Scientists are worried about the effects
of Mercury at lower level than previously
thought dangerous. I wonder what effect
this has on the Amalgam debate..
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New York Times November 2, 1999
New Efforts to Uncover the Dangers of
Mercury
By ROBERT A. SAAR
Most people think of mercury
as the shiny liquid metal in
thermometers. But it has other forms,
and it is a less visible, and very toxic,
kind -- methylmercury -- that is
troubling scientists, environmentalists
and government officials.
Methylmercury is formed from the
mercury discharged into the air by
coal-burning power plants,
incinerators, mining and other
sources. The mercury rains down
onto the land and leaches into
waterways; there, having been
converted by bacteria into
methylmercury, it collects in the fatty
tissues of fish and the animals that
prey on them.
Its concentration rises at each step
up the cooking.net">food chain until it is consumed
by people.
While most industrial uses of mercury are declining,
concentrations are nevertheless increasing in the
environment and in the cooking.net">food chain. Airborne
mercury is estimated to be three to six times the
level it was in pre-industrial times.
The toxicity of methylmercury at low concentrations is
a matter of intense debate. As a result, scientists
and government officials are making new
efforts to determine how much mercury is safe to
consume and whether new limits on power-plant emissions
are needed.
The National Academy of Sciences has established a committee to
investigate the mercury toxicity issue, but its work is difficult.
Recent studies of the effects of low-level mercury exposure, primarily
from eating contaminated fish, have produced differing results. One
showed neurological damage; the other did not. The committee's study,
sponsored by the Environmental Protection Agency, began last
December and is scheduled for completion next June.
Dr. Robert Goyer, the panel's chairman, says its top priority is to
determine the effects of prenatal mercury exposure. "Methylmercury,
the
type of mercury found in fish people eat, kills nerve cells because it
is
transported readily across the cell membranes," said Dr. Goyer, a
pathologist who is professor emeritus at the University of Western
Ontario.
"The bottom line for the N.A.S. study is determining the minimum
amount
of mercury that will affect the most sensitive member of our
population,
the unborn child.
The current data from different studies are not consistent."
The panel's conclusions could have big implications for the
coal-burning
plants of the electric power industry. The Environmental Protection
Agency estimates that it would cost about $2 billion a year to control
mercury emissions from those plants; Congress has required the
environmental agency to wait for the National Academy of Sciences'
study before proposing additional mercury regulations for power
plants.
Death and illness from mercury poisoning have been documented since
the 16th century in Europe. The expression "mad as a hatter" came into
the language because hat makers were poisoned by mercury salts used
to make felt for fancy hats. They were well known for their symptoms:
shaking, stumbling and muttering to themselves. And in the 1960's and
70's, consumption of cooking.net">food heavily contaminated with methylmercury
resulted in death or serious illness to thousands of people in Japan
and
Iraq.
But subtle, mostly neurological, effects of low doses are now emerging
as
the long-term legacy of mercury. Slower reflexes, reduced coordination
and poorer vision are evident in people ingesting small amounts of
mercury in fish. But the effects are difficult to measure and despite
decades of study, experts disagree on the levels of mercury that are
safe
in air, water and food.
"It is a frustrating issue," said Dr. David C.
Bellinger, an associate professor of
neurology at the Harvard Medical School
and member of the National Academy of
Sciences committee. "With mercury, we
have only a few major studies." He said
more mercury studies were needed to form
a better foundation for regulatory change.
Dr. Donna Mergler, a professor of
neurophysiology at the University of
Quebec at Montreal, says that in many
respects, the situation with mercury is
similar to what it was years ago for lead.
"Why take lead out of gasoline and paint?"
she said.
"No one was getting sick or writhing on the
ground. But lead did lower the I.Q. of kids.
Subtle effects for toxins like lead and mercury are sometimes
difficult to
see in the individual, but can be seen in a group portrait where we
compare the functioning of groups of people exposed to different
levels."
But in some respects, mercury is a more serious contaminant than lead.
Because mercury can exist in vapor form, it can spread around the
globe far more easily than lead. Also, "mercury accumulates more
efficiently than lead in the aquatic cooking.net">food chain, especially in larger
predatory fish," said Dr. William H. Farland, director of E.P.A.'s
National Center for Environmental Assessment.
Even minute additions of mercury to a lake can substantially increase
the
amount in the fish people eat.
Regional effects of mercury have been observed by teams of Canadian
and Brazilian researchers working along the Amazon River since 1994.
They have concluded that the small amounts of mercury naturally
occurring in local soils can substantially raise the concentration of
methylmercury in fish when the soil erodes into the river after
clear-cutting of the adjacent forests. Neurological testing has shown
that
local people have been affected.
"Coordination and vision tests showed a shift to lower performance at
higher levels of mercury exposure from fish eating," said Dr. Mergler,
one of the researchers working in Brazil.
"This lower level of performance makes the people less able to do
things,
which is important in a world which is expecting them to develop."
Programs are under way to reduce mercury exposure there by
encouraging consumption of fish species with lower mercury levels.
Fish consumption was also examined in two major studies under way
since the late 1980's. One, in the Seychelles, in the Indian Ocean,
found
that general performance on intelligence tests was not affected by
exposure to methylmercury; the other, in the Faroe Islands, northwest
of
Scotland, found deficits in memory, attention and language.
The studies differed in many respects, including eating patterns in
pregnancy, ethnic or genetic makeup, and testing methodology. They are
now under review by the national academy's panel.
Mercury enters the body in a number of
ways, including diet, dental fillings,
pharmaceuticals and contact with mercury
metal or its compounds.
But it is fish -- "brain food" -- that is the
major dietary source of methylmercury to
humans.
Nonetheless, the cooking.net">food and Drug Administration continues to recommend
consumption of as much as 1 kilogram (2.2 pounds) of fish and
shellfish a
week and has not changed the mercury level it considers safe: 1 part
per
million in seafood. (Another government agency, the Agency for Toxic
Substances and Disease Registry in the Centers for Disease Control and
Prevention, has a similar recommendation; under it, a 150-pound person
could safely eat four ounces of canned tuna a day.) The top 10 seafood
species, making up 80 percent of the commercial market, all average
well
below that.
Shark and swordfish, both top predator fish, may have mercury
concentrations above 1 part per million, and the F.D.A. continues to
recommend no more than one weekly serving of these two fish for most
people, and no more than one serving a month for pregnant or nursing
women, or those who may become pregnant.
The push to lower overall exposure to mercury has continued on many
fronts.
In June, the E.P.A. announced that fluorescent bulbs, which contain
mercury, could now be recycled to keep them out of waste dumps. On
Sept. 14, the National Wildlife Federation released a study blaming
coal-burning power plants for more than half of excess mercury in rain
in
several Midwestern cities.
On Sept. 24, the E.P.A. announced a plan to severely restrict the
direct
discharge of mercury and other chemicals that accumulate in fish in
the
Great Lakes.
Despite all this activity, it will be difficult to gain full
protection of human
health and a comprehensive understanding of mercury's effects in the
human body and the environment. Dr. Farland said the Academy of
Sciences panel would have more information than the C.D.C. did in
making its recommendations, but he added:
"They will still not have complete information.
Over all, we are looking at what to do to avoid adding more mercury to
the environment and how controls on mercury sources may improve
human heath."
Copyright 1999 The New York Times Company
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