Mercury in fish may be less toxic
But researchers, critics not advocating end to warnings,
By Susanne Quick
Milwaukee Journal Sentinel
TNT, when ignited, is deadly. But when it's laced with
nails, its power to destroy multiplies.
The same goes for different forms of methylmercury,
says an international team of researchers today in the
journal Science. Some varieties cause more bodily harm
than others. And according to their research, the form
of mercury in fish may not be the nail-laced powder keg
people thought it was. It may be less toxic.
Indeed, it's because of mercury's links to neural damage
in children that both state and federal health agencies
have advised people to avoid eating certain kinds of fish
from some lakes and bodies of water since the 1970s.
The researchers behind the new study believe their findings
may cause policy-makers to reconsider the strict standards.
Others, however, are not so sure. Henry Anderson, chief
medical officer for the Wisconsin Division of Public Health,
said that even if the team's findings pan out, state consumption
advisories wouldn't change.
"We test for the total amount of methylmercury already
in people's blood" and create advisories based on
that, he said. "This finding could have implications
for risk-based" assessment studies - but not on the
How toxic is it?
For the first time, biophysicists using an advanced form
of X-ray technology were able to examine the physical
and chemical makeup of mercury found in fish. And they
discovered it was different from the variety used in laboratory
experiments and less toxic.
"But you're not going to see me eating a thick steak
of swordfish any time soon," said Graham George,
a biophysicist at the University of Saskatchewan, in Saskatoon,
Canada, and an author of the paper. "Mercury is toxic,"
no matter what the variety.
He said more studies were needed to examine the physical
properties of mercury in humans. And until then, people
should remain cautious when eating contaminated fish.
But David Petering, professor of chemistry at the University
of Wisconsin-Milwaukee, said at best, there was nothing
new in this study - and at worst, it was misleading.
"Sixty thousand children a year will suffer some
effects of methylmercury exposure" from eating fish,
said Petering, citing a 2000 study from the National Academy
of Sciences. "And the effects are irreversible."
But George says his work is novel - and that "cautious
optimism" should be used in interpreting his results.
Using a technique called X-ray absorption spectroscopy,
George and his colleagues from Stanford University and
the University of Sydney, Australia, "fingerprinted"
mercury found in samples of fish bought at the grocery
Then they compared the prints to a portfolio of known
methylmercury compounds, and identified their suspect
as methylmercury cysteine.
This form - with its sulfur-packed caboose - is not the
one usually studied in laboratory settings. The lab variety,
George said, is methylmercury chloride.
And chloride, said George, is super adept at slipping
across membranes and staying intact in watery solutions
- dangerous abilities for a toxic compound. This may make
methylmercury appear more toxic than it actually is in
"People have used methylmercury chloride to model
the toxic properties of fish because they don't know what's
on mercury. And now that we know what's on mercury in
fish tissue, we can better investigate its toxic properties,"
said George, who plans on testing the methylmercury in
fish-eating mammals next.
"This is a landmark study," said Thomas Clarkson,
professor of toxicology at Rochester University, N.Y.,
referring to George's work. "I don't want to detract
But he concurred with UWM's Petering that the discovery
of cysteine on methylmercury was expected.
"I'd agree that we have known that for a while,"
he said, but George's study has confirmed it. "And
The thing is, methylmercury is highly attracted to sulfur,
Petering said. So, even if it enters a fish (or human)
carrying a chloride, it'll soon shed it for what it wants.
And because sulfur-laden cysteine is a common amino acid
in animals, it's long been assumed that's what methylmercury
did - irrespective of the form it entered in - said Petering.
"If this is about what people use in labs,"
he said, well, that's irrelevant. "Scientists care
about what form it takes going in and out of cells."
And that, he said, is the form with sulfur.