Chronic mercury toxicity results from:
Inhalation while removing old amalgam
Skin contact
Mercury vapour
All of the above
All the options given in the question lead to mercury toxicity.
Methyl mercury is the most common form that is transformed by natural processes; it is a more toxic form than ethyl mercury (C2H5Hg+) or elemental mercury. Methyl mercury is a major safety concern because it bioaccumulates through the food chain; its pharmacokinetic half-life is longer (1.5 to 3 months) than that of ethyl mercury (less than 1 week). In air, the concentrations of mercury range from about 0.01 to 0.02 µg/m3.
Mercury accumulates in the kidneys. In the brain, metallic mercury can be converted to an inorganic form that is retained in the brain. Elemental mercury and mercury vapor have a half-life of 1 to 3 months. Mercury leaves the body by excretion through urine and feces.
Exposure to high levels of mercury can injure the brain, kidneys, and developing fetus. Chronic mercury toxicity may be manifested as tremors; memory loss; and changes in personality, vision, and hearing.
Reference: PHILLIPS’ SCIENCE OF DENTAL MATERIALS, 12th ed page no 124