Mercury
Mercury and most of its compounds are extremely toxic and are generally handled with care; in cases of spills involving mercury (such as from certain thermometers or fluorescent light bulbs) specific cleaning instructions should be used to avoid toxic exposure.[22] It can be inhaled and absorbed through the skin and mucous membrane, so containers of mercury are securely sealed to avoid spills and evaporation. Heating of mercury, or compounds of mercury that may decompose when heated, should always be carried out with adequate ventilation in order to avoid exposure to mercury vapor. The most toxic forms of mercury are its organic compounds, such as methylmercury.

Mercury Poisening
Mercury poisoning (also known as mercurialism or hydrargyria, or acrodynia when affecting children) is a disease caused by exposure to mercury or its toxic compounds. Mercury is a cumulative heavy metal poison which occurs in its elemental form, inorganically as salts, or organically as organomercury compounds; the three groups vary in effects due to differences in their absorption and metabolism, among other factors.[1] However, with sufficient exposure all mercury-based toxins damage the central nervous system and other organs or organ systems such as the liver or gastrointestinal tract.
Symptoms typically include sensory impairment (vision, hearing, speech), disturbed sensation and a lack of coordination. The type and degree of symptoms exhibited depend up on the individual toxin, the dose, and the method and duration of exposure.
Due to its toxicity, there have been campaigns in many countries to ban mercury altogether.