Mercury is a poisonous environmental pollutant whose greatest source is the emission from the lithosphere. Other major sources are industry and burning of wastes and fossil fuels. Mercury exists in three forms: elemental mercury, inorganic mercury compounds and organic mercury. Mercury eventually settles in waterways where it is converted to the toxic (organic) methylmercury by bacteria and algae. This is especially pronounced in areas where lakes are shallow and have large catchment areas. When soil and lakewaters are relatively acidic, it enhances the availability of soil mercury and can lead to drainage of high-mercury water from swamps into lakes.

People are mainly exposed to methylmercury, an organic compound, when they eat fish and shellfish that contain methylmercury. Whether an exposure to the various forms of mercury will harm a person’s health depends on a number of factors (below). The factors that determine how severe the health effects are from mercury exposure include these:

• the chemical form of mercury (methylmercury is more toxic than elemental mercury);
• the dose;
• the age of the person exposed (the fetus is the most susceptible);
• the duration of exposure;
• the route of exposure — inhalation, ingestion, dermal contact, etc.; and
• the health of the person exposed.

Remote sensing can be used in determining many aspects of the lithosphere and changing environment.