Two years ago, Lindberg's team found methyl
mercury in the water vapor that condensed out of
the gas emanating from a Florida landfill.
Concentrations were at least 100 times those
typically seen in water. The finding made sense,
Lindberg recalls: In wetlands, researchers had
previously identified certain bacteria that
methylate natural, inorganic mercury derived from
minerals. This same family of microbes resides in
landfills.
However, methyl mercury comes in two
forms—mono- and dimethyl-mercury—with the
latter being the more toxic. To probe which form
is made in landfills, Lindberg and his coworkers
collected gases destined for flaring. In the
August Atmospheric Environment, they report
finding some 50 nanograms of dimethyl mercury per
cubic meter of landfill gas.
That "is higher, by a factor of 30 or 40,
than concentrations of total mercury in ambient
air," Lindberg notes, and it's at least 1,000
times that of any dimethyl-mercury concentration
ever recorded in open air. His team also detected
lower concentrations of the less volatile
mono-methyl mercury in the landfill gas.
Although chemists had detected methyl mercury
in air and rain, "nobody had been able to
demonstrate where it comes from," notes John
W.M. Rudd of the Winnipeg (Manitoba) Freshwater
Institute, part of Canada's Department of
Fisheries and Oceans. The new study offers
"the first real evidence that landfills might
be a major source," he says.
Some 60,000 U.S. children are born each year
with developmental impairments triggered by fetal
exposure to methyl mercury, usually as a result of
their moms having eaten tainted fish (SN: 7/29/00,
p. 77). "If it doesn't get methylated,
mercury doesn't get into fish," observes
Edward Swain of the Minnesota Pollution Control
Agency in St. Paul.
To limit the rain of mercury from human
activities, regulators have focused on curbing
emissions of inorganic mercury from coal burning.
However, Lindberg notes, although chemists assumed
that mercury could become methylated in the air,
they couldn't show it.
Now, Swain posits, a "shift in
paradigms" may be in order. He says that
sending mercury-containing wastes to landfills may
essentially be spoon-feeding copious amounts of
the toxicant to methylating bacteria, which then
cough the injurious forms into air.
The new findings point to the need to inventory
emissions by landfills—especially the older
ones, which hold the richest stores of
mercury-tainted wastes—says Frank D'Itri of
Michigan State University's Institute of Water
Research in East Lansing.
Lindberg plans to embark on such an inventory.
He says that the new data also suggest a need for
technologies to capture methyl mercury from
landfills before it can enter the atmosphere.
Letters:
I am writing to correct a
significant inaccuracy in your recent article
"Landfills make mercury more toxic." As
a member of the National Research Council's
committee that produced the report you cite, I
feel obligated to correct your statement,
attributed to that report: "Some 60,000 U.S.
children are born with developmental impairments
triggered by fetal exposure to methyl mercury,
usually as a result of their moms having eaten
tainted fish."
The report actually states
that "over 60,000 newborns annually might be
at risk for adverse neurodevelopmental effects
from in utero exposure to MeHg (methyl
mercury)."
The intent of that statement
was to convey that 60,000 children are born each
year with in utero exposures that exceed the
committee's estimate of a safe level of exposure.
This does not, however, mean that these children
will necessarily have impairments.
I do not, of course, intend
this clarification to imply that methylmercury
exposure is not a serious concern or that
governments should not take steps to reduce
mercury emissions to the environment. They should.
However, the distinction
between being at risk for an adverse effect and
actually having the adverse effect is critical to
current notions of risk assessment and risk
management.
Alan H. Stern
University of Medicine and Dentistry of New
Jersey-
Robert Wood Johnson Medical School
New Brunswick, N.J.
References:
Lindberg, S.E., et al.
2001. Methylated mercury species in municipal
waste landfill gas sampled in Florida, USA. Atmospheric
Environment 35(August):4011.
Further Readings:
Raloff, J. 2000.
Methylmercury's toxic toll. Science News
158(July 29):77.
______. 1994. More
illuminating statistics on mercury. Science
News 145(Feb. 26):142.
______. 1994. Mercurial airs:
Tallying who's to blame. Science News
145(Feb. 19):119.
______. 1991. Mercurial risks
from acid's reign. Science News 139(March
9):152.
U.S. Environmental Protection
Agency, Office of Water. 1999. Mercury update:
Impact on fish advisories. Fact Sheet. September.
Available at http://www.epa.gov/ost/fish/mercury.html.
U.S. Food and Drug
Administration. 2001. FDA announces advisory on
methyl mercury in fish. January 12. Available at http://www.cfsan.fda.gov/~lrd/tphgfish.html.
Links to mercury-related EPA
Web sites can be found at http://minerals.usgs.gov/mercury/epalinks.html.
Sources:
Frank D'Itri
Institute of Water Research
115 Manly Miles Building
Michigan State University
East Lansing, MI 48823
Steve Lindberg
Environmental Sciences Division
Oak Ridge National Laboratory
P.O. Box 2008
Oak Ridge, TN 37831-6038
Web site: http://www.esd.ornl.gov/people/lindberg/lindberg.html.
John W.M. Rudd
Fisheries and Oceans Canda
Environmental Science Division
501 University Crescent
Winnipeg, Manitoba R3T 2N6
Canada
Edward Swain
Minnesota Pollution Control Agency
Environmental Outcomes Division
520 Lafayette Road
St. Paul, MN 55155
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