Elemental mercury exposure

Wildlife toxicologists should be attuned to developments in human health mercury, as assays that have been used successfully on humans may be suitable or adaptable for other vertebrate species. Echeverria and co-workers (Echeverria et al. 2005, 2006 Heyer et al. 2006) have characterized a gene encoding coproporphyrinogen oxidase, a gene in the heme biosynthetic pathway. Polymorphism in this gene predicts differential response to elemental mercury exposure in human subjects. Plans to modify this assay for other mercury species in matrices from wildlife are under way. 

Albers JW, Kallenbach LR, Fine LJ, et al. 1988. Neurological abnormalities associated with remote occupational elemental mercury exposure. Ann Neurol 24(5) 651-659. 

Hudson PJ, Vogt RL, Brondum J, et al. 1987. Elemental mercury exposure among children of thermometer plant workers. Pediatrics 79 935-938. 

Levine SP, CavenderGD, LangolfGD, etal. 1982. Elemental mercury exposure Peripheral neurotoxicity. Br J Ind Med 39 136-139. 

Thorp JM Jr, Boyette D, Watson WJ, et al. 1992. Elemental mercury exposure in early pregnancy. Obstet Gynecol 79(5 Pt 2) 874-876. 

Wildlife indicators of mercury exposure and trends are important elements of a comprehensive approach to assess mercury in the environment and the monitoring of trends that may assist regulators and the regulated community in long-term evalnation of the need and usefulness of mercury somce controls. It is important to understand, however, that bioindicator data alone are insufficient to answer snch critical qnestions as identification of mercniy sonrces, or the relative importance of local, regional, and global inputs of mercury somces to atmospheric deposition and errvirorrmerrtal loading in specific areas. 

Steffek AJ, Clayton R, Slew C et al Effects of elemental mercury vapor exposure on pregnant Sprague-Dawley rats. Teratology 35(2) 59 (abst), 1987... 

The elemental mercury is converted to methyl mercury by bacteria after which it moves up the food chain, often in fish that are consumed by a range of animals and humans. Local miners, their families, and particularly children suffer from mercury exposure. 

Elemental mercury in the form of mercury vapor is readily and rapidly absorbed into the bloodstream when inhaled and easily crosses the blood-brain barrier and the placenta. Oral ingestion of elemental mercury is far less hazardous than inhalation of mercury vapor due to its poor absorption in the gut. Acute, high level exposure to mercury vapor can result in respiratory, cardiovascular, neurological, and gastrointestinal effects, and even death. 

C. The symptoms are characteristic of a person chronically exposed to vapors released from elemental mercury. Since the dental technician may handle elemental mercury, including mishandling, the symptoms presented may occur. While the technician may be exposed to solvent vapors released from dental adhesives, the symptoms are not characteristic of this type of exposure. Fluoride toxicity would not be expected because these are not symptoms associated with fluoride ingestion, and the patient and not the technician would be most likely exposed to quantities high enough to cause any symptoms. The technician has little exposure to li-docaine, and the symptoms are not typical of lido-caine toxicity. 

Unithiol and succimer increase urine mercury excretion following acute or chronic elemental mercury inhalation, but the impact of such treatment on clinical outcome is unknown. Dimercaprol has been shown to redistribute mercury to the central nervous system from other tissue sites, and since the brain is a key target organ, dimercaprol should not be used in treatment of exposure to elemental or organic mercury. Limited data suggest that succimer, unithiol, and N- acetyl-L-cysteine (NAC) may enhance body clearance of methylmercury. 

Elemental Mercury Vapor. Although there may be toxic effects to the respiratory system from the inhalation of mercury vapor, the major toxic effect is to the CNS. This is especially true after chronic exposure. There are a variety of symptoms such as muscle tremors, personality changes, delirium, hallucination, and gingivitis. 

Mercury exists in three forms elemental, inorganic, and organic with different toxic effects. Elemental mercury is absorbed as a vapor and may enter the CNS and cause toxicity there. Inorganic mercury is poorly absorbed, but the cysteine conjugate of mercury is concentrated in the kidney by active transport. The kidney is the main target organ (also gastrointestinal tract if exposure by that route). 

Mercury exists in the environment in three main chemical forms elemental mercury (Hg°), inorganic mercurous (Hg+) and mercuric (Hg2+) salts, and organic methylmer-cury (CH3Hg) and dimethylmercury (CH3HgCH3) compounds. Elemental mercury, in the form of mercury vapor, is almost completely absorbed by the respiratory system, whereas ingested elemental mercury is not readily absorbed and is relatively harmless. Once absorbed, elemental mercury can cross the blood-brain barrier into the nervous system. Most exposure to elemental mercury tends to be from occupational sources. 

Global changes and extensive industrialization during the twentieth century made animals and humans become exposed to a variety of chemicals. Exposure to chemical forms of mercury (e.g., elemental mercury vapor [Hg°], inorganic mercury [Hg+] and mercuric [Hg2+], organic mercury [R-Hg+ or R—Hg—R])... 

Although mercury has been used in spring tonics, as a cure for syphilis, and a panacea for other afflictions, it is now recognized as a highly toxic trace metal that concentrates in aquatic food webs. According to Clarkson (1997), the principal human exposure to inorganic mercury species is from elemental mercury vapor, which is derived principally from industries such as gold and silver... 

Boogaard PJ, Houtsma AT, Journee HL, Van Sittert NJ. Effects of exposure to elemental mercury on the nervous system and the kidneys of workers producing natural gas. Arch Environ Health 1996 51(2) 108-15. 

Smith PJ, Eangolf GD, Goldberg J. Effects of occupational exposure to elemental mercury on short term memory. Brit J Ind Med 1983 40 413-9. 

Bluhm RE, Bobbit RG, Welch LW, Wood AJ. Elemental mercury vapour toxicity, treatment and prognosis after acute, intensive exposure in chloralkali plant workers. Part I History, neuropsychological findings and chelator effects. Human ExpToxicol 1992 11 201-10. 

Absorption varies significantly according to the form of exposure (elemental, inorganic, or organic). Inhaled mercury vapor crosses through the alveolar cells readily, is 75% absorbed, and is carried by the red blood cells. Catalase in these cells oxidizes elemental mercury almost at once to the divalent state. Alcohol inhibits the catalase activity however, in the seconds it takes for a complete blood circulation cycle, a significant amount of free mercury can cross the blood-brain barrier. 

The general population is most commonly exposed to mercury primarily from two sources (1) eating fish and marine mammals (e.g., whales, seals) that may contain some methylmercury in their tissues or (2) from the release of elemental mercury from the dental amalgam used in fillings. It is not known how much of the elemental mercury released from dental amalgam is inhaled as a mercury vapor, how much is breathed out, how much is swallowed in a liquid form, or how much is converted into a mercuric salt that is either swallowed of directly absorbed into the oral mucosa. Exposure to mercury, however, does not... 

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