Landfill Gas Found to Have High Levels of Highly Toxic Dimethyl Form of Mercury
By Janet Raloff •
December 5, 2001
Science News Vol. 160, No. 1, July 7, 2001
Mercury, a nerve poison, is a major ingredient in many products-from
thermometers and fluorescent bulbs to batteries and old latex paint. A
new study finds that landfill disposal of such products can chemically alter the mercury in them, not only rendering it more toxic but also fostering its release into the air.
Although even mercury in its elemental form is toxic, its most poisonous embodiment is methyl mercury, the result of a chemical modification by bacteria (SN: 3/9/91, p. 152). The finding of such a process in landfills underscores the importance of ensuring that mercury doesn't enter the municipal-waste stream, says study leader Steve E. Lindberg of Oak Ridge, TN, National Laboratory.
The decomposition of interred landfill wastes creates methane. Some
landfill managers burn the gas in flares as it exits pipes atop the
waste field. Most managers, however, merely vent the gas-and any
contaminants it may carry-into the air.
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.
Lindberg, S.E., et al. 2001. Methylated mercury species in municipal
Waste landfill gas sampled in Florida, USA. Atmospheric Environment
Raloff, J. 2000. Methylmercury's toxic toll. Science News 158(July
29):77. 1994. More illuminating statistics on mercury. Science News
______. 1994. Mercurial airs: Tallying who's to blame. Science News
______. 1991. Mercurial risks from acid's reign. Science News 139(March
U.S. Environmental Protection Agency, Office of Water. 1999. Mercury
update: Impact on fish advisories. Fact Sheet. September. Available at
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
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:
John W.M. Rudd Fisheries and Oceans Canada 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 35155
From Science News, Vol. 160, No. 1, July 7, 2001, p. 4.
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