The mercury-in-glass thermometer, once a common household and clinical device, utilizes elemental mercury to measure temperature. It consists of a glass capillary tube connected to a bulb reservoir, where the silvery liquid expands and contracts, indicating the temperature on an etched scale. Although accurate, the inherent toxicity of mercury has led to a widespread phase-out. Concerns remain about older devices, as breakage can release the metallic liquid, creating an environmental and health hazard.
Identifying Mercury Thermometers
Distinguishing a mercury thermometer from modern alternatives is important for safety, as they share a similar glass-tube design with alcohol-filled models. Mercury thermometers are characterized by a shiny, silver-colored liquid in the bulb and capillary tube, distinct from alcohol thermometers, which use dyed liquids like red or blue. Digital thermometers use electronic sensors and display temperature numerically, containing no liquid metal. Due to recognized hazards, the sale of mercury thermometers has been largely restricted globally. However, older devices may still be found in homes, medical kits, or specialized laboratory and industrial environments, necessitating awareness of the risks they pose if damaged.
Quantifying the Mercury Content
The amount of elemental mercury contained within a glass thermometer varies depending on its purpose and design. A standard clinical or fever thermometer typically holds 0.5 to 0.7 grams of mercury. Basal temperature thermometers, which are engineered to measure slight temperature fluctuations, may contain up to 2.25 grams.
While the quantity may seem minimal, the dense, silvery liquid poses a significant risk if improperly handled after breakage. Larger industrial or laboratory thermometers can contain substantially more mercury, sometimes several grams. Regardless of the size, the core concern is not the liquid mass itself but the toxic vapor released when the metal is exposed to air.
Health Risks of Mercury Exposure
The primary health risk from a broken mercury thermometer is inhaling the colorless, odorless vapor that elemental mercury emits at room temperature. This neurotoxin easily vaporizes, is readily absorbed by the lungs, and circulates throughout the body. Once absorbed, it crosses the blood-brain barrier, making the central nervous system vulnerable to damage.
Acute exposure can cause immediate symptoms such as coughing, chest pain, and difficulty breathing, potentially resulting in lung damage. Prolonged exposure from an incomplete cleanup can cause chronic effects, including neurological issues like tremors, memory problems, and personality changes, as well as kidney damage. Developing fetuses and young children are especially susceptible because their nervous systems are still maturing.
Safe Cleanup and Disposal
Cleaning up a small mercury spill from a broken thermometer requires a precise protocol to minimize toxic vapor release and prevent contamination. First, ventilate the area immediately by opening windows and doors, and remove children and pets from the room. Avoid using a vacuum cleaner, as its operation heats the mercury and aerosolizes the liquid, significantly increasing vapor concentration. Similarly, using a broom or brush will only break the mercury into smaller, harder-to-collect droplets, spreading the contamination.
To collect the spilled mercury, a piece of stiff paper or cardboard can be used to gently push the beads together into a single, larger ball. Small droplets can be picked up using an eyedropper or the sticky side of duct tape. A flashlight shined at a low angle can help locate any remaining reflective beads. All cleanup materials, including the broken glass, gloves, and paper towels, must be placed into a sealable plastic bag or container. This container must then be treated as hazardous waste and taken to a local household hazardous waste collection site for proper disposal, as mercury is not permitted in regular trash or down any drain.