In-use mercury sensors moved one step closer to extinction when the National Institute of Standards and Technology began collaborating with the U.S. Environmental Protection Agency's efforts to phase out the devices.

NIST researcher Dawn Cross calibrates a mercury thermometer using the icepoint of water as a reference. Last month, NIST ceased to offer the calibration services for mercury thermometers as part of its efforts to reduce the amount of mercury in the environment.
Photo courtesy of NIST


Those mercury-filled thermometers parents depended on for their sick kids, long have been off the market in the United States. With industry, though, there still is at least one U.S. mercury-thermometer manufacturer, and thousands of the sensors still working away at hundreds of plants and laboratories nationwide.

Those in-use sensors moved one step closer to extinction when the National Institute of Standards and Technology began collaborating with the U.S. Environmental Protection Agency's efforts to phase out the devices.

NIST announced last month that it no longer will provide calibration services for mercury thermometers, something it has been doing since it opened its doors in 1901. Closing the program is part of a larger effort by the EPA and other professional standards, environmental and industry groups to end the use of mercury thermometers altogether.

Mercury, a potent neurotoxin, is found in thermometers and used in a number of industrial processes. Once released into the environment, mercury makes its way into streams, rivers and, finally, the ocean. The mercury is absorbed by sea life and accumulates in the larger fish that humans like to eat, which is the main source of mercury poisoning in humans today.

While many industries follow ASTM standards that stipulate the use of mercury thermometers, these standards have fallen behind the states, many of which have outlawed the sale and transport of mercury thermometers. Presently about 300 of the approximately 700 standards have been amended to allow for the use of both mercury-free liquid-in-glass and digital thermometers.

According to NIST researcher Dawn Cross, each of these ASTM standards is reviewed on a rolling basis. She estimates that within three years all the standards will have been amended to include detailed procedures for making the switch to mercury thermometer alternatives.

“One of our major activities is fielding calls from industry and explaining the science of how they can make the switchover,” says Cross. “Change always brings confusion and apprehension, but in every case there is an alternative thermometer to suit the measurement need. It’s like learning to use a new cell phone or drive a car with a different kind of transmission. We’re simply substituting one technology for another, but they both work equally well.”

NIST itself had a stockpile of more than 8,000 industrial-use mercury thermometers hidden away in drawers. The mercury from these has been sent to specialized recycling centers, which repurpose the mercury to produce compact fluorescent light bulbs. Mercury thermometers contain about 500 mg of mercury - an amount equal to the mercury in more than 125 compact fluorescent bulbs.

The recycling doubly reduces mercury emissions, according to Greg Strouse, leader of NIST’s Temperature and Humidity Group. “The amount of mercury in a compact fluorescent light bulb is about one to four milligrams,” he says. “Most of that mercury is bound to the inside of the glass during the life-cycle of the bulb, a process that makes it much less environmentally harmful.

"Burning of coal is a major source of vaporous mercury released into the atmosphere. Compact fluorescents use less electricity, which reduces the amount of coal burned, which reduces the amount of mercury released by a factor of four.”

To learn about alternatives to industrial-use mercury thermometers and how to recycle them, go to www.epa.gov/hg/thermometer.htm.

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