Mercury is a chemical element that is used in mining, thermometers and dental amalgams. Exposure to mercury can be harmful to the brain and nervous system because it can cause "irritability, shyness, tremors, changes in vision or hearing, and memory problems ".1 One of the main causes of mercury poisoning is from methylmercury in fish, which cannot leave the body because it is imbedded in tissue. The main solution to get rid of worldwide mercury emissions and mercury poisoning is to limit the use of mercury, for example, in dental practice and gold mining. However, thiomersal, a mercury compound, is used in vaccines. It is not harmful and is a necessity for many people. Mercury has many harmful effects on human population so use should be limited, however, the use of thiomersal in vaccines is necessary for children in developing countries.
Mercury poisoning is a problem because water and fish get contaminated with mercury and are then consumed by humans, so if mercury use were limited, there would be less people poisoned by the fish. As the Agency for Toxic Substances and Disease Registry stated, " [mercury] enters the water or soil from natural deposits, disposal of wastes, and volcanic activity ".2 After mercury enters water, bacteria in water and the mercury produce methylmercury, which goes into the tissues of fish3. Because it is imbedded in the fish tissue, it cannot be removed when cooked, so it will be transported to the person that eats the fish. This happened in Japan in the 1960's. A factory in Minamata Bay released inorganic mercury into the bay, which caused it to go into the fish41. David A. Olson, MD, wrote, "Local villagers ate the fish and began to exhibit signs of neurologic damage, such as visual loss, extremity numbness, hearing loss, and ataxia ".5 The mercury also affected many developing fetuses, and they continued to be exposed after their birth because mercury was found in the mother's breast milk.