prevent and reverse oxidative damage, which, if the depletion is severe and long lasting, results in brain cell dysfunctions that can ultimately cause death. mercury in its various forms is particularly harmful to fetuses as an environmental toxin in pregnancy, as well as to infants. women who have been exposed to mercury in substantial excess of dietary selenium intakes during pregnancy are at risk of giving birth to children with serious birth defects, such as those seen in minamata disease. mercury exposures in excess of dietary selenium intakes in young children can have severe neurological consequences, preventing nerve sheaths from forming properly. exposure to methylmercury causes increased levels of antibodies sent to myelin basic protein (mbp), which is involved in the myelination of neurons, and glial fibrillary acidic protein (gfap), which is essential to many functions in the central nervous system (cns). this causes an autoimmmune response against mbp and gfap and results in the degradation of neural myelin and general decline in function of the cns. diagnosis diagnosis of elemental or inorganic mercury poisoning involves determining the history of exposure, physical findings, and an elevated body burden of mercury. although whole-blood mercury concentrations are typically less than 6 μg/l, diets rich in fish can result in blood mercury concentrations higher than 200 μg/l; it is not that useful to measure these levels for suspected cases of elemental or inorganic poisoning because of mercury's short half-life in the blood. if the exposure is chronic, urine levels can be obtained; 24-hour collections are more reliable than spot collections. it is difficult or impossible to interpret urine samples of people undergoing chelation therapy, as the therapy itself increases mercury levels in the samples. diagnosis of organic mercury poisoning differs in that whole-blood or hair analysis is more reliable than urinary mercury levels. prevention part of a series 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nonpoint source see misc section nutrient ocean acidification oil spill pharmaceuticals freshwater salinization septic tanks sewage septic tanks pit latrine shipping stagnation sulfur water surface runoff turbidity urban runoff water quality misc point source area source legacy pollution lists diseases law by country most polluted cities least polluted cities by pm2.5 treaties categories by country environment portal ecology portal mercury poisoning can be prevented or minimized by eliminating or reducing exposure to mercury and mercury compounds. to that end, many governments and private groups have made efforts to heavily regulate the use of mercury, or to issue advisories about the use of mercury. most countries have signed the minamata convention on mercury. the export from the european union of mercury and some mercury compounds has been prohibited since 15 march 2010. the european union has banned most uses of mercury. mercury is allowed for fluorescent light bulbs because of pressure from countries such as germany, the netherlands and hungary, which are connected to the main producers of fluorescent light bulbs: general electric, philips and osram. us environmental limits country regulating agency regulated activity medium type of mercury compound type of limit limit us occupational safety and health administration occupational exposure air elemental mercury ceiling (not to exceed) 0.1 mg/m3 us occupational safety and health administration occupational exposure air organic mercury ceiling (not to exceed) 0.05 mg/m3 us food and drug administration eating sea food methylmercury maximum allowable concentration 1 ppm (1 mg/l) us environmental protection agency drinking water inorganic mercury maximum contaminant level 2 ppb (0.002 mg/l) the united states environmental protection agency (epa) issued recommendations in 2004 regarding exposure to mercury in fish and shellfish. the epa also developed the "fish kids" awareness campaign for children and young adults on account of the greater impact of mercury exposure to that population. cleaning spilled mercury epa workers clean up residential mercury spill in 2004 mercury thermometers and mercury light bulbs are not as common as they used to be, and the amount of mercury they contain is unlikely to be a health concern if handled carefully. however, broken items still require careful cleanup, as mercury can be hard to collect and it is easy to accidentally create a much larger exposure problem. if available, powdered sulfur may be applied to the spill, in order to create a solid compound that is more easily removed from surfaces than liquid mercury. treatment identifying and removing the source of the mercury is crucial. decontamination requires removal of clothes, washing skin with soap and water, and flushing the eyes with saline solution as needed. before the advent of organic chelating agents, salts of iodide were given orally, such as heavily popularized by louis melsens and many nineteenth and early twentieth century doctors. chelation therapy chelation therapy for acute inorganic mercury poisoning, a formerly common method, was done with dmsa, 2,3-dimercapto-1-propanesulfonic acid (dmps), d-penicillamine (dpcn), or dimercaprol (bal). only dmsa is fda-approved for use in children for treating mercury poisoning. however, several studies found no clear clinical benefit from dmsa treatment for poisoning due to mercury vapor. no chelator for methylmercury or ethylmercury is approved by the fda; dmsa is the most frequently used for severe methylmercury poisoning, as it is given orally, has fewer side-effects, and has been found to be superior to bal, dpcn, and dmps. α-lipoic acid (ala) has been shown to be protective against acute mercury poisoning in several mammalian species when it is given soon after exposure; correct dosage is required, as inappropriate dosages increase toxicity. although it has been hypothesized that frequent low dosages of ala may have potential as a mercury chelator, studies in rats have been contradictory. glutathione and n-acetylcysteine (nac) are recommended by some physicians, but have been shown to increase mercury concentrations in the kidneys and the brain. chelation therapy can be hazardous if administered incorrectly. in august 2005, an incorrect form of edta (edetate disodium) used for chelation therapy resulted in hypocalcemia, causing cardiac arrest that killed a five-year-old autistic boy. other experimental animal and epidemiological study findings have confirmed the interaction between selenium and methylmercury. instead of causing a decline in neurodevelopmental outcomes, epidemiological studies have found that improved nutrient (i.e., omega-3 fatty acids, selenium, iodine, vitamin d) intakes as a result of ocean fish consumption during pregnancy improves maternal and fetal outcomes. for example, increased ocean fish consumption during pregnancy was associated with 4-6 point increases in child iqs. prognosis some of the toxic effects of mercury are partially or wholly reversible provided specific therapy is able to restore selenium availability to normal before tissue damage from oxidation becomes too extensive. autopsy findings point to a half-life of inorganic mercury in human brains of 27.4 years. heavy or prolonged exposure can do irreversible damage, in particular in fetuses, infants, and young children. young's syndrome is believed to be a long-term consequence of early childhood mercury poisoning. mercuric chloride may cause cancer as it has caused increases in several types of tumors in rats and mice, while methyl mercury has caused kidney tumors in male rats. the epa has classified mercuric chloride and methyl mercury as possible human carcinogens (atsdr, epa) detection in biological fluids mercury may be measured in blood or urine to confirm a diagnosis of poisoning in hospitalized people or to assist in the forensic investigation in a case of fatal over dosage. some analytical techniques are capable of distinguishing organic from inorganic forms of the metal. the concentrations in both fluids tend to reach high levels early after exposure to inorganic forms, while lower but very persistent levels are observed following exposure to elemental or organic mercury. chelation therapy can cause a transient elevation of urine mercury levels. history neolithic artists using cinnabar show signs of mercury poisoning. several chinese emperors and other chinese nobles are known or suspected to have died or been sickened by mercury poisoning after alchemists administered them "elixirs" to promote health, longevity, or immortality that contained either elemental mercury or (more commonly) cinnabar. among the most prominent examples: the first emperor of unified china, qin shi huang, it is reported, died in 210 bc of ingesting mercury pills that were intended to give him eternal life. emperor xuānzong of tang, one of the emperors of the late tang dynasty of china, was prescribed "cinnabar that had been treated and subdued by fire" to achieve immortality. concerns that the prescription was having ill effects on the emperor's health and sanity were waved off by the imperial alchemists, who cited medical texts listing a number of the emperor's conditions (including itching, formication, swelling, and muscle weakness), today recognized as signs and symptoms of mercury poisoning, as evidence that the elixir was effectively treating the emperor's latent ailments. xuānzong became irritable and paranoid, and he seems to have ultimately died in 859 from the poisoning. the phrase mad as a hatter is likely a reference to mercury poisoning among milliners (so-called "mad hatter disease"), as mercury-based compounds were once used in the manufacture of felt hats in the 18th and 19th century. (the mad hatter character of alice in wonderland was, it is presumed, inspired by an eccentric furniture dealer named theophilus carter. carter was not a victim of mad hatter disease although lewis carroll would have been familiar with the phenomenon of dementia that occurred among hatters.) in 1810, two british ships, hms triumph and hms phipps, salvaged a large load of elemental mercury from a wrecked spanish vessel near cadiz, spain. the bladders containing the mercury soon ruptured. the element spread about the ships in liquid and vapor forms. the sailors presented with neurologic compromises: tremor, paralysis, and excessive salivation as well as tooth loss, skin problems, and pulmonary complaints. in 1823 william burnet, md published a report on the effects of mercurial vapor. triumph's surgeon, henry plowman, had concluded that the ailments had arisen from inhaling the mercurialized atmosphere. his treatment was to order the lower deck gun ports to be opened, when it was safe to do so; sleeping on the orlop was forbidden; and no men slept in the lower deck if they were at all symptomatic. windsails were set to channel fresh air into the lower decks day and night. historically, gold-mercury amalgam was widely used in gilding, applied to the object and then heated to vaporize the mercury and deposit the gold, leading to numerous casualties among the workers. it is estimated that during the construction of saint isaac's cathedral alone, 60 men died from the gilding of the main dome. for years, including the early part of his presidency, abraham lincoln took a common medicine of his time called "blue mass", which contained significant amounts of mercury. on september 5, 1920, silent movie actress olive thomas ingested mercury capsules dissolved in an alcoholic solution at the hotel ritz in paris. there is still controversy over whether it was suicide, or whether she consumed the external preparation by mistake. her husband, jack pickford (the brother of mary pickford), had syphilis, and