Air Date: Week of December 11, 1998
Steve Curwood talks with John Brock who is a section chief at the Centers for Disease Control in Atlanta. Dr. Brock co- authored a study published in the current issue of the British medical journal "The Lancet" which links the banned pesticide Dieldrin to a doubling in breast cancer for women exposed to the compound.
CURWOOD: This is Living on Earth. I'm Steve Curwood. The current issue of the British medical journal the Lancet details new evidence of the link between synthetic chemicals and increased risk of cancer. This time the culprit is Dieldrin, the pesticide that was bAnned in the US in the 1980s. The study looked at blood serum gathered from nearly 8,000 women in Denmark in 1976. It found that any exposure to Dieldrin increased the risk of having breast cancer, and that those with the highest exposure to Dieldrin were twice as likely to have breast cancer. John Brock is a section chief at the Centers for Disease Control in Atlanta and a coauthor of the study. He says even though Dieldrin was bAnned, it is still very much with us today.
BROCK: Dieldrin is still, was still used for termite control until about 1985. So it's in the basement of most homes right now, actually, throughout the Southeast. So it's still in our environment. The second thing is, Dieldrin's lifetime in the soil and how long it lasts in the soil, the half-life, is about 60 years as long as it's not exposed to the sun. So it's still in our soil, too. These persistent compounds, these persistent organochlorine compounds, last for years and years and years and years. So they're going to be with us for some time in our food supply, in our homes, and all around us.
CURWOOD: There have been a number of previous studies that have shown no correlation between exposure to pesticides of the organochlorine group that include Dieldrin. And now there's your study, which shows a pretty strong correlation. Why do you suppose the difference?
BROCK: There's 2 reasons. One reason is, most of the other studies have not measured Dieldrin. Most studies only focused on DDT, metabolites, and PCBs. We do a screen for many different compounds, and Dieldrin was one of those compounds. The second reason is, most of the other breast cancer studies had been done in the United States, where the levels of Dieldrin exposure are in fact lower. So you would expect that the correlation would be harder to find.
CURWOOD: How many chemicals did you screen for from the serums that were offered to you by the Danes?
BROCK: About 48 chemicals.
CURWOOD: And Dieldrin was the one that lit up the lights.
BROCK: Right. None of the others really showed any significant effect.
CURWOOD: Well, tell me, what kind of -- what level of exposure was necessary to increase one's risk of breast cancer?
BROCK: The levels of Dieldrin in these women were a little bit higher, in general, than we find in the United States. But they were not occupational exposures. These were background levels of exposures on the order of half a part per billion.
CURWOOD: This sounds like a tiny amount to be exposed to.
BROCK: Right. It is a tiny amount, it is a very small amount of Dieldrin.
CURWOOD: How many Danish women percentage-wise would have this much in their bodies?
BROCK: Well, in the total group that we looked at, about 70% of Danish women would have levels around this.
CURWOOD: So, 70% of Danish women would have enough Dieldrin in their bodies to place them at an increased risk of breast cancer.
BROCK: If this study is duplicated, and we prove these findings in other studies and we back this finding up, Dieldrin is a cause for concern.
CURWOOD: These are quite interesting numbers. What's the percentage of women in the United States who have the level of Dieldrin in their bodies comparable to the Danish women who had the problem?
BROCK: If you go back to the 70s where these blood samples were originally taken in Denmark and do a comparison to women in the 70s in this country, the levels back then were about 10 to 20%. Today I'm not exactly sure what the levels are because we're in the middle of doing that analysis now.
CURWOOD: Potentially that's a lot of cancer cases.
BROCK: If this finding is true, and holds up under repeated studies, I'd say yes, it is a significant finding.
CURWOOD: John Brock, I'm wondering, how much should results like this be a cause of concern to women?
BROCK: I think it's a concern, but it's not absolute proof. When we started looking at smoking and lung cancer, when CDC started first looking at that, the first couple of studies weren't given that much weight. It wasn't until the studies overwhelmingly showed the same result in different groups of people, in different countries, and then you have a case. Then you have a case of evidence where you say okay, now we've got a public health issue here that really needs to be addressed immediately. With breast cancer and Dieldrin I think that this is just the first study, and I think that we need to keep doing these kinds of studies until we have a case against Dieldrin. If it in fact is the bad actor, or one of the bad actors in breast cancer.
CURWOOD: John Brock is a section chief and research chemist at the National Center for Environmental Health at the Centers for Disease Control in Atlanta. Thank you, sir.
BROCK: Thank you.
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