Exposure to mercury can occur from breathing contaminated air, from eating foods that have acquired mercury residues during processing, from exposure to mercury vapor in mercury amalgam dental restorations, and from improper use or disposal of mercury and mercury-containing objects, for example, after spills of elemental mercury or improper disposal of fluorescent lamps.All of these, except elemental liquid mercury, produce toxicity or death with less than a gram. Mercurys zero oxidation state (Hg0) exists as vapor or as liquid metal, its mercurous state (Hg+) exists as inorganic salts, and its mercuric state (Hg2+) may form either inorganic salts or organomercury compounds.Consumption of whale and dolphin meat, as is the practice in Japan, is a source of high levels of mercury poisoning. Tetsuya Endo, a professor at the Health Sciences University of Hokkaido, has tested whale meat purchased in the whaling town of Taiji and found mercury levels more than 20 times the acceptable Japanese standard.Human-generated sources, such as coal-burning power plants emit about half of atmospheric mercury, with natural sources such as volcanoes responsible for the remainder. A 2021 publication investigating the mercury distribution in European soils found that high mercury concentrations are found close to abandoned mines Almadén (Castilla-La Mancha, Spain), Mt. Amiata (Italy), Idrija (Slovenia) and Rudnany (Slovakia)] and coal-fired power plants. An estimated two-thirds of human-generated mercury comes from stationary combustion, mostly of coal.
The toxic damage appears to be determined by the peak value of mercury, not the length of the exposure.Methylmercury exposure during rodent gestation, a developmental period that approximately models human neural development during the first two trimesters of gestation, has long-lasting behavioral consequences that appear in adulthood and, in some cases, may not appear until aging. Prefrontal cortex or dopamine neurotransmission could be especially sensitive to even subtle gestational methylmercury exposure and suggests that public health assessments of methylmercury based on intellectual performance may underestimate the impact of methylmercury in public health. Ethylmercury is a breakdown product of the antibacteriological agent ethylmercurithiosalicylate, which has been used as a topical antiseptic and a vaccine preservative (further discussed under Thiomersal below). Its characteristics have not been studied as extensively as those of methylmercury. It is cleared from the blood much more rapidly, with a half-life of seven to ten days, and it is metabolized much more quickly than methylmercury. It is presumed not to have methylmercurys ability to cross the blood–brain barrier via a transporter, but instead relies on simple diffusion to enter the brain. Other exposure sources of organic mercury include phenylmercuric acetate and phenylmercuric nitrate. These compounds were used in indoor latex paints for their antimildew properties, but were removed in 1990 because of cases of toxicity. Inorganic mercury compounds
Mercury occurs as salts such as mercuric chloride (HgCl2) and mercurous chloride (Hg2Cl2), the latter also known as calomel. Because they are more soluble in water, mercuric salts are usually more acutely toxic than mercurous salts.