Is a toxic mix more deadly than its parts?
March 22, 1997
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Where do estrogenic toxins come from? How could combinations of estrogenic toxins be more harmful than its parts? What could be causing the discrepency between the synergy studies? Could a better cellular test be developed to look for synergy? If the Tulane study proves correct, should the EPA lower its acceptable levels for estrogenic toxins by a factor of 1600? If synergy is proven to exist, how should EPA testing of toxins be changed? Additional comments
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December 23, 1996
Fred de Sam Lazaro looks at Minnesota's mutant frogs.
January 1, 1997
Paul Solman reviews the year in genetics.
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The Online NewsHour's editors asks:
What could be the causing discrepancy between the Tulane group's results and some of the work by researchers at Texas A&M and the EPA's National Health and Environmental Effects Research Laboratory? What additional work is needed that could resolve this controversy?
Prof. Porter of the University of Wisconsin responds:
I think we could simply accept the fact that different types of tests on cell cultures and living organisms might give different results. This is not unusual for cell based tests to give different results than whole organisms. Cell cultures can be used for screening, but only for that purpose. Whole organism tests are a much better forum for asking whether mixtures might have biological effects. We could expend a lot of resources and money to find out exactly why a certain mix affects cell cultures, but not whole organisms, or we could expend our resources finding out whether commonly co-occurring mixtures can affect intact organisms. It seems to me that is a better use of our scarce resources.
Dr. Lynn Goldman of the EPA responds:
Some of the discrepancy results from the fact that no investigations have actually attempted to replicate the Tulane study exactly. Rather than using the same in vitro test systems used by the Tulane researchers, other investigators have attempted to expand the hypothesis to mammalian systems. None, of the studies reported to date have used the identical yeast-estrogen system or mammalian cell lines used in the Tulane studies. At present it remains unknown if the 1600-fold synergy reported by the Tulane research group can be reproduced using the same cell lines. This uncertainty is likely to be resolved in the near future as the Tulane researchers have provided their yeast strain to other laboratories. Even if the specific synergy hypothesis raised by the Tulane study cannot be reproduced, it does not negate the possibility of synergy through other mechanisms. As such, the Tulane study remains important in that it raised awareness of the synergy to the forefront of scientific investigation.