An intriguing new study published recently on Environmental Health News challenges the long-held assumption on which all regulatory toxicology testing is based, and poses new questions about what -- and how much -- of certain toxic substances merit "OK" exposure.
Toxicology tests are usually performed by giving subjects (usually rodents) high doses of a substance and monitoring the biological response. The assumption has long been that what these high doses do to the subject indicates what a lower dose could do. Using high doses is generally faster, more reliable, and cheaper.
But the new research indicates that with some pollutants, drugs, and natural substances, the effects of the toxic substance vary according to dose -- meaning that the results of high doses might mean absolutely nothing when it comes figuring out the effects of lower levels of exposure.
Take, for example, the pair of rats featured prominently in a photo accompanying the study. While in-utero exposure to 100 parts per billion of the estrogenic drug diethylstilbestrol (DES) makes for scrawny adult mice, exposure to just one part per billion causes grotesque obesity, one study found.
Does this mean higher doses of toxics are better for us? Not likely. But it does mean that since most regulation is based on apparently false assumptions, we might have a whole bunch of health standards that are too weak.
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Comments
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caniscandida Posted 12:29 am
13 May 2007
Here is some information, with links, from the Humane Society of the United States:
http://hsus.org/animals_in_research/animal_testing/
Chickens are our cousins!
So are other sensitive animals!
Enough is enough!
No more factory farms!
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Green Granny Posted 12:29 am
13 May 2007
Is any level of any poison, including those that affect the endocrine system, acceptable?
"We must be the change we wish to see in the world." -- Mahatma Ghandi
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Quinn Posted 2:40 pm
13 May 2007
My point is that it doesn't matter if the effects vary with the dose. The fact that rats are obese with a low dose of DES and scrawny with a high dose is completely irrelevant. In determining levels of safe exposure to a chemical, any observable effect is taken into account. Scientists look for the threshold at which effects start and normality ceases. Anything beyond that point is interesting and intriguing, but not relevant to regulatory toxicology.
We're not "all doomed." Enough with the whistle blowing for the sake of whistle blowing.
As for the question of whether any level of poison is acceptable, first define poison. Any substance at a large enough dose is poisonous including (believe it or not) water, caffeine, and sugar. Granted the dose would have to be enormous, but they still could be fatal.
That said, some chemicals are more toxic than others. But as long as people are around, there will be toxins around to affect us. To declare that any level of toxin is unacceptable is completely unrealistic. Since everything is toxic at a large enough dose, the best we can do is find out what dose is safe and try to keep it below that.
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