It was one of Daniel Gabriel Fahrenheit's most famous inventions, in 1714. But after nearly 300 years on the market, the still-common mercury thermometer now appears headed for extinction.
While many Maryland residents probably still have them in their medicine cabinets, or on their walls, the retail sale of mercury thermometers has been banned in Maryland since 2002 because of mercury's hazards as a powerful neurotoxin.
There are similar bans or restrictions in at least 17 other states, with more such legislation pending elsewhere, according to the Interstate Mercury Education and Reduction Clearinghouse.
Mercury thermometers are also on their way out in a wide variety of industries, along with a long list of other measuring devices, thermostats and switches that rely on mercury components.
And beginning March 1, the National Institute of Standards and Technology, in Gaithersburg, will no longer provide calibration services for manufacturers and users of mercury-in-glass thermometers — a critical service it had provided to American industry since 1901.
NIST and the Environmental Protection Agency are taking other regulatory steps that would limit the use of those mercury-based products, and provide alternatives.
"Due to elemental mercury's high toxicity, EPA seeks to reduce potential mercury exposures to humans and the environment by reducing the overall use of mercury-containing products, including mercury-containing thermometers," said EPA spokesman Dale Kemery.
Within five years, NIST officials expect the mercury thermometer will be officially obsolete. And none too soon.
Exposure to high levels of metallic mercury vapors can cause permanent damage to the brain, kidneys and a developing fetus. Brain damage can result in irritability, behavioral changes, tremors, changes in vision, hearing and memory problems, according to the Centers for Disease Control and Prevention.
Many manufacturers and other industries have moved away from mercury devices, either out of concerns about the hazards and costs of breakage and cleanups, or because they have found something better.
"They have become obsolete in various industries as we work to remove them from the measurement stream, and find alternative thermometers," said Greg Strouse, leader of NIST's Temperature and Humidity Group.
If you were to compare the technologies available today, he said, "mercury is usually the least accurate of all current thermometers in the marketplace. Digital manufacturers have worked extremely hard to create products that work to meet the needs of end users, and usually better."
"We have yet to find an application that we can't solve with an alternate thermometer," Strouse said.
For those still using mercury devices, NIST is working with the EPA and private industry to revise more than 700 federal product standards that have long required the use of mercury thermometers, and find alternatives.
They will identify practical alternative thermometers, and write them into the new standards.
Almost half of those standards have already been amended to allow the use of non-mercury liquids in glass, or digital thermometers using electronic sensors. The process is expected to take several more years.
The EPA has also proposed new rules that would introduce more such flexibility into both the federal Clean Air Act and the Toxic Substances Control Act, where they currently require the use of mercury thermometers.
Accurate temperature readings are critical to many industrial processes, and commercial applications such as storage facilities for blood or vaccines.
One of the last and biggest challenges for NIST is the petrochemical industry. Natural gas, oil and other fuels expand as they warm up, so temperature measurements are critical to gauging the amount of gas or oil in, or dispensed from, a storage tank. And the industry's measurement standards have long required finely calibrated mercury-in-glass thermometers.
NIST has begun working with the American Petroleum Institute and the American Society for Testing and Materials (an international body that develops consensus technical standards for industry) to identify thermometer technologies that can replace mercury.
"Give them credit for level of effort," Strouse said. "There's a lot of culture behind their measurements and a lot of money attached. They need to be sure the replacements work to the level they need them to."
The declining demand from business and industry for calibration of mercury thermometers at NIST labs tells the tale best.
"Back in the early 1900s, they employed five people to do nothing more than calibrate mercury thermometers," Strouse said. "When I started here 20-some years ago, there was one person in the lab calibrating close to a thousand of them a year. Last year we calibrated four."
And so far in 2011, there have been none. Nor is there any clamor from thermometer manufacturers to save the devices from oblivion.
Only one U.S. manufacturer of mercury thermometers — Miller & Weber, in Queens, N.Y. — remains in business. And it, too, is working "extremely hard" to help phase out the technology, and sell customers its more advanced products, Strouse said.
Thermometers aren't the only concern. There is mercury in a variety of measuring devices, including some barometers, strain gauges, flow meters, blood-pressure cuffs, and in some electric switches, like the ones that turn on automobile trunk lights when the lids are lifted.
In 2001, Maryland banned elemental mercury and mercury-added devices from the state's primary and secondary schools, except vocational schools. Subsequent collections removed 6,845 devices and 349 pounds of mercury.
"The law is they're not supposed to be there," said MDE spokesman Jay Apperson.
But evidently some remain. On Feb. 11, after a mercury-filled scientific thermometer broke in a Baltimore elementary school, at least 20 students and three teachers found themselves surrounded by hazardous materials teams.
No one was sickened and no one required decontamination, according to the Maryland Department of the Environment. But 20 pairs of shoes were sent to a hazardous waste landfill and the school system faced a costly cleanup.
A broken mercury barometer in a science teacher's office in 2004 caused the evacuation of a section of South Carroll High School.
But for most Americans, the nearest mercury is probably in their home thermostats. Millions still have the iconic, round "T87F" Honeywell thermostats, or others like it, on their walls.
"It is the second-most-recognized corporate symbol in the world, after the Coke bottle," said William G. O'Connor, energy efficiency district manager in Baltimore for Honeywell.
The company works with Baltimore Gas and Electric Co. to collect and recycle 800 to 1,000 old thermostats a week — 60 percent of them containing mercury switches — as they're replaced with programmable digital thermostats under BGE's Peak Rewards program.
Each mercury thermostat contains a glass bulb holding at least 2.8 grams of mercury. The mercury is part of the switch that turns the furnace, heat pump or air conditioner on and off. That's the equivalent of the mercury in five or six fever thermometers.
Since 2009, BGE has replaced almost 61,000 residential mercury thermostats and recycled 507 pounds of mercury. Customers who elect not to turn over the old device to BGE are instructed in how to dispose of it safely.
But there are millions more in schools, offices and plants, and they continue to be damaged or vandalized, with costly results.
In May 2007, 30 students and four adults at Waverly Elementary and Middle School in Baltimore had to be decontaminated after students ripped thermostats off the walls, stomped on them and released the mercury.
Mercury vapor levels in the school were tested and found to be high, and several surfaces were contaminated. Three students were taken into custody.
A growing number of states, including Maryland, have banned their sale. Three major thermostat manufacturers — Honeywell, General Electric and White-Rogers — have stopped making devices with mercury switches. They formed a nonprofit corporation, Thermostat Recycling Corp., or TRC, to collect and recycle all brands of wall-mounted mercury thermostats, including those from BGE, contractors and local hazardous waste programs.
Between 1998 and 2006, TRC collected 560,000 thermostats nationwide, containing more than 21/2 tons of mercury.
Even so, most old mercury thermostats are probably just thrown away, and their mercury goes illegally into landfills and incinerators.
A calculation by the Northeast Waste Management Officials' Association estimated that, in Massachusetts in 2006 alone, more than 107,000 mercury thermostats containing 710 pounds of mercury entered the state's waste stream.
Of those, only about 6 percent were recovered by TRC and other community programs.
For local hazardous waste recycling resources: http://bsun.md/eSvzxa
Mercury in your home
Although they are being phased out, older devices may still contain mercury, including:
Safety shutoffs in irons and washers
Trunk light in your car
Lawnmower fuel-level indicatorCopyright © 2014, The Baltimore Sun