The traditional mercury-in-glass thermometer, introduced in the 18th century by Daniel Gabriel Fahrenheit, was a standard tool for measuring temperature for nearly three centuries. Its reliability stemmed from mercury’s consistent thermal expansion. However, this liquid-in-glass design contained a hazardous substance. Recognizing the significant risks associated with elemental mercury, health and environmental agencies began a global movement toward safer alternatives. This transition involved regulatory actions across different countries, leading to the near-total phase-out of the mercury thermometer for general consumer use.
Why Mercury Thermometers Became a Safety Concern
The primary danger of the mercury thermometer is the elemental mercury (Hg) it contains, which is released as a toxic vapor if the glass casing breaks. Even the small amount in a typical fever thermometer can contaminate the air in a room, creating an inhalation hazard. When vaporized mercury is inhaled, it is readily absorbed by the body and can cross the blood-brain barrier.
Mercury exposure is a known neurotoxin that causes severe neurological damage and developmental problems, particularly in young children and developing fetuses. Symptoms of poisoning include tremors, memory impairment, and neuromuscular changes. Improper disposal of mercury thermometers in household trash allows them to break in landfills and release their contents into the environment.
Once released, elemental mercury settles in waterways, where microorganisms convert it into methylmercury. This highly toxic form bioaccumulates up the food chain, resulting in contaminated fish. This contamination poses a serious dietary risk, especially for pregnant women.
The Global Timeline for Phasing Them Out
The phase-out timeline began with state-level actions in the United States. States like Connecticut and Maine were among the first to ban the sale of mercury fever thermometers to the general public in 2003 and 2006, respectively. Many other states followed, creating restrictions before federal action was finalized.
Federally, the U.S. Food and Drug Administration (FDA) restricted the sale of mercury fever thermometers. The FDA clarified that these devices required premarket approval, which effectively ended the widespread sale of new clinical mercury thermometers for general consumer use in the U.S. market.
Internationally, the European Union implemented Directive 2007/51/EC, banning the sale of all new mercury fever thermometers to the public, effective April 3, 2009. The most significant global action was the Minamata Convention on Mercury, an international treaty adopted in 2013 and entering force in 2017.
The Minamata Convention designated a global phase-out date of 2020 for the manufacture, import, and export of mercury-added products, including thermometers. This agreement provided a unified deadline for nations worldwide to transition to mercury-free alternatives.
Current Alternatives to Mercury Thermometers
The market has transitioned to several safe and accurate alternatives that do not use elemental mercury. Digital thermometers are the most common replacement, relying on a temperature-sensitive resistor called a thermistor to measure heat. These battery-operated devices are fast, often providing a reading in under a minute, and display the result clearly.
Infrared thermometers measure the heat energy emitted from the body, typically used in the ear (tympanic) or across the forehead (temporal). These devices offer the fastest readings, often in just one second, and are convenient for measuring infants or uncooperative patients.
For those who prefer the traditional liquid-in-glass design, mercury-free versions are available. Some utilize alcohol dyed for visibility, while others use Galinstan, a non-toxic metal alloy. Galinstan is a mixture of gallium, indium, and tin that remains liquid at room temperature and offers accuracy comparable to mercury.
What to Do with Old Mercury Thermometers
Any mercury thermometers still in use must be handled with care and never thrown into the regular household trash or recycling bin. Improper disposal leads directly to the release of mercury vapor. If you have an old mercury thermometer, it should be treated as household hazardous waste.
To prepare the thermometer for disposal, place it in a sealed, rigid container, such as a plastic jar with a tight-fitting lid, to prevent breakage during transport. The container should then be dropped off at a local household hazardous waste collection facility or a designated mercury take-back program. These specialized facilities ensure the mercury is properly recycled or safely contained.
If a thermometer breaks, the area must be immediately ventilated, and all people and pets should leave the room. Do not use a vacuum cleaner or broom, as this will aerosolize the mercury droplets and spread the toxic vapor. Instead, carefully collect small droplets using stiff paper or a specialized cleanup kit. The collected material must then be placed into an airtight container for hazardous waste disposal.