But even though they may play the role of supporting actor rather than the prime mover in cancer, it may contribute to how swiftly the cancer develops, whether the cancer metastasizes, whether you're diagnosed at the age of forty instead of at the age of sixty, etc. So the new science is showing us that we can't just look at chemicals that cause mutations, we need to look at this whole other set of chemicals that seem to be interfering with hormones.
Another part of the science that is getting clearer and clearer has to do with the timing of exposure. And that is turning out to be critical. The old thinking was, and you probably all heard this phrase somewhere along the line, the dose makes the poison. That's actually a paradigm of toxicology that was coined by Paracelsus, a medieval monk who lived in Switzerland I think in the 1300s. And he recognized that, for example, a large amount of salt could kill a person but a small amount of salt might be very beneficial. And so the way we in Canada and the US have regulated toxic chemicals is presupposed on this idea that the dose makes the poison. So the thought is if we can regulate carcinogens to a low enough level below some kind of threshold that we can all continue to have exposures but these exposures will be negligible and they won't hurt us. But the new science is really mounting a challenge to that supposition. Because it turns out that each of us go through various what we call windows of vulnerability during our lifespan, during which time we are exquisitely sensitive to the effects of small amounts of chemicals that can set us up for future cancers, even though larger amounts at some other time when we're not so vulnerable might not have an effect. So in other words, we're not all 150 pound white men, which is the basis on which we historically have regulated a lot of toxic chemicals and we are forced now by the new science to revisit that kind of regulation. We know for a fact that prenatal life represents a window of vulnerability. A six week old fetus whose entire development is being orchestrated by hormones is exquisitely sensitive to the tiniest amount for example of dioxin. And since I know that in Hamilton, Ontario you are very interested in dioxin, let me spend a minute to talk about some of the new studies on that. When laboratory rats are exposed to dioxins in utero something very usual happens. If you take a mother rat who is pregnant and expose her at a particular point in her pregnancy to the tiniest level of dioxin that we can measure on our instruments, the baby rats are born and they look perfectly healthy and then grow up into adults who are perfectly healthy. But when you then expose those adult rats who were exposed previously to dioxin in utero, when you expose the adults to a carcinogen when they're old rats they go on to develop cancer. Whereas, if you expose adult rats to that same carcinogen and yet those rats have not been exposed prenatally to dioxin they don't go on to develop cancer. So somehow dioxin exposure in the womb serves as a magnifying glass for the harmful effects of later exposures to other chemicals. And if you expose adults to dioxin, they also don't have a harmful effect. So it's something about the timing of exposure before birth that's really critical. |
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