Nature Science Update Article: Dangerous levels of toxins miscalculated

Charles Miller rellim at tulane.edu
Tue Feb 18 11:47:03 EST 2003

This new article in Nature is sure to generate some discussion. Below is a


Chuck Miller
"They're always havin' a good time down on the bayou..."
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Dr. Charles A. Miller III
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(504)585-6942, rellim at tulane.edu
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Dangerous levels of toxins miscalculated
Potential pollutants and poisons may be beneficial in low doses.
13 February 2003 


We may be putting too much effort into cleaning our enviroments.

The levels at which potentially toxic substances such as mercury and lead
are classified as dangerous may have been miscalculated, two US scientists
are warning. Risk assessments and regulations on safe limits for these
substances in medicine and the environment may have to be rethought, they

There are safe levels below which potential pollutants and poisons may
actually be beneficial, say Edward Calabrese and Linda Baldwin of the
University of Massachusetts in Amherst. For the past 30 years,
cancer-causing chemicals and X-rays have been viewed largely as dangerous
whatever their level.

"The field of toxicology has made a terrible blunder," says Calabrese. "A
lot of high-powered people need to take the time to explore this."

For example, dioxins, which are industrial by-products that at certain doses
can cause cancer, can actually reduce tumour growth in some species.
Similarly, small amounts of the toxic trace metal cadmium can promote plant

"What we call 'toxic chemicals' is a misnomer," says cell biologist and UK
government advisor Anthony Trewavas from Edinburgh University. "Mild
chemical stress is beneficial."

Having identified over 5,000 similar examples, Calabrese and Baldwin are
among a growing number of researchers who feel that the hazardous nature of
toxic substances has been overstated. The levels used in studies are not
comparable to those normally experienced by humans, Calabrese says. "This
provides an interesting challenge for the clinical and pharmaceutical
industries as they develop new medicines."

Britain's Medicines Control Agency (MCA) is more cautious. "The point of
toxicological testing is to determine the drug exposure at which undesired
effects are observed," a spokesperson said, adding that the new criticisms
are, "unlikely to change the way in which the MCA or other regulatory
agencies conduct product risk-benefit analysis."

The debate also raises the question of how clean our environment really
needs to be. Some argue that billions of dollars are being wasted ridding
the world of substances that are dubbed 'hazardous', when low levels could
actually be a good thing.

"We don't need to spend large amounts of money on removing chemicals from
the environment," says Trewavas. "Food contains lots of natural chemicals
that are as damaging as synthetics. We consume lots of these all the time
without harm. The public need re-educating in this."

But convincing people that 'safest' is a more meaningful description of risk
than 'safe' and 'dangerous' is notoriously difficult.


1.    Calabrese, E.J. & Baldwin, L.A. Toxicology rethinks its central
belief. Nature, 421, 691 - 321, (2003). |Article|

© Nature News Service / Macmillan Magazines Ltd 2003


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