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Landfills Make Mercury More Toxic

Janet Raloff

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.



While open landfills (above) may expose wildlife directly to poisonous mercury, closed landfills can vent tainted gases through pipes (below).



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 (Tenn.) 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.



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, NJ


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.

U.S. Food and Drug Administration. 2001. FDA announces advisory on methyl mercury in fish. January 12. Available at

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

John W.M. Rudd
Fisheries and Oceans Canda
Environmental Science Division
501 University Crescent
Winnipeg, Manitoba R3T 2N6

Edward Swain
Minnesota Pollution Control Agency
Environmental Outcomes Division
520 Lafayette Road
St. Paul, MN 55155

From Science News, Volume 160, No. 1, July 7, 2001, p. 4.