NIST researcher Dawn Cross calibrates a mercury thermometer using the icepoint of water as a reference. NIST will cease to offer this service on March 1, 2011, in order to support efforts to reduce the amount of mercury in the environment. Credit: NIST
March 1, 2011, the National Institute of Standards and Technology
(NIST) will no longer provide calibration services for mercury
thermometers. The cessation of the mercury thermometer calibration
program marks the end of an era at NIST, which has provided the service
since the doors opened in 1901. The closing of the program is part of a
larger effort, in collaboration with the U.S. Environmental Protection
Agency (EPA) and a number of professional standards organizations and
environmental and industry groups, to phase out the use of mercury
is a potent neurotoxin. Elemental mercury is found in thermometers and
used in a number of industrial processes such as gold mining. 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. This is the main
source of mercury poisoning in humans today.
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
to NIST researcher Dawn Cross, each of these ASTM standards is reviewed
on a rolling basis. She estimates that all the standards will have been
amended to include detailed procedures for making the switch to mercury
thermometer alternatives within three years.
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.
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 milligrams of mercury—an amount
equal to the mercury in over 125 compact fluorescent bulbs.
According to Greg Strouse, leader of NIST’s Temperature and Humidity Group, that recycling doubly reduces mercury emissions.
amount of mercury in a compact fluorescent light bulb is about one to
four milligrams,” says Strouse. “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