Classic glass thermometers, once common household items, contain a small amount of elemental mercury, typically about 0.5 to 0.6 grams. When intact, the mercury is safely sealed within the glass tube, posing virtually no danger. The primary risk arises only if the glass breaks, allowing the liquid metal to escape and vaporize into the surrounding air. This potential for exposure to mercury vapor is why these thermometers have largely been phased out of medical and home use.
Understanding Elemental Mercury and Its Danger
The mercury found in thermometers is elemental or metallic mercury, a dense, silvery-white liquid. At room temperature, this form of mercury slowly releases an odorless, invisible vapor into the air. The greatest danger is through the inhalation of these vapors, which are readily absorbed through the lungs and carried quickly into the bloodstream.
Once absorbed, the vapor can cross the blood-brain barrier, where it accumulates and causes neurological damage. Acute inhalation of high concentrations may lead to severe symptoms such as cough, breathlessness, and chest tightness. Chronic exposure can result in neurological issues like fine tremors, sensory impairment, and personality changes.
Elemental mercury differs from methylmercury, the organic form associated with contaminated fish. Methylmercury is highly toxic when ingested because it is almost completely absorbed by the digestive tract. Elemental mercury is poorly absorbed if swallowed, posing a low risk if accidentally ingested. However, it remains a significant inhalation hazard if the spill is not cleaned completely.
Protocol for Cleaning Up a Broken Mercury Thermometer
If a mercury thermometer breaks, immediately evacuate all people and pets from the room to prevent vapor inhalation. Open a window to ventilate the area to the outside. Keep the room temperature below 72°F, as cooler temperatures reduce vaporization. Turn off central heating or air conditioning, and close interior doors to prevent the vapor from spreading.
Before cleanup, put on gloves made of nitrile, latex, or rubber. Never use a vacuum cleaner, as the heat and air movement will aerosolize the mercury, significantly increasing the toxic vapor concentration. Do not use a broom, as it will break the mercury beads into smaller, harder-to-collect droplets.
The goal is to gather the distinct, shiny beads into a single mass. Use two stiff pieces of paper or cardboard to gently push the droplets together. A flashlight shined at a glancing angle helps locate small, scattered beads. Use an eyedropper to suction up the beads, or gently press a piece of duct tape onto the affected area to pick up smaller particles.
All collected mercury, broken glass, and cleanup materials must be placed into a single, sealable, non-metallic container, such as a zip-top plastic bag or a glass jar with a tight lid. Never pour the mercury down a drain, as it can accumulate in the plumbing and continue to emit vapor. Contact your local health department or municipal waste authority for specific instructions on hazardous waste disposal.
Safer Alternatives and Current Usage Regulations
Due to the toxicity of elemental mercury and the difficulty of spill cleanup, mercury-in-glass thermometers have been largely eliminated in homes and medical facilities. Many states and countries have enacted regulations to ban or phase out the sale of these devices, providing an incentive for manufacturers and consumers to switch to safer alternatives.
The most common replacement is the digital thermometer, which uses electronic sensors to quickly and accurately measure temperature. These devices are durable, easy to read, and present no risk of a mercury spill.
Another alternative is the liquid-in-glass thermometer that uses a non-toxic liquid instead of mercury. One specific non-mercury liquid is the alloy Galinstan, a mixture of gallium, indium, and tin. Galinstan is not toxic when swallowed or inhaled, and thermometers containing this substance are often labeled as “mercury-free.” The availability of these safe and effective alternatives means that mercury thermometers are now considered obsolete for routine temperature measurement.