Older conventional thermostats commonly contain which hazardous material requiring special disposal?

• A. Lead
• B. Asbestos
• C. Mercury
• D. Cadmium

Answer: (C)

Older conventional thermostats used a mercury switch to sense temperature. Mercury is a toxic heavy metal, and if a device breaks or is mishandled, mercury can be released as vapor and contaminate air or water. Because of this risk, thermostats containing mercury are treated as hazardous waste and must be disposed of through proper channels—such as household hazardous waste programs or certified recyclers that can safely recover the mercury. Modern thermostats no longer use mercury, often relying on electronic or non-mercury switching methods.