What is mercury?
Mercury is a bioaccumulative, persistent, and toxic heavy metal that threatens human and ecosystem health.

Mercury is present in the natural environment in small quantities, however, since the industrial age, humans have elevated the levels of mercury in the environment to several times their natural levels. Mercury is released when coal is burned to produce electricity, through the manufacture, breakage, or disposal of mercury-containing products (such as mercury switches, thermometers, thermostats, and compact fluorescent light bulbs), and through industrial processes such as mining and chemical manufacturing.

Mercury is a potent and dangerous neurotoxin which is dangerous to the health of people and wildlife. Older mechanical thermostats can have 1-4 mercury switches, each containing approximately 2.5 grams of mercury. Just one gram of mercury can contaminate an eight-hectare lake to the point where the fish in that lake are not edible for one full year.

This older thermostat contains four mercury switches. See the silvery liquid in the bulbs? Each of these switches contains about 2.5 grams of mercury.