Due to its unique properties, mercury is a useful, versatile component of many modern tools.  This substance is found often in its liquid elemental state, in devices such as barometers, manometers, thermometers, and thermostats.  Despite the numerous common uses of mercury, however, it is one of the most harmful of the heavy metals.

When these mercury-containing appliances are disposed of, they are often incinerated or dumped into landfills.  The presence of mercury in landfills pollutes the nearby ground water, and incineration introduces mercury vapors into the atmosphere.  These mercury vapors circulate for long periods of time in the atmosphere, diffusing over a wide-spread area.  From there, the vapors settle in the environment, typically in the aquatic ecosystem.  The mercury accumulates in contaminated plants and animals faster than it can be naturally reduced.  As animals farther up the food chain consume contaminated prey, the concentrations of mercury increase significantly, in a process known as mercury biomagnification.